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Detection of Banned and Restricted Ozone-DepletingChemicals in Printed Circuit BoardsRichard N. Lee a & Bob W. Wright aa Chemical and Biological Sciences, National Security Directorate, Pacific Northwest NationalLaboratory , Richland, WA, USAPublished online: 11 Dec 2008.

To cite this article: Richard N. Lee & Bob W. Wright (2008) Detection of Banned and Restricted Ozone-Depleting Chemicals inPrinted Circuit Boards, Environmental Forensics, 9:4, 320-339

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Environmental Forensics, 9:320–339, 2008Copyright C© Taylor & Francis Group, LLCISSN: 1527–5922 print / 1527–5930 onlineDOI: 10.1080/15275920802502083

Detection of Banned and Restricted Ozone-Depleting Chemicalsin Printed Circuit Boards

Richard N. Lee and Bob W. Wright

Chemical and Biological Sciences, National Security Directorate, Pacific Northwest National Laboratory, Richland, WA, USA

A more-than-5-year study directed toward the detection of trace residual halogenated solvents in circuit boards was recently completed.This work was undertaken to demonstrate the potential for reliable detection of solvents used during the fabrication of printed circuitboards found in a wide variety of electronic products. Residual solvent detection was demonstrated for spiked boards after an agingperiod of 5 months and for printed circuit boards removed from a variety of used (at least 5 years old) and new electronic products.The analytical system and standard operating procedure developed during this study provide the tools required to assess and confirmcompliance with regulations associated with the use of ozone depleting chemicals.

Keywords: ozone-depleting chemicals, Montreal Protocol, residual solvents, purge and trap, precision cleaning, thermal desorptionanalysis

The objective of this work was to develop and validate a purgeand trap (P&T) technique to detect residual solvents used in thefabrication of printed circuit boards (PCBs), or their compo-nents, and to provide a tool for measuring regulated and bannedindustrial chemicals related to stratospheric ozone depletion andglobal warming. P&T is a widely applied technique (Bianchiet al., 1991) for the concentration of volatile and semi-volatileanalytes in environmental samples before separation and analy-sis by gas chromatography (GC). Highly sensitive analyte detec-tion (Simmonds et al., 1974, Shapiro et al., 2004) was achievedfor the halogenated solvents of interest by employing an electroncapture detector (ECD).

Previous studies directed at the detection of residual sol-vents are dominated by work focusing on environmental ma-trices, primarily soils, sediments and solid wastes. Where in-terest has extended to commercial products, it was initiated inresponse to concerns related to surface ozone concentrationsand the inhalation or ingestion of solvents, and the consequentimpact on human health. Sampling methods applied to the de-tection of emissions from commercial products have benefitedfrom the wealth of information developed for characterizationof ambient and workplace atmospheres. This information isdocumented in methods developed under United States Envi-ronmental Protection Agency (USEPA) direction in responseto its mandate to understand, characterize and provide guid-ance for responding to environmental issues (USEPA, 2002 and

Received 11 July 2007; accepted 6 March 2008.Address correspondence to Bob W. Wright, Chemical and Biolog-

ical Sciences, National Security Directorate, Pacific Northwest Na-tional Laboratory, P. O. Box 999, Richland, WA 99352, USA. E-mail:[email protected]

USEPA, 1999a, 1999b). Products examined for residual sol-vents include building materials (American Society for Test-ing and Materials [ASTM], 2005, 2006; California Departmentof Health Services [DHS], 2004), pharmaceuticals (Schuberth,1996; Wittrig et al., 2004; International Conference on Harmo-nization [ICH], 1996, 1997), foods (Fleming-Jones et al., 2003;Heikes et al., 1995), as well as personal care products (CaliforniaEPA, 2003, 2005a, 2005b; Rickman et al., 1997a, 1997b) andelectronic products (Bjorn-Hansen, 2003; European ComputerManufacturers Association [ECMA], 2001). Analytical meth-ods utilized during these studies employed several different va-por concentration techniques, including P&T (Schumacher andWard, 1997), headspace (George et al., 1997) and solid phasemicroextraction (Urakami et al., 2004) followed by GC anal-ysis. While many of the volatile organic compounds (VOCs)associated with these investigations are also ozone-depletingcompounds (ODCs), the study reported here represents a sig-nificant departure from a focus on local, health-related impactsto addressing the ultra-sensitive detection of restricted chem-icals in industrial parts manufacturing. Studies that have fo-cused on electronic products were generally not restricted tosingle components, such as PCBs, and were concerned withhealth related impacts from inhalation. Only widely used indus-trial solvents were reported (chloroform, trichloroethene [TCE]and tetrachloroethene [PCE]) and a single reference to PCBsreports the detection of only aldehydes and ketones associatedwith phenol/paper-based and glass/epoxy-based PCBs (USEPA,1998).

Rigid substrates employed for the production of PCBs usedin many consumer products are resin-impregnated paper (FR-2)or glass fiber (FR-4). These matrices are sufficiently porous andadsorptive to trap cleaning solvents used during PCB fabrica-tion. Since a circuit board and its components may be exposed

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Ozone-Depleting Chemicals 321

to a variety of solvents during assembly and associated oper-ations, these solvents could be retained by the circuit board’sfiber reinforced polymer matrix and released over time (Manko,1995). The detection of these residual solvents is dependenton the rate of their release and the sensitivity of the detectionmethod. Given the detection sensitivity of the ECD to halo-genated compounds, the question was reduced to whether thesesolvents were retained within the circuit board matrix for suf-ficient time and released at a rate that permitted unequivocalidentification over an aging period spanning months to years.Such residues should be released, concentrated and detected byapplication of a P&T sample collection procedure preceding GCanalysis. This technique can be used to ensure compliance withrelevant laws and regulations restricting use of industrial sol-vents associated with adverse environmental impact. Althoughthis study focused on small PCBs (up to approximately 6 ×10 inches), the technique described could be applied to largerboards.

A discussion of solvents identified as ODCs is presented inthe Appendix. Precision cleaning operations represent a sig-nificant application area for these chemicals. Of particular in-terest were 1,1,2-trifluoro-1,2,2-trichloroethane (CFC-113) andmethyl chloroform (TCA) (solvents historically linked to cir-cuit board production), and common industrial halocarbons thatmight be available as substitutes for these solvents. In the mod-ified P&T procedure reported here, a circuit board sample isenclosed in a container and purged with high-purity helium toremove ambient air. Subsequent purge of the container with highpurity helium was accompanied by cryogenic collection of aconcentrated purge gas sample for GC/ECD analysis. A bread-board system was used to investigate analyte detection usingsolvent spiked circuit boards and aged boards removed from re-tired laboratory and office equipment. This system also providedoperational experience essential to the design of a dedicated GCsystem specifically devoted to residual solvent detection thatwas developed during this study for use in assessing compliancewith restrictions placed on ODC solvents. Both analytical sys-tems are described in the following sections along with variousstudies used to assess system performance and data interpre-tation. Finally, the results of these studies led to developmentof a dedicated P&T system and a standard operating proce-dure (SOP) (Pacific Northwest National Laboratory [PNNL],2007) for trace detection of residual solvents associated withPCBs.

Experimental Design

Solvents

Method development work emphasized halocarbons that havebeen or could be used in the electronics industry for PCBproduction. The chromatographic retention properties of thesechemicals were characterized as a prerequisite to their iden-tification during the examination of PCBs taken from com-mercial products or purchased off the shelf. Prominent halo-

carbon solvents, freon replacements, and the ODC chemicalscarbon tetrachloride, 1,1,1-trichloroethane (TCA), and CFC-113 for chromatographic standard preparation were purchasedfrom Sigma-Aldrich Chemical (St. Louis, MO) or Chem Service(West Chester, PA). Other ODCs, not available in the US, werepurchased from ABCR Specialty Chemicals (Karlsruhe, Ger-many). In addition to their use in standards, some halocarbonswere used to prepare spiked PCBs for investigating solvent re-tention by circuit board matrices. This required preliminary anal-ysis of a PCB “blank,” exposure to one or more known solventsand a sufficiently long pre-analysis aging time to demonstratethat solvent loss rates were low enough to provide evidence thatresidual solvent detection in products received at retail outletswas a practical objective. Test boards, previously examined forresidual solvents, were placed on a flat surface and treated witha measured volume of one or more solvents. After all tracesof the solvent(s) had disappeared, by evaporation or migrationinto the PCB matrix, spiked boards were stored open to ambientair in a laboratory or office isolated from chemical storage anddispensing operations. These boards were then examined over aperiod of several months to determine the potential for residualsolvent retention and detection over an extended time period.

Breadboard Gas Chromatography System

Analysis was based on the cryogenic collection of volatiles inthe purge gas stream followed by chromatographic separationusing a Hewlett-Packard (HP [Little Falls, New Jersey]) 5890Series II GC fitted with an HP 63Ni or Valco 140BN ECD([Houston, Texas]). Chromatograms were recorded using a HP3396B recording integrator. Selected circuit board samples werereexamined to confirm residual solvent identity employing aVarian Instruments Saturn 4D ion trap mass spectrometer (MS)(Walnut Creek, California). Data from these confirmatory exper-iments were recorded and processed using Saturn GC/MS workstation software (Version 5.41) and a Dell Optiplex GX1 (RoundRock, Texas) computer. As illustrated in Figure 1, the basic an-alytical system consisted of a sample container (new, uncoated,1-gallon metal paint can fitted with a Swagelok [Solon, Ohio]bulkhead union), associated purge gas flow system, cryotrap, andGC. Ultrahigh-purity helium was passed through a purificationsystem (high capacity gas purifier, Supelco 23800-U [St. Louis,Missouri], with purifier tube, 22396) before entering a Swageloktee to feed both the purge and carrier gas streams. Purge gas(20 mL/min) from the sample container was passed through aU-tube trap (nickel, 1/16 inch outer diameter, 0.040-inch in-ner diameter, 50-cm length) immersed in a liquid nitrogen-filledDewar to trap and concentrate volatiles released from circuitboard samples. Purge gas flow was measured with a mass flowmeter and periodically confirmed using a bubble flow meterwhile a helium leak detector was used to confirm the absenceof leaks. At the end of the collection period (20 to 100 minutesduring the method development phase of this work), the in-line6-port valve (Valco Instruments, D6UWE) was rotated to theinject position to divert carrier gas flow through the trap, which

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322 R. N. Lee and B. W. Wright

Figure 1. Schematic illustration of the breadboard residual solvent analysis system.

was removed from the liquid nitrogen bath, and allowed to warmto room temperature to permit transport of the collected ana-lytes to the GC. The capillary GC column (Supelco SPB-624column, 30 m × 0.25 mm, df = 1.4 µm, Cat. No. 24255) washeld at –20◦C during the 3-minute transfer period before initiat-ing the temperature program, –20◦C (0.0-min hold) followed by10◦C/min to 80◦C (0.0-min hold) and then 20◦C/min to 205◦C(4.0-min hold), for separation and detection of collected sol-vents. Sample components were identified by their retentiontimes determined from the analysis of external standards andfrom internal standards (chloroform, TCE and PCE) consistentlyobserved at measurable levels as a consequence of ambient aircontamination. Use of an ECD permitted selective and highlysensitive detection (10–100 femtogram range) (Agilent Tech-nologies, 2001) of halocarbon solvents free of interference fromother organics present in the circuit board matrix.

Dedicated Ozone-Depleting Compound Gas Chromatograph

Initial experimental work with the breadboard system demon-strated the feasibility of the analytical approach. Follow-on work

served the dual purpose of assembling a dedicated ODC chro-matographic system offering computer control of the analy-sis and completing development of an SOP defining both theanalysis conditions and associated quality-control procedures.The dedicated system used an Agilent 6890N (Wilmington,Delaware) gas chromatograph equipped with a micro ECD, aheated internal gas valve (Valco D6UWE) and electronic pres-sure/flow control modules for all gas flows. Agilent ChemStationA.09.03 software was used for GC control and data acquisition.This system fulfilled the objective of constructing a tool for as-sessing and confirming compliance with ODC regulations. Allexperiments with the dedicated system were conducted with ameasured purge gas flow of 20 mL/min. Other parameters, suchas the purge gas collection time and elevated temperature usedto accelerate residual gas release from the PCB, were recordedbut varied from sample to sample. To provide evidence for thelong-term retention of residual solvents by circuit board matri-ces and yield chromatographic data well above analyte detec-tion limits, purge gas collection times were extended to samplevolumes of up to 2 L. The ability to examine a variety of sam-ple volumes and range of temperatures provided the flexibility

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required to demonstrate successful application of the method.Once the basic approach and system components were iden-tified, the dedicated ODC GC system was assembled and theoperational conditions fine-tuned to yield a procedure that in-corporated effective calibration and quality assurance measures.Design of the dedicated ODC GC system included the use of aTedlar bag housed in a thermostated enclosure (ThermoSafeStorage [Arlington Heights, Illinois] container, PPA422, 0.9 cuf. heated with a 10 inch × 2 inch 100 watt silicone rubber heater)to serve as the sample (circuit board) container. Tedlar bags wereconditioned before use by warming to 45◦C while flushing withultra high purity helium at 20 mL/min for at least 24 hours.

Finally, a significant design objective for the dedicated ODCGC system was to simplify field operation by reducing cryogenconsumption. This was accomplished with the adoption of a 25 m× 0.32 mm id, df = 10 µm CP-PoraPLOT Q porous layer opentubular (PLOT) column (Varian Instruments CP7551) as the an-alytical column. During the course of performance tests, a modi-fied version of this column that replaced the particle layer with anintegrated porous layer was examined and introduced as the ana-lytical column (a 25 m × 0.25 mm id, df = 3 µm CP-PoraBONDQ, Varian Instruments CP7348). These columns eliminated theneed for sub-ambient column temperatures to achieve efficientcapture of analytes transported from the cryogenic trap to theanalytical column during sample injection. (Specific operatingconditions are listed in Table 1.) Subsequent work includedthe construction of a second P&T GC system, equipped with

Table 1. Purge-and-trap and gas chromatography parameters for theanalysis method.

Purge and trap parameters

Samplechamber

temperature,◦C

Numberof purgeand trapsamples

Nominalpurge

gas flow,mL/min

Samplecollectiontime, min

Nominalsample

volume, mL

Room temperature ≥ 2 20.0 10.0 200(∼20–23)35 �2 20.0 10.0 200

Gas chromatography method parameters

CP-PoraBOND Q 25 m,250 µm ID,

Column df = 3.0 µ

Initial temperature 30◦CInitial time 11.0 minutesRate 1 100◦ C/minFinal temperature 80◦CTime 0.0 minutesRate 2 8◦ C/minFinal temperature 224◦CTime 6.0 minutesTotal analysis time 35.5 minutesGas sampling valve temperature 100◦CInitial Column head pressure 16 psiCarrier Helium, constant flowPurge gas pressure 20 psiElectron capture detector 250◦C

temperature 250◦

a column (Quadrex [Woodbridge, Connecticut] 007–624, a 30m × 0.32 mm id, df = 5.0 µm cyanopropylphenyl polysilox-ane stationary phase) having different retention characteristics toprovide confirmation of residual solvent identification. The tem-perature program for this column was −20◦C (3.0 min hold) fol-lowed by 100◦C/min to 30◦C (0.0 min hold) and then 10◦C/minto 200◦C (4.0-min hold). System and operational modifications,tested to demonstrate performance, were then incorporated intothe analysis methodology, which was applied to the examinationof boards removed from new electronic products purchased forthis study.

Results and Discussion

Chromatographic profiles obtained from circuit board analysis,using the P&T GC systems described in this study, are generallyquite simple, showing no more than 10 measurable peaks. Typi-cal output, shown in Figure 2, displays overlaid chromatogramsobtained using the Quadrex 007–624 column from consecutivepurge gas samples acquired at room temperature and then at35◦C during the analysis of a PCB removed from a new elec-tronic product. Successful application of the P&T techniquerested on the elimination of background contamination contri-butions to the analytical process. All analyses presented in thisstudy were supported by blank measurements, described later intext, and adopted as essential components of the methodologyand the SOP. Before describing experiments that demonstratethe feasibility, and ultimately, the successful application of aP&T procedure for detection of residual solvents in PCBs, workis described relating to selection of the sample container andthe collection/analysis of various “blank” samples confirmingsystem integrity and cleanliness. This discussion is followed bythe presentation of studies performed with a variety of new andaged PCBs and concludes with the analysis of PCBs from newelectronic products.

Purge and Trap Analysis Procedure

The PCB analysis procedure consisted of a series of P&T sam-ples designed to distinguish between solvents absorbed in thePCB matrix, and contributions from: 1) solvents adsorbed onthe PCB surface from ambient air, and 2) from ambient airpresent in the container that is only partially removed by purgegas flow before collection of purge gas sample. Initial sampleswere collected with the circuit board at room temperature be-fore warming the PCB enclosure, using a resistance heater, toaccelerate the release of residual solvents from the circuit boardmatrix. This P&T method was tested by examining older andcurrent commercial circuit boards, spiked and unspiked, usingthe breadboard system. Purge gas flow rates and sample collec-tion times were recorded for individual P&T samples and thetotal sample volume calculated. Analyte peak areas measuredby the data system were then divided by the corresponding sam-ple volume to give volume normalized peak areas. The relativepeak area of analytes detected in the respective P&T samples isdefined as the volume normalized peak area (VNA) divided by

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Figure 2. Overlaid chromatograms recorded for purge gas samples collected with a circuit board at room temperature and 35◦C.

the average VNA of that analyte in P&T samples collected fromthe PCB sample at room temperature:

VNAx (1)

Relative peak area = VNAx/average VNAroom temp, where x isthe purge gas sample number.

Relative peak area data were then plotted for the analysisseries, and residual solvents were designated from their responseto temperature changes in the PCB sample container. Criteria forresidual solvent designation and procedures for evaluating dataquality are addressed in the following section.

Blanks

Before analysis of PCB samples, instrument blanks and systemblanks were taken to confirm system cleanliness by examiningpotential contamination routes that would compromise analyti-cal results. Instrument blanks included cryogenic collection ofpurge gas acquired during experiments in which purge gas flowby-passed the sample container. System blanks were obtainedby cryogenic collection of purge gas passed through the emptysample container, at both room temperature and elevated tem-peratures, to evaluate potential contamination via analyte releasefrom container walls. Instrument blanks consistently demon-strated the delivery of high purity helium to the GC systemas evidenced by the absence of chromatographic peaks. Whenpassed through an empty paint can, trace levels of prominentambient halocarbons (notably chloroform, TCE, and PCE) weregenerally observed as a consequence of incomplete air removalover a relatively short pre-analysis purge time of 30 to 60 minutesand/or release of these chemicals from container walls. VNAsof sample components associated with ambient air remained es-sentially unchanged in sequential P&T samples, regardless ofthe container temperature, when a new, unused paint can servedas the sample container.

Purge gas data from system blanks (empty PCB con-tainer) were tracked as relative peak area, by comparing VNAs(VNAsample/average VNAroom temp) over the analysis sequence.Larger VNAs correspond to higher levels of released analytesand a rapidly rising VNA as a function of temperature suggestsmore rapid release and/or diffusion from the PCB matrix. Rel-ative peak area data for detected analytes in purge gas samplesfrom empty Tedlar bags are shown in Figures 3a and 3b. In Fig-ure 3a, purge gas samples were taken with the bag at both roomtemperature and after warming it to 35◦C. In contrast, Figure 3bpresents data for an experiment in which the Tedlar bag was heldat room temperature. Examination of data displayed in Figure3a shows a slight increase in non-ODC analyte peak areas at35◦C. The observed influence of temperature on analyte peakareas, which is consistent with analyte release from interior bagsurfaces, decreases with the length of the conditioning time.It should be noted that no ODC solvents have been observedin purge gas samples from new or thermally conditioned Tedlarbags. In effect, the data in Figure 3a demonstrate that the thermalconditioning process was effective in eliminating contaminationfrom the Tedlar bag.

In addition to verifying the absence of ODC release fromTedlar bags, the analysis of empty bags (system blanks) pro-vides the statistical foundation for determining the level at whichthermally desorbed residual solvents can be considered greaterthan the background. From statistical process control techniques(Zwillinger, 1996), a measurement is considered to be withinthe normal (expected) variation for a population if the variabil-ity is within three standard deviations of the average baseline.Test measurements outside this range are considered abnormal.Hence, from a statistical basis, the minimum peak area thresh-old for a residual solvent to be considered present at the warmtemperature measurement (35◦C) would be three times the stan-dard deviation of the measurement at room temperature. Therelative peak areas and the respective standard deviation data

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Empty Tedlar Bag #44

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1 2 3 4 5 6 7

Purge Gas Sample Number

Rel

ativ

e P

eak

Are

aCHCl3

TCE

PCE

~23oC

~23oC ~23oC

~23oC

35oC

35oC

35oC

Empty Tedlar Bag #39 at Room Temperature

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 2 3 4 5 6


Rel

ativ

e P

eak

Are

a

CHCl3

TCE

cis-1,3-DCP

trans-1,3-DCP

PCE

(a)

(b)

Figure 3. Relative peak area plots for analytes detected in purge gas samples taken from an empty conditioned Tedlar bag: a) Tedlar bag at roomtemperature and then after warming to 35◦C; b) Tedlar bag at room temperature (∼23◦C).

from the empty Tedlar bag analyses shown in Figure 3b arelisted in Table 2. The largest standard deviation of 0.23 was ob-served for cis-1,3-dichloropropene (DCP). Consequently, mea-surements giving a relative peak area greater than 1.7 times the

baseline (1.0) would be considered significant. However, inthis work a more conservative operative threshold of at leastthree times the baseline (average volume normalized peakarea for purge gas samples with the empty container at room

Table 2. Relative peak areas for purge gas samples from empty Tedlar Bag #39.

Compound Purge gas samples relative peak area Average Standard deviation

CHCl3 1.060 0.884 0.905 1.221 0.974 0.956 1.000 0.125Trichloroethene (TCE) 0.902 0.986 0.795 1.183 1.085 1.049 1.000 0.138cis-1,3-dichloropropene (DCP) 0.794 0.940 0.770 1.392 1.084 1.015 1.000 0.227trans-1,3-DCP 0.826 1.007 0.857 1.138 1.065 1.107 1.000 0.131Tetrachloroethene (PCE) 0.839 0.995 0.905 1.036 1.183 1.091 1.000 0.127

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Figure 4. Photograph of circuit board sample in a Tedlar bag container.

temperature) was arbitrarily chosen. Although analyte peak areadata displayed in Figure 3a suggest the release of non-ODC ana-lytes from a thermally conditioned Tedlar bag, the magnitude ofthe change in relative peak areas is within the measurement win-dow derived from statistical process control techniques and wellwithin the conservative operative threshold of 3.0 applied duringthis study. Although these results support the use of Tedlar bags,potential contamination concerns stress the need to characterizeall Tedlar bags before use and reuse for PCB analysis; a pro-cess incorporated into the SOP and rigorously applied duringthe performance of work reported here.

Sample (Printed Circuit Board) Containers

As illustrated in Figure 1, work with the breadboard system wasconducted using a 1-gallon paint can as the sample container.Although a paint can offered a significant advantage in terms oflow potential surface contamination that might contribute to theECD signal and threaten sample cleanliness, the relatively largedead volume and occasional sealing problems were distinct dis-advantages that extended the analysis time. Following work withthe breadboard system, the use of Tedlar bags was investigatedas an alternative container.

The use of Tedlar bags for the sample container offered theadvantage of reduced dead volume, but tests were required toverify leak-free service, the absence of interfering solvents in theTedlar matrix and memory effects that would prohibit their reuse.During early tests with the breadboard system, Tedlar bags hadbeen considered but were rejected due to observed out-gassingchemicals (non-ODC) from interior walls and frequent failureto demonstrate leak free performance. As discussed previously,subsequent tests with Tedlar bags demonstrated that out-gassingcontamination problems were overcome by thermally condition-ing before use. Other concerns, such as the ability of Tedlarbags fitted with a Swagelok union to provide a leak-tight enclo-sure, were resolved by investigating bags from several suppli-

ers. Those tests identified a supplier offering consistently supe-rior performance (Jensen Inert Products [Coral Springs, FL]).In practice, all Tedlar sample bags were conditioned before useand evaluated again before their reuse to confirm leak-free per-formance and the absence of memory effects due to analyteretention. Figure 4 shows the sealing mechanism and the circuitboard/Tedlar bag container in-place during P&T experimentswith the dedicated ODC GC. After inserting the PCB, the openend of the bag is folded over itself and sealed using a clampconstructed with an aluminum bar (0.125′′ × 0.75′′) cut to thelength of the Tedlar bag opening and the bolts tightened to com-press the fold. Advantages inherent in the use of pliable samplebags included being able to select a sample bag size to best fiteach PCB, as well as the ability to flatten the sample bag aroundthe board and position the clamp seal to minimize bag volume.Reducing the amount of dead volume reduced the pre-analysispurge times required for each PCB sample. All data reportedfor circuit boards removed from new commercial products wereacquired using a Tedlar bag container.

Breadboard System

Spiked Circuit Boards.Circuit boards selected for solvent spiking were purchased

as replacement boards for laboratory equipment. They werefabricated, without the use of restricted solvents, using clean-ing solvents identified by the manufacturer (diethylene glycol,monobutyl ether, monoethanolamine and diethanolamine) andstored after receipt in an office at PNNL (Richland, Washing-ton) where exposure to ambient solvent vapor contaminationwas minimal. These boards were characterized using the P&Tprocedure before liquid exposure to selected ODC or industrialsolvents to simulate a cleaning process. Data from the analy-sis of one of these boards are summarized in Figure 5. Resid-ual solvents associated with this circuit board were identifiedby the P&T analysis series starting at room temperature and

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Unspiked Circuit Board

0

3

6

9

12

15

1 2 3 4 5 6


Rel

ativ

e P

eak

Are

a

CH2CCl2

unknown

CHCl3

CCl4

TCE

PCE38oC

40oC

20oC 20oC

46oC

20oC

Figure 5. Relative peak area plots versus purge sample number for a circuit board known to be fabricated without the use of ozone depleting chemicals.

then warming to 46◦C. Two of the higher concentration sol-vents were identified as prominent industrial solvents that areoften observed in P&T analyses of PCB samples (chloroformand TCE). The retention time of a third analyte did not matchany ODC or halocarbon standard available in our laboratory.Since none of these solvents were identified by documentationreceived from the vendor, their presence suggests introductionfrom components soldered to the board, or as residues from sub-strate polymerization in forming the circuit board matrix, andnot directly related to the circuit board cleaning process.

The three spiked boards used for residual solvent detectionexperiments are described in Table 3. Since the low milliliterquantities of solvent used to spike these boards were consider-ably lower than would be expected from a cleaning operation,analyte detection in the aged samples represented a significantchallenge. Spiked boards were removed from storage two to fourtimes over a period of approximately 5 months to evaluate theability of the proposed P&T technique to successfully detectresidual solvents over an extended period of time. During eachexamination, data were acquired by sampling at room temper-ature before repeating the analyses at a higher temperature. Allanalytes spiked on the board were detected during subsequentP&T analyses. Consistent with their release from the circuitboard matrix, volume normalized peak areas increased with thetemperature of the container holding the circuit board. While

Table 3. Circuit boards spiked with volatile solvents.

Circuit Solvent Last analysisboard Solvent(s) volume, mL (age, days)

1 CHCl3, CH2Cl2, CFC-113 2.5 ea 1462 HCFC-141b 1.3 1483 CH2Cl2 1.8 140

CFC-113, 1,1,2-trichloro-1,2,2-trifluoroethane; HCFC, hydrochlorofluoro-carbon.

the periodic analysis of spiked boards was not conducted un-der uniform conditions, since purge gas collection times andthe temperature of the circuit board were not tightly controlled,the amount of analyte found decreased over time. However, de-spite brief exposure of these circuit boards to low volumes ofvolatile solvents, successful detection of these chemicals aftera 5-month aging period provided strong evidence for the feasi-bility of detecting residual solvents. Data acquired from board#1, after an aging period of 146 days, are plotted in Figure 6.Residual methylene chloride, chloroform, and CFC-113 that hadbeen spiked onto the circuit board were all detected when thetemperature of the circuit board sample was raised from roomtemperature to 45◦C. In the same way, data from circuit board#2, spiked with the ODC replacement solvent hydrochlorofluo-rocarbon (HCFC)-141b, shown in Figure 7, also demonstratedsubsequent detection after an extended aging period. During thefinal analysis, after aging 148 days, the analyte was not detectedin purge gas with the circuit board sample at room temperaturebut appeared in subsequent samples (five through seven) whenthe circuit board enclosure was heated to a moderate 39◦C. Sincedetection of residual solvents is dependent on their rate of re-lease from the circuit board matrix, failure to detect a distinctHCFC-141b peak in room temperature samples was simply in-dicative of its low concentration. In this instance, temperaturedriven concentration changes associated with the spiked residualsolvent are displayed by plotting the volume normalized peakareas of the HCFC-141b peak in the respective purge gas sam-ples. Analysis of circuit board #3, spiked with methylene chlo-ride, also demonstrated successful detection of this volatile sol-vent after an aging period of nearly 5 months (data not shown).

Aged Commercial Circuit BoardsIn addition to examining spiked circuit boards to verify the

detection of residual solvents in boards over an aging period ofseveral months, the analysis procedure was also evaluated by

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Methylene Chloride, Chloroform and CFC-113 Spiked Circuit Board, Day 146

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Figure 6. Relative peak area plots of solvents detected in purge gas samples from a circuit board 146 days after spiking with methylene chloride,1,1,2-trichloro-1,2,2-trifluoroethane [CFC-113], and chloroform.

examining circuit boards removed from retired laboratory andoffice equipment. Although the age and history of these boardscould not be fully documented, all were estimated to be in excessof 5 years old at the time of analysis (2001) and, by virtue ofknown histories, had no exposure to solvent vapors in excessof ambient air concentration levels after arrival at PNNL. Theonly halocarbon solvent stored and routinely used in the buildingwhere these boards were used, and this work was conducted, wasmethylene chloride. At least one residual solvent was detectedin all samples examined. This significant finding indicates longterm release of solvent at levels sufficient for detection in purgegas samples is feasible. Residual solvents detected in five aged

circuit board samples are reported in Table 4. Relative peakarea data acquired from the corresponding P&T experimentsconducted with each of these circuit boards are presented inFigures 8a–8e. Each of these plots is characterized by two ormore solvents showing a significant increase in the relative peakarea (�3) when the temperature of the circuit board subjectedto P&T analysis was increased. ODC solvents CFC-113 andmethyl chloroform were individually detected in circuit boardsremoved from two different laboratory instruments.

Following analysis using the GC/ECD based P&T procedure,several boards were also examined by replacing the ECD witha Varian ion trap MS. Despite the inherently lower sensitivity

HCFC-141b Spiked Circuit Board, Day 148

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Figure 7. Relative peak area plots of solvents detected in purge gas samples from a circuit board 148 days after spiking with hydrochlorofluorocarbon(HCFC)-141b.

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Table 4. Residual solvents detected in circuit boards removed from old laboratory and office equipment.

Residual Sample Purge gas flow, Sample collectionProduct PCB solvents detected temperature, ◦C mL/min time, min

Office computer TCE 20 (two at room temperature) 19.8, 20.0 50.0, 50.0PCE 38 21.0 50.0

40 20.9 50.042 21.2 50.0

Videocassette recorder PCE 20 (five at room temperature) 19.5, 19.3, 19.7, 19.5, 18.8 45, 45, 46, 46, 51TCE 37 20.2 41

CHCl3 43 20.7 4142 19.6 72

Laboratory instrument TCE 21 (three at room temperature) 19.6, 19.6, 19.5 51, 51, 56CHCl3 36 21.6 51PCE 42 21.4 51

CFC-113 45 21.8 54CCl2CH1

2Printer CHCl3 21 (two at room temperature) 18.8, 18.9 57, 57

TCE 39 20.7 60PCE 43 20.0 60

CH2Cl2 45 20.3 30Laboratory instrument CHCl3 21 (three at room temperature) 18.9, 19.3, 19.4 72, 72, 72

TCA 43 20.8 7346 20.2 7848 20.6 72

Ozone-depleting compound solvents are underlined. Test results are plotted in Figure 8. CFC-113; 1,1,2-trichloro-1,2,2-trifluoroethane;PCB: printed circuit board; PCE: tetrachloroethene; TCA: 1,1,1-trichloroethane; TCE: trichloroethene.

of this detector relative to the ECD, the ion trap providedan independent, alternative set of measurements to evaluateGC/ECD data. However, since the capture of residual solventsfrom circuit board matrices yields only trace amounts of sol-vent (sub-picogram to picogram amounts per liter of purgegas), this approach was able to identify only the most abun-dant chemicals present in these samples. Where residual sol-vent concentration levels were sufficiently high, GC/MS dataconfirmed GC/ECD results. For example, Figures 9a and 9b re-port the volume normalized peak areas for analytes detectedin one of the circuit boards subjected to GC/ECD and GC/MSanalysis, respectively. Of the three solvents found to be asso-ciated with the circuit board from the GC/ECD results, TCEwas the only solvent present at a sufficiently high concentra-tion to be identified by GC/MS analysis. Overlaid extracted ionchromatogram peaks (m/z 95) for residual TCE are shown inFigure 10 for analyses at room temperature and 37◦C. This fig-ure includes an inset showing the mass spectrum for the ana-lyte corresponding to this peak and confirming its identity asTCE.

Off-the-Shelf Circuit Boards.To obtain current product samples, imported circuit boards

sold for computer system applications were purchased (2002)from a local supplier. These boards were analyzed using theGC/ECD P&T procedure. Table 5 summarizes residual solventsidentified in these circuit boards; no ODCs were detected byP&T analysis.

Dedicated Ozone-Depleting Compound–Gas-ChromatographySystem

Operation of the breadboard system utilized for the experi-ments described previously relied heavily on operator super-vision and control. This approach provided the flexibility re-quired to explore a range of operational parameters to enhanceanalyte detection. For example, while purge gas flow was held at20 mL/min, sample volumes were adjusted by varying samplecollection times to permit analyte concentration from purge gassample volumes that often exceeded 1 L. Other parameters, suchas the temperature of the sample enclosure, were also varied toenhance residual analyte release and detection. Construction ofthe dedicated ODC GC and the development of a SOP wereaccompanied by further examination of the P&T parameterswhile employing circuit boards removed from a variety of com-mercial products to assess system performance. To reduce sam-ple turnaround time, operational conditions were refined duringthis process to minimize the length of purge gas sampling and

Table 5. Residual solvents identified in computer-related circuitboards purchased from a local electronics outlet.

Sample Residual solvents identified

1 TCE, methylene chloride2 TCE, chloroform, PCE3 TCE, methylene chloride

PCE: tetrachloroethene; TCE: trichloroethene.

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TCA

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TCE

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VCR Circuit Board

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(a) (b)

Circuit Board from a Laboratory Instrument

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Printer Circuit Board

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21oC21oC

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(e)

Circuit Board from a Laboratory Instrument

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CH2Cl2

CHCl3

TCA

CCl4

TCE

PCE

21oC 21oC 21oC

46oC

48oC

43oC

Figure 8. Relative peak area plots of solvent peaks observed in purge and trap experiments with aged circuit boards. Data are plotted for a series of purgeand trap samples for the respective circuit boards at room temperature before increasing the container temperature. Circuit board samples: a) circuit boardfrom a personal computer, b) circuit board from a videocassette recorder, c) circuit board from a laboratory instrument, d) circuit board from a printer, e)circuit board from a second laboratory instrument. Results and analysis conditions are summarized in Table 4.

GC run times. As in previous studies, the initial circuit boardtemperature was room temperature (∼20◦C–23◦C), followed byraising the enclosure temperature to 35◦C or 45◦C to acceler-ate release and enhance residual solvent detection. In additionto examining a range of P&T operating conditions, column op-tions and GC parameters were investigated during dedicated GC

system development. While breadboard system tests employedsub-ambient column temperatures to ensure the capture of an-alytes in a narrow band at the front of the analytical column,design specifications for the dedicated ODC GC targeted aninitial column temperature of 30◦C. This feature enhanced an-alyzer flexibility for laboratory and field operation by reducing

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CHCl3

PCE

TCA

20oC20oC

37oC

20oC

41oC

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20oC


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TCE, m/Z 95

CH2Cl2, m/Z 84

20oC 20oC

35oC

20oC

37oC

32oC

(a)

(b)

Figure 9. Relative peak area plots detected for analytes found in purge gas samples subjected to analysis by: a) gas chromatography/electron capturedetector (GC/ECD), and (b) GC/mass spectrometry (MS) single ion chromatograms for m/Z 95 (trichloroethene [TCE]) and m/Z 84 (CH2Cl2).

cryogen consumption. This objective was accomplished withthe use of a porous layer open tubular (PLOT) capillary column.Consequently, all results reported in this section, except thoseassociated with the confirmatory analysis method, were obtainedwith a PoraPLOT Q or PoraBOND Q capillary column.

Portable Radio Circuit BoardAmong the electronic products purchased for removal and

examination of PCB components was a small portable radio.This device contained a single circuit board that was removedand placed in a Tedlar bag that had been conditioned and char-acterized by the P&T procedure before circuit board analysis.Purge gas sample volumes for the respective sample injections

were 945, 945, 987, 483, and 525 mL. Relative peak area datafrom analysis of this PCB, shown in Figure 11, identify 1,1,2-trichloroethane as the primary residual solvent. Other halocar-bons, including the ODCs TCA (1,1,1-trichloroethane) and car-bon tetrachloride, were also identified as residual solvents fromthe examination of data displayed in this Figure. Preliminarydesignation of residual solvents (those meeting relative peakarea criteria) may be obtained from a simple visual inspectionof overlaid chromatograms generated from purge gas samplesobtained with the circuit board at room temperature and at an el-evated temperature. For example, Figure 12 shows overlaid chro-matograms corresponding to purge gas samples three and fourfrom P&T analysis of the portable radio PCB. The magnitude

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Figure 10. Overlaid single ion chromatograms (m/Z 95) for TCE peak with circuit board sample at 20◦C (chromatogram A) and 37◦C (chromatogramB). Insert shows mass spectrum of the corresponding analyte, which identifies it as trichloroethene (TCE).

of the 1,1,1-trichloroethane peak and its increase at the higherpurge gas temperature demonstrates the dominance of this resid-ual solvent released from the circuit board. The inset shows anexploded view of other solvent peaks, including ODCs TCA(1,1,1-trichloroethene) and carbon tetrachloride, designated asresidual solvents by virtue of the effect of temperature on theirrespective peak areas. Visual inspection of chromatograms doesnot replace the use of relative peak area data in designating resid-ual solvents but is shown here to assist the reader in visualizingand understanding test results. Likewise, rigorous identification

of chromatographic peaks is based on matching defined reten-tion time windows.

Television Set Circuit BoardsTwo circuit boards were removed from a new television set for

inspection using the P&T procedure to identify solvents asso-ciated with PCB fabrication. Since these analyses preceded theformulation of a common set of P&T conditions, sample collec-tion time and purge gas flow were recorded for each sample topermit calculation of volume normalized peak areas. Purge gas

Portable Radio Circuit Board

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HCFC-141b

HCFC-225ca

CHCl3

TCA

CCl4

TCE

CHCl2CH2Cl

CHCl2CHCl2

18oC18oC

45oC

45oC

18oC

Figure 11. Relative peak area plots of detected analytes in purge gas samples obtained with a circuit board from a portable radio. Chromatograms obtainedfor the third and forth purge gas samples are shown in Figure 12.

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Figure 12. Overlaid chromatograms from the injection of purge gas samples collected with the circuit board at 18◦C (purge gas sample 3) and 45◦C(purge gas sample 4). The inset shows the chromatograms plotted on a more sensitive scale.

TV Circuit Board #1

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Figure 13. Relative peak area plots of observed analyte peaks with the circuit board samples from a television set: a) board 1: Purge gas sample volumeswere 357, 441, 462, 273, and 378 mL; b) board 2: Purge gas sample volumes were 420, 420, 441, and 462 mL.

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flows averaged 21 mL/min and total sample volumes for circuitboards #1 (273–462 mL) and #2 (420–462 mL) were determinedby the length of the sample collection period. Analytical results,generated from a series of P&T samples are summarized forboards #1 and #2 in Figures 13a and 13b, respectively. Theseplots, which display relative peak area versus sample number,identify TCE and chloroform as the prominent residual solventsassociated with both circuit boards. Although the ODC car-bon tetrachloride was observed in both sets of purge samples,concentrations were essentially independent of circuit boardtemperature (VNA45C/VNART < 2); a result that does not sup-port confident designation of this chemical as a residual solvent.This observation emphasizes the need to base residual solvent

designation on a series of P&T samples acquired at both roomtemperature and at an elevated temperature.

Clock Radio Circuit BoardsThe final set of circuit board samples were examined with

the dedicated ODC GC operated under the conditions definedby the SOP and summarized in Table 1. Under this method,purge gas flow continued to be 20 mL/min while P&T samples,collected with a sample loop immersed in liquid nitrogen, wereinjected for analysis after a 10-minute sampling interval. Initialsamples, taken after purging ambient air from the Tedlar bagenclosure for at least 30 minutes, were collected with the samplecontainer at room temperature (∼20◦C–23◦C) before raising the

Clock Radio, Small Circuit Board

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Clock Radio, Large Circuit Board

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Figure 14. Relative peak area plots from purge and trap samples from circuit boards from a clock radio purchased in January 2005: a) small board, andb) large board.

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sample temperature to 35◦C. Results displayed in Figures 14aand 14b summarize relative peak area data for detected analytesfrom P&T analysis of the two circuit board samples. These dataidentify the ODC TCA as a residual solvent associated with bothcircuit boards. Non-ODC solvents identified with these boardsincluded 1,1,1,2-tetrachloroethane, TCE, and chloroform.Purge gas volumes ranging from 221 to 245 mL were collectedfor the small circuit board (Figure 14a). Purge gas volumeswere reduced to 7 mL for the large board (Figure 14b) due tothe significant quantity of residual solvent released by this PCBat room temperature. Peak heights in overlaid chromatogramsfor both circuit board samples, shown in Figures 15a and 15b,clearly indicate TCA (a class II ODC solvent) as the prominentresidual solvent peak associated with both circuit boards.

Confirmatory AnalysisDevelopment and testing of the residual solvent analysis

method described previously utilized a single chromatographiccolumn and analyte identifications were based on matching re-tention times to those obtained from standards (typically withina 0.015-minute window). Although samples examined duringthe course of this work were characterized by relatively sim-ple analyte profiles, less than 10 detected analytes, a confirma-tory analysis method employing a second independent analysiswith a column possessing different retention characteristics wasneeded to verify residual solvent identification. Relative ana-lyte peak area plots for the confirmatory analysis of the clockradio large circuit board are displayed in Figure 16. Overlaidchromatograms acquired from reanalysis of this circuit board

Figure 15. Overlaid chromatograms of purge and trap samples obtained at room temperature (purge gas sample 2 in Figure 14) and at 35◦C (purge gassample 3 in Figure 14) from clock radio circuit boards: a) small board, and b) large board.

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Clock Radio, Large Circuit Board

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Figure 16. Relative peak area plots for the reanalysis of the large circuit board from a clock radio purchased in January 2005 using the confirmatoryanalysis method. Purge gas sample volumes were 235, 225, 227, and 224 mL. Overlaid chromatograms for purge gas samples two and three are shownin Figure 2.

using the Quadrex 007-624 column are shown in Figure 2. Con-sistent with the initial analyses using the PoraBOND Q column,these results identify the ODC TCA (1,1,1-trichloroethane) and1,1,1,2-tetrachloroethane as the primary residual solvents asso-ciated with this circuit board (see Figures 14b and 15b). Sincereanalysis was conducted nearly two years after the initial anal-ysis, these results not only provide confirmation of residual sol-vent identification but demonstrate residual solvent retention bythe circuit board over a period of more than 2 years. Applicationof the confirmatory analysis method to the reanalysis of morethan 10 different PCBs from new electronic products after ap-proximately 2 years has, in all cases, demonstrated agreementwith initial residual solvent identifications.

Detection LimitsAlthough the developed procedure was not designed to quan-

tify the residual solvent load, detector sensitivity measurementswere undertaken to provide an order of magnitude estimate of an-

Table 6. Detection limits for selected solvents using thededicated ozone-depleting compound gas chromatography.

Detection On-columnAnalyte limit, fg∗ injection, fg RMS S/N∗∗

CFC-113 10 50.0 24TCA 3 3.2 4PCE 2 31.0 70Carbon tetrachloride 3 20.0 441,1,2-trichloroethane 200 1800 21

∗Calculated for a signal-to-noise ratio >3 from visual inspection ofpeak heights and baseline noise.∗∗Calculated using Enhanced Data Analysis software, Agilent Chem-Station G1701DA D.02.00 SP1 (Santa Clara, California).CFC-113: 1,1,2-trichloro-1,2,2-trifluoroethane; PCE: tetrachloroeth-ene; TCA: 1,1,1-trichloroethane.

alyte levels in the purge gas stream. This was accomplished by re-configuring the GC for sample introduction through the splitlessinjection port. Serial dilution of stock analyte solutions in pen-tane to the sub-picogram/µl range (femtogram levels of analyteper 1 µl injection) yielded samples approaching the quantitativedetection limit and these measurements were used to calculatethe on-column analyte mass corresponding to a signal-to-noise(S/N) ratio >3. Detection limit estimates for solvents frequentlyfound as residual solvents in circuit board samples are listed inTable 6 and are generally in the 10–200 femtogram (fg) range(10−15 g).

Conclusions

This work reports experimental work focused on the applicationof a modified P&T procedure for the identification of restrictedsolvents used in the production of consumer products such asPCBs. Initial experiments, performed with blank and solventspiked circuit boards, using a breadboard chromatographic sys-tem demonstrated the long-term retention of volatile solvents bythe polymeric circuit board matrix. Solvents, including HCFC-141b, methylene chloride, chloroform, and CFC-113, were de-tected in circuit boards spiked with small quantities of thesechemicals and examined over a 5-month period.

Subsequent experiments included aged circuit boards takenfrom electronic equipment that had been removed from service,as well as recently manufactured boards. These experimentsdemonstrated the continuing presence of residual solvents, suchas PCE, TCE, chloroform. and the ODCs, CFC-113 and TCA, inaged or off-the-shelf circuit boards. Some of these boards wereknown to be at least 5 years old. In addition to meeting key an-alytical objectives, tests with aged circuit boards demonstratedthe ultra-trace detection requirements (sub-picogram) demandedfor analyte detection. Given the detection requirements imposed

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by the task and the ubiquitous nature of many of the chemicals ofinterest, the experimental approach, based on a modified P&Tprocedure was developed and tested to differentiate betweensolvents traceable to the ambient environment and those derivedfrom the circuit board matrix.

Following successful demonstration of the modified P&Tprocedure, a dedicated chromatographic system was assembledfor laboratory and field use. System development incorporatedtests that identified columns that eliminated the need for sub-ambient column oven temperatures and demonstrated the suc-cessful use of Tedlar bags, conditioned and tested to verify theabsence of target analytes, to serve as the sample container. Workwith the dedicated chromatographic system led to the develop-ment of a SOP that defines system calibration and operation,quality control procedures and a confirmatory method for con-fident residual solvent identification. Finally, the variability ofbackground analyte peak areas in system blanks was examinedto determine statistically significant changes in the relative peakareas accompanying an increase in the circuit board tempera-ture. Application of the P&T system to examine circuit boardsremoved from off-the-shelf electronic products demonstratedsuccessful implementation of the P&T procedure, including theuse of a method based on a second GC column to confirm resid-ual solvent identification. Reanalysis after approximately 2 yearsusing the confirmatory method of PCBs previously determinedto have residual solvents demonstrated the continued presenceof the originally designated solvents and ODCs. Solvents iden-tified in circuit boards taken from products such as radios anda television set include TCE, PCE, 1,1,2-trichloroethane, chlo-roform, 1,1,1,2-tetrachloroethane, carbon tetrachloride (a classI ODC) and TCA (1,1,1-trichloroethane) (a class II ODC).

Acknowledgements

This work was supported by Internal Revenue Service (IRS)under an Interagency Agreement with the US Department ofEnergy (DOE) under Contract DE-AC05-76RLO 1830 with thePacific Northwest National Laboratory (PNNL). Battelle Memo-rial Institute operates the Pacific Northwest National Laboratory.The views, opinions, or findings contained within this report arethose of the authors and should not be construed as official po-sition, policy, or decision of the DOE or IRS unless designatedby other documentation.

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Appendix

The predicted and subsequent confirmation of stratosphericozone depletion has been linked to photodissociation of halocar-bons (e.g., chlorofluorocarbons [CFCs], hydrochlorofluorocar-bons [HCFCs] and chlorocarbons) in the stratosphere. An inter-

national agreement, the Montreal Protocol, was signed in 1987 inresponse to the projected severe environmental consequences ofthe expanding use of these chemicals (Ozone Secretariat, UnitedNations Environment Programme, 2006). This agreement de-fined the implementation of a regulatory plan for the phase-out and ultimate banning of ozone-depleting chemicals (ODCs).These chemicals, consisting of eight compounds, were selectedbecause of their high production levels and were separated intotwo classes in accordance with the magnitude of their ozone-depletion potential (ODP, calculated index of ozone destructionof a given chemical relative to an equal weight of CFC-11; classI compounds have an ODP > 0.2 and class II compounds have anODP < 0.2). Since1987, the Montreal Protocol has been modi-fied in response to increased understanding of the mechanism ofozone depletion, the anticipated contribution of a broader rangeof chemicals and the projected consequences of various regula-tory scenarios in reestablishing the ozone shield. Consequently,chemicals addressed by the protocol have been expanded toinclude compounds with high ODPs and/or significant globalwarming potential (GWP, predicted measure of a gas or va-por’s contribution to global warming relative to CO2). Phase-outschedules are now in place for a total of 56 compounds (15 CFCs,3 halons [haloalkanes, alkanes containing one or more halogenatom], 34 hydrobromofluorocarbons [HBFCs], carbon tetrachlo-ride, methyl bromide, chlorobromo methane and TCA). Addi-tionally, long-term production phase-out schedules are in placefor HCFCs introduced as CFC replacements. The developmentand production of new solvents and solvent mixtures continuesto represent an important component of the global response to ar-resting destruction of, and ultimately restoring, the stratosphericozone shield (United States Environmental Protection AgencySignificant New Alternatives Policy (SNAP) program). Repre-sentative industrial solvents and their respective ozone depletionand global warming potentials are listed in Table 7.

During this period of transition, implementing economic in-centives (United States Code, Code Section 4682(c)) and track-ing compliance to the scheduled phase-out built into the Mon-treal Protocol are key components of the strategy for reversingstratospheric ozone depletion. Economic incentives, which ad-dress both non-signature developing nations and signature na-tions (two categories, industrial or developing, based on theirrelative level of ODC emissions), include regulatory measuresthat apply to products produced with ODCs and assistance inmeeting phase-out objectives by providing technical assistancein eliminating their use. In the United States, regulatory mea-sures include production bans on high-use CFCs and the phasedelimination of CFC substitutes having a reduced but, neverthe-less, significant potential for stratospheric ozone depletion (USClean Air Act, as amended (42 U.S.C. 7401 et seq.). Regula-tory measures also extend to labeling requirements on electronicproducts, such as radios, manufactured with the use of ODCs,and the application of import duties on these products.

Industrial cleaning operations represented a significant ap-plication for ODCs before the implementation of environmentallegislation restricting their use. For example, precision cleaning,

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Table 7. Representative industrial solvents and their respective ozone depletion and global-warming potentials.

ODP1 (CFC, HCFC, United StatesCompound Formula CAS HFE, HFC) GWP2

100yrs regulation

ODC solventsCarbon tetrachloride CCl4 56-23-5 1.1 1,3803 Production ban, 1996TCA CH3CCl3 71-55-6 0.1 1443 Production ban, 1996CFC-113 CCl2FCClF2 76-13-1 0.8 6,0303 Production ban, 1996

ODC ReplacementsC1-C3 PFC CF4 75-73-0 0 >5,000

CF3CF3 76-16-4CF3CF2CF3 76-19-4

HCFC-225ca CF3CF2CHCl2 422-56-0 0.024 1203 TSCA listedHCFC-225cb CClF2CF2CHClF 507-55-1 0.034 5863 TSCA listedHCFC-141b CHCl2CH2F 1717-00-6 0.124 7133 Production ban, 2003HFE-7100 C4F9OCH3 163702-08-7 0 390

163702-07-6HFC-43-10mee CF3CF2CHFCHFCF3 138495-42-8 0 1,6103

Alternative solventsBP CBrH2CH2CH3 106-94-5 0 TSCA listedPCE CCl2CCl2 127-18-4 0 ∼ 10 TSCA listedTCE CCl2CHCl 79-01-2 0 <10 TSCA listedChloroform CHCl3 67-66-3 0 5 TSCA listedMethylene chloride CH2Cl2 75-09-2 0 103 TSCA listed1,1,2-Trichloroethane CCl2HCH2Cl 79-00-5 0 0cis and trans-1,3-DCP CHClCHCH2Cl 10061-01-5 0.002

10061-02-6trans-1,2-Dichloroethene CHClCHCl 540-59-0 0 01,1-Dichloroethene CCl2CH2 75-35-4 0 0

1. ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11.2. GWP is the ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide over a specified time period (timehorizon).3. ODP and GWP data were taken from the “IPCC/TEAP Special Report on Safeguarding the Ozone Layer and the Global Climate System: Issues Relatingto Hydrofluorocarbons and Perfluorocarbons, (de Jager et al., 2005).”Chemical Abstracts Services Registry number; CFC-113: 1,1,2-trichloro-1,2,2-trifluoroethane; CFC: chlorofluorocarbon; DCP: dichloropropene; GWP:global warming potential; HCFC: hydrochlorofluorocarbon; HFC: hydrofluorocarbon; HFE: hydrofluoroether; nBP: bromopropane; ODC: ozone-depletingcompound; ODP: ozone-depletion potential; PCE: tetrachloroethene; PFC: perfluorocarbons; TCA: 1,1,1-trichloroethane; TCE: trichloroethene; TSCA:Toxic Substance Control Act.

including defluxing operations in the production of electroniccircuit boards, was a significant application area for 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113). Since circuit boardproduction for the domestic electronics industry is dominated

by small suppliers, many of which are off-shore operations, theenvironmental legislation enacted in the United States imposesimport restrictions that require boards produced using controlledsubstances be identified.

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