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Agilent Ultimate Plus Fused Silica Tubing Technical Overview Introduction Deactivated fused silica tubing is widely used for guard columns, transfer lines, or long retention gaps in GC and GC/MS applications with heavy matrix, and for analysis of semivolatile compounds [1,2,3,4]. High inertness is a key requirement of tubing for the accurate and reproducible measurement of more reactive compounds at trace levels to minimize analyte degradation and reduce peak tailing. Building on experience in developing deactivation chemistries for capillary tubing, Agilent has released a novel fused silica for GC and GC/MS applications. This Ultimate Plus deactivation technology elevates surface deactivation to a new level. This technical overview describes the testing of the Agilent Ultimate Plus deactivated tubing and compares it to tubing from another supplier, using two procedures: Chromatographic test for inertness, by measuring peak asymmetry and relative recoveries of several compounds Temperature stability and flexibility test for robustness, by assessing the change in color of the polyimide coating of different tubing observed after 72 or 144 hours of thermal exposure to 360 °C. In addition, the flexibility of tubing before and after temperature stability testing was also investigated, during which the tubing was destroyed by extreme bending.

Agilent Ultimate Plus Fused Silica Tubing · Agilent Ultimate Plus Fused Silica Tubing Technical Overview Introduction Deactivated fused silica tubing is widely used for guard columns,

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Agilent Ultimate Plus FusedSilica Tubing

Technical Overview

Introduction

Deactivated fused silica tubing is widely used for guard columns, transfer lines, orlong retention gaps in GC and GC/MS applications with heavy matrix, and foranalysis of semivolatile compounds [1,2,3,4]. High inertness is a key requirement oftubing for the accurate and reproducible measurement of more reactive compoundsat trace levels to minimize analyte degradation and reduce peak tailing. Building onexperience in developing deactivation chemistries for capillary tubing, Agilent hasreleased a novel fused silica for GC and GC/MS applications. This Ultimate Plusdeactivation technology elevates surface deactivation to a new level. This technicaloverview describes the testing of the Agilent Ultimate Plus deactivated tubing andcompares it to tubing from another supplier, using two procedures:

• Chromatographic test for inertness, by measuring peak asymmetry and relativerecoveries of several compounds

• Temperature stability and flexibility test for robustness, by assessing the changein color of the polyimide coating of different tubing observed after 72 or144 hours of thermal exposure to 360 °C. In addition, the flexibility of tubingbefore and after temperature stability testing was also investigated, duringwhich the tubing was destroyed by extreme bending.

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Material and MethodsTubing inertness was tested using the tandem-column setupshown in Figure 1. The GC reference column was anAgilent J&W VF-5ms, 30 m × 0.25 mm, 0.25 µm (p/n CP8944).A system test was initially performed to establish the baselevel inertness profile, in which a piece of reference columnwas connected to a flame ionization detector (FID) (Figure1A). Subsequently, the Agilent Ultimate Plus or fused silicatubing from another supplier was replaced to connect to theFID detector (Figure 1B). The inertness of the tubing wasevaluated with respect to peak asymmetry and recoveries ofcompounds in two test mixtures (Test Mix 60 and Very InertMix 2) [5,6], shown in Tables 1 and 2. The composition ofcompounds known to adsorb onto active sites of tubing inthese test mixtures (for example, 1-decanol, 4-picoline,trimethyl phosphate, and 1,2-pentanediol) were carefullyselected, which provided an effective evaluation of tubinginertness performance.

Inlet Detector (FID)

Ultimate Union

InletDetector (FID)

Reference column (VF-5 ms)

Reference column (VF-5 ms)

Ultimate Union

10-cm reference columnA

B

Agilent/other supplier tubing

Figure 1. The tandem-column setup of system test (A) andAgilent/other supplier tubing test (B).

Table 1. Test Mix 60 (0.1 mg/mL cyclohexane).

Peak no. Compound Amount on column (ng)

1 1-Octanol 12 n-Undecane 13 2,6-Dimethylphenol 14 2,6-Dimethylaniline 15 n-Dodecane 16 Naphthalene 17 1-Decanol 18 n-Tridecane (used as 100% reference) 19 Decanoic acid ME 1

Table 2. Very Inert Mix in dichloromethane.

Peak no. Compound Amount on column (ng)

1 Methane –2 Propionic acid 13 iso-Butyric acid 14 n-Butyric acid 15 Octene 0.56 Octane 0.57 1-Nitrobutane 18 4-Picoline 29 Trimethyl phosphate 510 1,2-Pentanediol 211 Propylbenzene 112 1-Heptanol 113 3-Octanone 114 n-Decane (used as 100% reference) 1

ConditionsVery Inert Mix 2

Oven: 60 °C for 20 minCarrier: Hydrogen, 1.35 mL/minInjector: 250 °C, split 1:75, 1 µLDetector: FID at 325 °C,

400 mL/min air, 30 mL/min hydrogen, 30 mL/min nitrogen make-up

Test Mix 60

Oven: 120 °C for 20 minCarrier: Hydrogen, 1.35 mL/minInjector: 250 °C, split 1:100, 1 µLDetector: FID at 325 °C,

400 mL/min air, 30 mL/min hydrogen, 30 mL/min nitrogen make-up

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Results and Discussion

Chromatographic testThe trial of Test Mix 60 was performed at an oven temperatureof 120 °C. Figure 2 shows a chromatographic comparison ofthe system test, with Agilent and another supplier tubing (6 m × 0.53 mm). No significant difference in performancewas evident by visual inspection (Figure 2). Peak asymmetry(measured at 10% peak height) and recoveries were used forevaluation of inertness performance between Agilent andother supplier tubing.

6.66.46.265.85.65.45.254.84.64.44.243.83.63.43.232.82.62.42.221.81.61.41.210.8

140

130

120

110

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90

80

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60

50

40

30

20

10

0

2.72

2.91

3.05 3.64

3.84

3.97

4.985.52

6.08

2.70

2.89

3.04 3.633.83

3.96

4.96 5.526.07

1.93

2.12

2.272.86

3.06

3.19

4.18 4.74

5.29

RT (min)

7

2

3

6

89

54

1

pAXOffset: 0YOffset: 38

Peak ID1. 1-Octanol2. n-Undecane3. 2,6-Dimethylphenol4. 2,6-Dimethylaniline5. n-Dodecane6. Naphthalene7. 1-Decanol8. n-Tridecane9. Decanoic acid ME

Figure 2. Comparison of different types of tubing, 6 m × 0.53 mm, using Test Mix 60. Top chromatogram: system test with anAgilent J&W VF-5ms as reference column connected to a 10-cm reference column using an Agilent Ultimate Union(p/n G3182-60581) and UltiMetal Plus Flexible Metal ferrule (p/n G3188-27503). Middle chromatogram: 10-cm reference columnreplaced by 6-m Agilent Ultimate Plus deactivated fused silica tubing. Bottom chromatogram: 10-cm reference column replacedby 6-m deactivated fused silica tubing from another supplier.

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In Figure 3, peak asymmetry values of a nonpolar compound(n-decane) were similar for Agilent and other supplier tubing.These values were close to 1, which is defined as theasymmetry factor of an ideal peak. However, peak asymmetryfactors of a polar compound (1-decanol) using Agilent tubingwere closer to 1 than those of other supplier tubing, in avariety of internal diameters. Differences were moresignificant with larger id tubing. This indicated the improvedinertness performance of Agilent tubing compared to tubingfrom another supplier, explained by interactions between polarcompounds and active sites on the surface of deactivatedfused silica tubing, which results in an increase in peakasymmetry of these compounds. Better relative recoveries of1-decanol (compared to n-tridecane) were also found forAgilent tubing (shown in Figure 4).

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Systemtest

Agilent id0.12 mm

Othersupplier id0.12 mm

Agilent id0.18 mm

Othersupplier id0.18 mm

Agilent id0.53 mm

Othersupplier id0.53 mm

1-decanoln-C13

Figure 3. Asymmetry (measured at 10% peak height) of 1-decanol when using Agilentor other supplier deactivated fused silica tubing, compared to system test. Duplicatetubing was tested.

Systemtest

Agilent id0.12 mm

Othersupplier id0.12 mm

Agilent id0.18 mm

Othersupplier id0.18 mm

Agilent id0.53 mm

Othersupplier id0.53 mm

01020304050

%

60708090

Figure 4. Relative recoveries (compared to n-tridecane) of 1-decanol when usingAgilent or other supplier deactivated fused silica tubing, compared to system test.Duplicate tubing was tested.

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The inertness performance of the Agilent tubing and othersupplier tubing was also tested using a Very Inert Mix 2 at anoven temperature of 60 °C. The separation results of this testmixture indicated that the Agilent tubing clearly showedsignificantly improved inertness compared to tubing fromanother supplier. Trimethyl phosphate, 1,2-pentanediol, andn-propylbenzene (compounds 9-11) were separated whenusing Agilent tubing (middle chromatogram, Figure 5).Conversely, trimethyl phosphate and 1,2-pentanediol werestrongly adsorbed due to active surface of other suppliertubing. As a result, the peaks were small with heavy tailing,which resulted in apparent coelution with n-propylbenzene(bottom chromatogram, Figure 5).

pAXOffset: 0YOffset: 15

1110.5109.598.587.576.565.554.543.532.521.51

60

56

52

48

44

40

36

32

28

24

20

16

12

8

4

2.52 2.95

3.22

3.36

3.47

4.134.72

8.409.09 9.84

2.562.96

3.24

3.43

3.53

4.22 4.74

6.68 7.07

7.49

8.42 9.1810.02

1.561.97

2.23

2.44

2.54

3.20

3.57

5.31

5.79

6.43

7.248.07 8.92

RT (min)

723

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12 13 14

5

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1

72 3

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1213 14

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54

Peak ID1. Methane2. Propionic acid3. iso-Butyric acid4. n-Butyric acid5. Octene6. Octane7. 1-Nitrobutane8. 4-Picoline9. Trimethylphosphate10. 1,2-Pentanediol11. Propylbenzene12. 1-Heptanol13. 3-Octanone14. n-Decane

Figure 5. Comparison of different types of tubing, 6 m × 0.53 mm, using Very Inert Mix 2. Method as for Figure 2.

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Temperature stability and flexibility testMechanical stability is one of the most important parametersof tubing and was assessed using a flexibility test. Severalexamples of Agilent and other supplier tubing were bent tominimum diameters before breakage occurred. Eachmeasurement used 15 cm of tubing. The average value ofminimum bend diameter for 10 measurements per tube wascalculated. Subsequently, the minimum bend radius wasconverted into a force value using our empirical formula,which depends on the internal diameter of tubing (shown inTable 3). The higher the force, the stronger the tubing.Figure 6 shows a comparison of strength between Agilentand other supplier tubing at different internal diameters.There was no significant difference in strength between thenarrow Agilent and other supplier tubing (id 0.12 and0.18 mm). However, Agilent Ultimate Plus tubing showedimproved results compared to tubing from another supplier at0.53 mm id.

To investigate the influence of long-term thermal exposure onthe strength of Agilent tubing, a combined experiment oftemperature stability and flexibility was carried out. Thestrength of several Agilent tubes was measured before andafter thermal exposure of 144 hours at 360 °C (Figure 7). Ingeneral, measurements indicated that there was nosignificant difference in the strength of Agilent tubing beforeand after lifetime testing for all internal diameters, except fortubing of 0.53 mm id. These results were reasonable, becauselarge internal diameter tubing has larger surface areacompared to smaller diameter tubing.

Agilent id0.12 mm

Othersupplier id0.12 mm

Agilent id0.18 mm

Othersupplier id0.18 mm

Agilent id0.53 mm

Othersupplier id0.53 mm

0

100

200

300

400

500

600

700

Forc

e (K

psi)

Figure 6. Strength test of Agilent and other supplier tubing at different internal diameters.

0

100

200

300

400

500

600

700

id 0.12 mm id 0.18 mm id 0.25 mm id 0.32 mm id 0.53 mm

Forc

e (K

psi)

Before After

Figure 7. Strength of Agilent tubing before and after lifetime testing for 144 hoursexposure at 360 °C.

Table 3. Calculation of force value from minimum bend radius

Internal diameter (mm) Formula

< 0.25 y = 1600.1x–1.001

0.32 y = 2123.9x–1.005

0.53 y = 3455x–1.003

where y = force value, x = minimum bend radius

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Another test of temperature stability was performed for 72 hours exposure at 360 °C to compare eight Agilent fusedsilica deactivated tubes (left) and one other supplier fusedsilica deactivated tube (right with red arrow), as shown inFigure 8. The color of the external polyimide coating of all thetubing was the same before thermal exposure (top image).However, the color of the external coating of all Agilenttubing was unchanged after long-term thermal exposure(eighth left tube, bottom image). Conversely, the externalcoating of tubing from another supplier changed to a darkercolor because of damage to the polyimide coating (one righttube, bottom image). This may lead to brittleness, which canshorten the lifetime of the tubing and make it more difficult toachieve a leak-free seal when using press-fit unions.

Table 4. Agilent deactivated fused silica tubing order guide. Avariety of inner diameters and lengths are available.

Part number Description

CP801206 Fused silica, Ultimate Plus Deactivated, 0.12 mm × 6 m

CP801805 Fused silica, Ultimate Plus Deactivated, 0.18 mm × 5 m

CP801806 Fused silica, Ultimate Plus Deactivated, 0.18 mm × 6 m

CP801810 Fused silica, Ultimate Plus Deactivated, 0.18 mm × 10 m

CP802505 Fused silica, Ultimate Plus Deactivated, 0.25 mm × 5 m

CP802510 Fused silica, Ultimate Plus Deactivated, 0.25 mm × 10 m

CP802530 Fused silica, Ultimate Plus Deactivated, 0.25 mm × 30 m

CP803205 Fused silica, Ultimate Plus Deactivated, 0.32 mm × 5 m

CP803210 Fused silica, Ultimate Plus Deactivated, 0.32 mm × 10 m

CP803230 Fused silica, Ultimate Plus Deactivated, 0.32 mm × 30 m

CP805305 Fused silica, Ultimate Plus Deactivated, 0.53 mm × 5 m

CP805306 Fused silica, Ultimate Plus Deactivated, 0.53 mm × 6 m

CP805310 Fused silica, Ultimate Plus Deactivated, 0.53 mm × 10 m

CP805330 Fused silica, Ultimate Plus Deactivated, 0.53 mm × 30 m

CP801505 Fused silica, Ultimate Plus Deactivated, 0.15 mm × 5 m

CP801510 Fused silica, Ultimate Plus Deactivated, 0.15 mm × 10 m

Figure 8. Eight Agilent fused silica tubes (left) and a fused silica tube from another supplier (right) before (top image) and after (bottom image) a temperature stability test at 360 °C over 72 hours.

www.agilent.com/chem

Agilent shall not be liable for errors contained herein or for incidental or consequentialdamages in connection with the furnishing, performance, or use of this material.

Information, descriptions, and specifications in this publication are subject to changewithout notice.

© Agilent Technologies, Inc., 2014Printed in the USASeptember 5, 20145991-5142EN

Conclusions

Agilent Ultimate Plus tubing showed better performanceoverall for inertness, mechanical strength, and thermalstability when compared to deactivated fused silica tubingfrom another supplier. The use of Agilent tubing is, therefore,recommended for any GC or GC/MS application where aguard column, retention gap, or GC restrictor is used. Table 4lists part numbers and product descriptions.

References

1. Anon. DuraGuard Columns: GC Columns with Built-InProtection. Application note, Agilent Technologies, Inc.Publication number 5988-7215EN (2002).

2. Doris Smith, Ken Lynam. Evaluating CLP and EPAMethods for Pesticides in Water Using Agilent J&W DB-CLP1/DB-CLP2 GC columns. Application note, Agilent Technologies, Inc.Publication number 5991-0615EN (2012).

3. James D. McCurry. Automated Standard and SamplePreparation for Multiple Gas Chromatographic Analysesof Biodiesel. Application note, Agilent Technologies, Inc.Publication number 5990-3781EN (2009).

4. Yamin Wang. Analysis of Sulfur Compounds in PetroleumGases and Natural Gas. Application note, AgilentTechnologies, Inc. Publication number 5991-4643EN(2014).

5. J. Luong, R. Gras, W. Jennings. J. Sep. Sci. 30, 2480(2007).

6. Anon. Agilent J&W Ultra Inert GC Columns: A New Toolto Battle Challenging Active Analytes. Technicaloverview, Agilent Technologies, Inc. Publication number5989-8665EN (2008).