Fresenius Z. Anal. Chem. 305, 1 9 3 - 195 (1981) Fresenius Zeitschrift fiJr

Gas-Chromatographic Quantitation of Lindane in Household Insecticide Spray Cans

Adam Vincze*, Leon Gefen, Abraham Fisher, Adam Shatkay, and Ruth Saranga

Israel Inst. for Biological Research, Ness-Ziona, Israel

~) Springer-Verlag 1981

Gas-chromatographische Bestimmung von Lindan in Haushalts-Spraydosen

Zusammenfassung. Das Treibmittel wird durch Aus- frieren abgetrennt und die Insecticidl6sung gas-chro- matographisch mit Electron-capture Detektor analy- siert. Das reine cMsomere dient als innerer Standard. Der Fehler betrfigt _+ 5 %.

Summary. A method was developed for the determi- nation of the lindane content of commercial household insecticide spray aerosols. After the propellant is re- moved from the chilled contents of the spray packages the hydrocarbon solution is analysed for its lindane content by electron-capture gas chromatography. Pure e-isomer of hexachlorocyclohexane serves as the in- ternal standard. Experimental error is +_ 5 %.

Key words: Best. von Lindan, 7-Hexachlorcydohexan in Spraydosen; Chromatographie, Gas; Electron cap- ture

Lindane is the ?-isomer of hexachlorocyclohexane (HCCH), sometimes erroneously referred to in agricul- tural and entomological literature as benzylhexachlo- ride (BHC). This is one of the nine possible confor- mers but actually one out of four present in crude synthetic lindane [2]. In the y-conformer there are 3 adjacent axial chlorine atoms.

el

CI

CI

CI

The structure determines the physical characteristics and of course the biological activity. Indeed, there are

* Address for correspondence

physicochemical differences that enable one to dis- tinguish among isomers. Electron-impact mass spec- trometry can be used to distinguish between isomers, the analysis relying mainly on difference in abundance ratios of the m/z 288 to m/z 181 primary ions [6, 7].

For quantitative purposes various methods are used, such as UV spectroscopy [3] and gas chromatog- raphy [L 5]. We describe in the present communication a gas-chromatographic method with electron-capture detection for the special case of estimating the quantity of lindane in pressurized household insecticide spray cans 1. Analysing spray-cans poses a special problem; the container must be sampled for analysis in such a way that there is no change in the concentration of the agent to be analysed. The solvent is usually hy- drocarbon while the propellant a freon. Electron- capture detection is most suitable for the purpose of selectively detecting a halogen-containing solute in a non-electron capturing solvent. For the same reason it is important to ascertain removal of all traces of fluorocarbon propellant. Another shortcoming of the electron-capture detector is its non-linear response. However, since our purpose was to validate the con- centration claimed by manufacturers, the method de- veloped could be limited to a short range of con- centrations. We felt that use of another HCCH isomer as the internal standard would be very convenient. Taking equal concentrations, peaks of similar size can be expected. ~-HCCH was chosen and this expectation was borne out. A calibration curve relating the ratio of areas (Ra) as a function of the ratio of weights (Rq) over the range of 1 : 1 to 1 : 8 ng (7 to e isomers) was obtained (Fig. 1). This curve was then used to analyse unknowns.

Materials and Equipment

n-Hexane, the solvent, was obtained from Merck-Darmstadt and was of analytical grade. Lindane was purchased from Supelco and c~- HCCH was a gift from Dr. N. Aronson 's Lab. at the Volcani

1 Lindane is still used in household insecticide formulations in Israel

0016-1152/81/0305/0193/$01.00

I [ I I I I I 1 T

J ~ o

0 f ~

3

2 Ra

, /

0 i 0 I

l 1 I I [ I L I

2 3 4 5 6 7 8 9 Rq

Fig. 1. Calibration curve

Fig. 2. Gas chromatogram of c~- and 7-HCCH

Institute, Belt Dagan, Israel. A Packard model 804 gas chromato- graph equipped with tritium foil electron-capture detector was used in conjunction with an Infotronics model CRS-100 integrator. The column was 4 % OV 17 on Gas Chrom Q 80/100,1/5" x 6 / in silanized glass. A Varian MAT model 112 mass spectrometer was used to verify the identity of the isomers.

Methods

First, we ascertained by comparing the mass spectra of the unknowns with those of the standards that the isomer contained in the samples subjected for analysis was indeed the ? one. The GC conditions yielding base-line separation of ~- and 7-HCCH were estab- lished (see Fig. 2). These were: carrier flow (N2) 50m 1/rain operating temperatures: injection port 220~ Column 195~ isothermal, detector oven 200 ~ C. All were brought to the working temperatures hours before the injections and were kept warm and stable throughout. Retention times of ~- and ~-HCCH were 182" and 230", respectively.

The optimal concentration was found to be several ppm for both isomers when 1 or 2 gl are injected (that is several nanograms total amount per injection). With higher concentrations the detector's sensitivity was found to fall off considerably. Stock solutions: a) lindane I mg/ml hexane; b) ~-HCCH 1 gg/ml hexane. Working solutions : from 2 - 16 ~tl of (a) were added to 2ml of (b) giving solutions containing l - 8 n g of lindane and 1 ng of ~-HCCH per gl of hexane. (The dilution error is 8 in 1008, thus less than 1%).

Injection was on column and 2 gl were injected of each solution. The values obtained are presented in Table i as averages of 4 injections.

The curve, Fig. 1, was prepared from these experi- mental points and seems to be a geometrical one that can be described by Eq. (1) [8].

R, = a Rq b (1)

194 Fresenius Z. Anal. Chem., Band 305 (1981)

Table 1

R~ Rq

1 1 . 2 8 2 1.64 3 1.79 4 2.15 5 2.40 6 2.53 8 2.71

where: R. is the ratio of a r e a s , Rq ratio of quantities and a and b were obtained by computer-minimization of S. S is defined by Eq. (2).

S = / S i ( R . . . . lc -- R . . . . per) 2 (2)

x/ n

where Ra, expCr is the experimental value that fits Rq in experiment i and R .. . . lc is computed by Eq. (1).

Computation yields the following values: a = 1.26, b = 0,38 and S = 0.066. It follows that when R, is within the range 1 to 3 the experimental error is less than 5 %.

Test Analyses. Three commercial insecticide spray cans x, y and z with the given conc. of 0.2 %, 0.2 % and 0.5 %, respectively, were analysed. The cans were chilled to - 25 ~ C in a deep freezer. At this temperature the pressure of the propellant drops sufficiently low and the contents can be removed without loss by spray especially when inverted. 2 - 3 m l were transferred into a concentration vessel described by Junk [4] which serves to concentrate solutions without applying vacuum. The solution was allowed to warm-up to ambient tem- perature in about 15 rain, by which time the propellant boiled off and evaporated. At this stage the solution was transferred into a screw- capped vial.

A. Vincze et al. : Gas-Chromatographic Quantitation of Lindane 195

Since the concentration claimed is 3 orders of magnitude higher than the optimum of the curve, the contents were diluted a thousandfold in n-hexane. For the determination 2 gl of the diluted solution were added to 2ml of standard c~-HCCH solution as described above. The concentration was calculated in the usual way. All concentrations were found to be as claimed.

References

l. De Vos, R. H., Bosma, M. P. M. M., Brouwer, A. E.: J. Chromatogr. 93, 91 (1974)

2. Fieser, L., Fieser, M. : Advanced organic chemistry, p. 786. New York: Rheinhold 1961

3. Horwitz, W. (edit.): Official methods of analysis of the AOAC, p. 534 (1975)

4. Junk, G. A.: J. Chromatogr. 99, 145 (1974) 5. Palmer, L., Kalmodin-Hedman, B. : J. Chromatogr. 74, 21 (1972) 6. Safe, S., Hutzinger, O.: Organic Mass Spec. 1, 217 (1973) 7. Safe, S., Hutzinger, O. (edit.): Mass spec. of pesticides and

pollutants, pp. 131-133. C.R.C. Press (1973) 8. Shatkay, A.: Anal. Chem. 50, 1423 (1978)

Received June 10, 1980