Gas-chromatographic analysis of insensitive pesticides as their

sample sizes often in the presence of carrier gases which would not normally be used (CHI, C2H6, CO, '202, etc.) it might be worthwhile in the future ...
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sample sizes often in the presence of carrier gases which would not normally be used (CHI, C2H6, CO, ' 2 0 2 , etc.) it might be worthwhile in the future to use radioactively labelled cornpounds as samples. Extremely small samples could then be detected so that infinite dilution would be very closely approached, and the nature of the carrier gas would be immaterial, thus widening the scope of gas mixtures for which interaction second virial coefficients can be obtained.


We thank Don Carle for making available to us the Carle Instruments' rotary valve used for injection, and to Brian W. Gainey for helpful suggestions. RECEIVED for review March 20, 1968. Accepted April 30, 1968. Based on a paper presented at the 155th National Meeting, ACS, San Francisco, Calif., April 1968.

Gas Chromatographic Analysis of Insensitive Pesticides as Their HalomethyldimethyI siIyI Derivatives C. A. Bache, L. E. St. John, Jr., and D. J. Lisk Pesticide Residue Laboratory, Cornell Unicersity, Ithaca, N . Y. 14850

The bromo- and chloromethyldimethylsilyl derivatives of acidic and phenolic pesticide and herbicide compounds have been prepared which greatly enhance their responsewhen subsequently analyzed by electron affinity and emission spectrometric gas chromatography. The method is rapid and versatile permitting detection of these compounds in the range of 1 to 100 nanograms. The procedure has been applied to analysis of soil.

GASCHROMATOGRAPHIC ANALYSIS of pesticides using halogensensitive detectors is often limited by the absence or lack of sufficient halogens in the molecule to provide adequate response. Bromination of aromatic amine ( I ) and phenolic (2) agricultural chemicals has been successfully applied to greatly enhance their response to electron affinity detection. Other reactions have been used such as the Zeisel alkoxy1 reaction with organophosphorus insecticides to produce alkyl iodides (3),chloroacetylation of phenols (4) and amines (3,haloacetylation of sterols trifluoroacetylation of amines ( 5 ) and amino acids (3, and pentafluoropropionylation and heptafluorobutyrlation of various amines (5). Fishbein and Zielinski (8) prepared trimethylsilyl derivatives of pesticidal carbamates and ureas prior to gas chrornatographic analysis. Steroids have been chromatographed as their bromo- (9) and chloro- (IO, 11) methyldimethylsilyl ether derivatives. In the work reported, the feasibility of preparing and chromatographing the bromo- and chloromethyldimethylsilyl derivatives of halogen deficient pesticide com-


(1) W. H. Gutenmann and D. J. Lisk, J. Agr. Food Chem., 11, 468 (1963). (2) Ibid., 13, 48 (1965). (3) Ibid., 11, 470 (1963). (4) R. J. Argauer, ANAL.CHEM., 40, 122 (1968). (5) _ . . , D. D. Clarke. S . Wilk. and S. E. Gitlow. J . Gas Chromaton.. 310 (1966). (6) R. A. Landowne and S. R. Lipsky, ANAL.CHEM., 35, 532 (1963). ( 7 ) M. Stefanovic and B. L. Walker, ibid., 39, 710 (1967). (8) L. Fishbein and W. L. Zielinski, Jr., J . Chromatog., 20, 9 (1965). (9) C. Eaborn, D. R. M. Walton, and B. S. Thomas, Chem. Ind. (London), 1967, p 827. (10) W. J. A. VandenHeuvel, J. Chromatog., 27, 85 (1967). (11) B. S . Thomas, C. Eaborn, and D. R. M. Walton, Chem. Commun., 2, 408 (1966).

pounds and certain of their metabolites in various chemical classes has been studied. EXPERIMENTAL

Reagents. The bromo- and chloro-methyldimethylchlorosilanes were purchased from Pierce Chemical Co., Rockford, Ill., and were kept refrigerated. The diethylamine was Eastman White Label grade and was redistilled and stored in the dark over anhydrous sodium sulfate. N-hexane was shaken with concentrated sulfuric acid and washed with distilled water. It was then redistilled over potassium hydroxide pellets and stored over anhydrous sodium sulfate, Procedure. The derivatives were formed by an adaptation of the procedure of Eaborn et al. (9) as follows: One milliliter of hexane, 0.075 ml of diethylamine, and 0.09 ml of bromo- or chloromethyldimethylchlorosilane were added to a 5-ml glass vial which was stoppered and shaken vigorously. The mixture was centrifuged at 1500 rpm for 15 minutes. A 0.4-ml portion of the supernate was transferred to an 8-ml glass-stoppered test tube containing 0.1 ml of ethyl acetate in which was dissolved up to 100 micrograms of the pesticide or metabolite to be reacted. A 10/30 standard-taper male ground joint (with the full 15-cm length of glass tubing attached) was placed in the top (as an air condenser) and the contents were refluxed at 65 "C for 30 minutes. The contents were immediately cooled and the condenser was rinsed with 0.5 ml of hexane. The solution was appropriately diluted with hexane and chrornatographed. If the tubes were stoppered and the contents kept dry, the derivatives were stable for several hours. Two chromatographs and detection systems were employed. The derivatives were examined using an electron affinity detector. This system comprised a Barber-Colman Model 10 gas chromatograph with a battery operated BarberColman Model No. A-4071, 6-cc detector containing 56 pc of radium-226. The detector was operated at 2 volts and the relative electrometer gain was 10,000. The recorder was a Wheelco, 0 to 50 mV equipped with 10-inch chart paper, running 10 inches per hour. The column was borosilicate glass, U-shaped, 5-mm i d . , and 2 feet long. The packing was 10% DC-200 on 100- to 120-mesh Gas-Chrom Q. Connections between the column and detector were made with Teflon tubing and nitrogen (60 cc per minute) was the carrier gas. The isothermal column temperatures used for the various compounds studied ranged from 110 to 200 "C. Response was also measured using a microwave-powered, low pressure, helium plasma emission detector (11) and VOL 40,

NO. 8, JULY 1968


Table I. Chromatographic Data for Halomethyldimethylsilyl Derivatives of Various Agricultural Chemicals and Metabolites

Compound ACIDS N-1-naphthylphthalamic acid (Alanap) Dimethylaminosuccinamic acid (Alar) 2-Methyl-4-chlorophenoxyacetic acid (MCPA) Naphthalene acetic acid (NAA) 2,4-dichlorophenoxyacetic acid (2,4-D) Neo-decanoic acid (NDA) PHENOLIC COMPOUNDS CChlorocatechol (metabolite of 2,4-D) 2-Methyl-4 chlorophenol (metabolite of MCPA) 2,CDichlorophenol(metabolite of 2,CD) I-Naphthol (metabolite of Carbaryl)’ 3,5-Dimethyl-4-thiomethyl phenol (metabolite of Mesurol)2 3,5-Dimethyl-4-dimethylaminophenol(metabolite of Zectran)a b

Chloromethyldimethylsilyl derivative. Bromomethyldimethylsilyl derivative.




Relative retention time Cla Brb

Sensitivity, nanograms Electron capture Microwave emission c1 Br c1 Br

23.95 13.74 2.69 3.85 3.65 0.46

29.58 24.74 3.89 5.58 5.35 0.53

3.66 0.49 0.60 1.39

6.48 0.72 0.87 2.04

4.5 10


1.5 25





15 100 30

40 36 15 1.8



159 64 99 91 276

111 67 61 143 202

0.8 0.9

21 40 35 71

19 46 17 38









2.2 15



12 1

* 3,5-Dimethyl-4-thiomethylphenyl-N-methylcarbamate. * 3,5-Dimethyl-4-dimethylaminophenyl-N-methylcarbamate. monitoring the a!omic bromine (4785.5 A) and atomic chlorine (4794.5 A) emission. The operating parameters for this system have been described (12). The column was identical to that used with the electron affinity detector except that the i.d. was 3 mm. RESULTS AND DISCUSSION Table I lists the compounds for which derivatives were successfully prepared, their sensitivities using both detection modes, and their retention times. Sensitivities correspond to the amount (nanograms) of the compound which was injected to produce a half scale deflection (a peak about 12 cm high). NDA was the only compound that showed multiple (two) chromatographic peaks of comparable size following derivatization. (Using flame ionization detection, up to 5 peaks are resolved representing its isomers). All of the retention times in the table are relative to that of lindane (hexachlorocyclohexane-gamma isomer). The retention time of lindane at 120 and 184 O C was 11.1 and 0.9 minute, respectively. Only acids and phenolic compounds were able to be derivatized. Efforts to prepare these derivatives of 3amino-l,2,4-triazole (amitrole), various intact carbamates [carbaryl, Mesurol, Zectran, isopropyl N-(3-chlorophenyl) carbamate (CIPC)], or substituted ureas [3pchlorophenyl1,l-dimethylurea (monuron), 3 43,4-dichlorophenyl)-l , l -dimethylurea (diuron)] were unsuccessful. Nor could 2,4dinitro-o-cresol be derivatized. Figure 1 illustrates standard curves of the chloromethyldimethylsilyl ether of 1-naphthol and the corresponding silyl ester of naphthalene acetic acid using the microwave-powered emission detector. Five 100-nanogram portions of this 1naphthol derivative were prepared and chromatographed. The mean peak height was 17.02 += 0.59 cm at the 9575 confidence level based on a standard deviation (13) of 0.476. The method was applied to the analysis of 2-methyl-4chlorophenoxyacetic acid (MCPA) in soil. The procedure

(12) C. A. Bache and D. J. Lisk, ANAL.CHEM.,39,786 (1967). (13) W. J. Youden, “Statistical Methods for Chemists,” 2nd ed., Wiley, New York, 1951. 1242


NANOGRAMS INJECTED Figure 1. Standard curves of chloromethyldimethylsilyl ether of 1-naphthol (0-0) and chloromethyldimethylsilyl ester of naphthalene acetic acid (A-A) Microwave powered emission detector involved extraction of 25 grams of soil (Bath gravelly silt loam) with 100 ml of acetone and 1 ml of 5N hydrochloric acid by shaking mechanically for 1 hour. The slurry was filtered into a 100-ml volumetric flask and rinsed to volume with acetone. A 4-ml aliquot of the filtrate was transferred to an 8-ml glass-stoppered test tube and evaporated with air. Three milliliters of anhydrous diethyl ether were added and again evaporated to dryness. Following addition of 0.1 ml of ethyl acetate to the tube, 0.4 ml of either (bromo or chloro) silyl reagent was added and the remainder of the procedure was conducted as described. The recovery of 2 to 20 ppm of MCPA added to soil with chromatographic analysis of the compound as either the bromo or chloro silyl ester and using both detection modes ranged from 87 to 120 %. Appropriate isolation procedures are now being investigated to enable analysis of the compounds studied in other biological samples. RECEIVED for review March 28, 1968. Accepted April 12, 1968.