Analyst, January, 1968, Vol. 93, p$. 3941 39 Determination of Aldrin Residues in Vegetables by the Chemical Conversion of Aldrin to Dieldrin BY KOIDU NOREN (Department of Food Hygiene, National Institute of Public Health, Stockholm, Swedm) The determination of aldrin in certain samples of vegetables by gas chromatography has proved to be difficult, as peaks from impurities interfere. To eliminate this disadvantage a method was developed in which aldrin was converted to dieldrin and the amount of dieldrin determined by gas chro- matography. VARIOUS clean-up procedures have been described for use in the determination of chlorinated pesticide residues in plant material by gas chr~matography.~ ,293949596 In this laboratory, the method generally used is based on the procedure of Mills.g In some determinations, however, this method failed to eliminate an impurity that interfered with the gas-chromatographic determination of aldrin. This impurity has also been noted by Goodwin, Goulden and Reynolds,f and by Burke and Guiffrida' using their method for extraction and clean-up.To overcome this problem, Goodwin, Goulden and Reynolds compared gas - liquid chromato- graphy on non-polar and polar stationary phase. Also, separation by liquid - solid chrom- atography (hexane - aluminium oxide) was carried out successfully. Hamence, Hall and Caverly3 treated the sample with chlorine, converting the aldrin into a derivative that could easily be separated from the impurity by gas chromatography. The derivative had about the same retention time as of-DDT, which made it unfit for quantitative determinations in the presence of 09'-DDT. For the purpose of evolving a quantitative method in which most of the common chlorinated pesticides could be separated and determined on the same column by gas - liquid chromatography and electron-capture detection, a procedure has been developed by which aldrin is converted to dieldrin without affecting other chlorinated pesti- cides present.The conversion has also been confirmed by thin-layer chromatography. METHOD Homogenise 1 kg of vegetable, then extract 100.0 g of the homogenised material with 90ml of hexane plus 50 ml of isopropyl alcohol and repeat the extraction with 90ml of hexane plus 20 ml of isopropyl alcohol. Shake the combined extracts with 600 ml of water to remove isopropyl alcohol.Transfer the hexane layer quantitatively to a 200-ml gradu- ated flask and make up to the mark with hexane. Evaporate 50*00ml of the extract, which corresponds to 25.0 g of sample, at reduced pressure at 35" C to 1 to 2 ml, and transfer to a pre-wetted chromatographic column, of 2-cm diameter, containing 15g of Florisil and a 4-cm high layer of anhydrous sodium sulphate. (Before use activate the Florisil for 24 hours at 600" C ; after cooling add 2 per cent. of water and mix carefully.) Elute the pesticides with 150 ml of light petroleum (boiling range 35" to 60" C) - diethyl ether (80 + 20). Evaporate the eluate at reduced pressure at 35" C to 15 ml, transfer the residue quantitatively to a 25-ml graduated flask and make up to the mark with the solvent. Analyse by gas chromatography.This method has been used for lindane, aldrin, chlordane, dieldrin, up'-DDT andpp'-DDT. If the chromatogram indicates the presence of aldrin in the sample, a simple procedure is carried out in which the aldrin is oxidised by peroxyacetic acid at 65" C to the 6,7-epoxy derivative (dieldrin). The reaction mixture is washed with sodium hydrogen sulphite solution to remove the oxidising agent and then with sodium carbonate solution to remove the acid.8 0 SAC and the author. The dieldrin formed in this way is analysed by gas chromatography.40 APPARATUS- KOIDU N O R ~ N : DETERMINATION OF ALDRIN RESIDUES IN [Analyst, Vol. 93 CONVERSION OF ALDRIN TO DIELDRIN Separating funnel-125-ml capacity. Graduated $asks-25 and 100-ml capacity.Water-bath, 65" C. Magnetic stirrer-This is equipped with polyethylene-covered stirring bar. Evaporator. Gas chromatograph-Wilkens Aerograph HyFi 600, equipped with an electron-capture detector, was used. Column-Pyrex glass, Q inch x 5 feet, packed with 5 per cent. DC-11 on Chromosorb W silicone grease, 60 to 80 mesh. Temperature of column-195" C. Temperature of injectio~-210" C. Temperature of detector-195' C. Recorder-Texas instrument, model PWS-IMVG-05-A 25-BT. The gas flow-rate was 75 ml of nitrogen per minute. Benzene, redistilled. Hydrogen peroxide, 30 per cent. w/v, analytical-reagent grade. Glacial acetic acid, analytical-reagent grade. SuZphuric acid, analytical-reagent grade. Sodium hydrogen sul$hite solution, 10 per cent. wlv, aqueous.Sodium carbonate solution-Prepare a saturated aqueous solution. Anhydrous sodium swtphate-Heat overnight at 450" C. PROCEDURE- Gently evaporate 25.00 ml of the cleaned extract, corresponding to 25-0 g of sample, to 0.5 to 1 ml, at reduced pressure at 35" C. A rotating evaporator connected to a water pump was used. Transfer the residue to a 100-ml graduated flask with 25ml of benzene. Add 2-0 ml of hydrogen peroxide, 1.0 ml of glacial acetic acid and 1.0 ml of sulphuric acid. Place the flask in a water-bath at 65" C. Equip the flask with a magnetic stirrer. Stopper the flask and allow to react for 3 hours, with stirring. Then transfer the mixture to a 125-ml separating funnel. Rinse the flask with small portions of benzene and collect the benzene in the separating funnel.Wash the benzene layer by shaking with 25 ml of sodium hydrogen sulphite solution. Allow to separate, and discard the aqueous layer. Repeat the washing with 25 ml of saturated sodium carbonate solution and with 25 ml of water until neutral. The benzene layer is passed through a chromatographic column, of 2-cm diameter, containing 2.5 cm of anhydrous sodium sulphate. Rinse the separating funnel with small portions of benzene and transfer to the column. Elute the column with an additional 10 to 15ml of benzene. Evaporate the collected benzene to 15 to 20 ml at reduced pressure at 35" C. Transfer the benzene extract quantitatively to a 25-ml graduated flask and make up to the mark with benzene. Examine this solution by gas chromatography. TABLE I REAGENTS- RECOVERY OF DIELDRIN FROM ALDRIN ADDED TO THE SAMPLE BEFORE THE EXTRACTION OF THE MATERIAL WITH HEXANE - ISOPROPYL ALCOHOL AND SUBJECTION TO THE PROCEDURE FOR CLEAN-UP WITH FLORISIL AND CONVERSION OF ALDRIN TO DIELDRIN Dieldrin Recovery, Aldrin added, Theoretical, Found, Sample p.p.rn.p.p.m. p.p.m. per cent. Y Carrots .. .. . . 0.050 0-052 0.044 85 0.010 O.OIO4 0.009 1 88 0.010 0-0104 0-0086 83 Potatoes .. . . 0*030 0.052 0.044 85 0-050 0-052 0.046 88 0.050 0.052 0.041 79 0.010 0.0104 0.0081 78 Meanvalue .. .. 84 Cabbage .. . - o*ofjo 0.052 0.043 83January, 19681 VEGETABLES BY THE CHEMICAL CONVERSION OF ALDRIN TO DIELDRIN 41 TABLE I1 RECOVERY OF DIELDRIN FROM THE CONVERSION OF ALDRIN TO DIELDRIN The concentrations are given before and after the conversion procedure Before conversion Aldnn, r-n, Sample p.p.rn. p.p.m.Cabbage .. . . 0~0090 0 0-050 0 0.050 0 0-056 0 0.062 0.011 Potatoes . . . . 0.042 0 0.046 0.021 0.046 0 Carrots . . . . 0*0090 0.01 1 After conversion Dieldrin, theoretically from -7 Found, From aldrin, aldrin, p.p.m. p.p.m. p.p.m. 0.0086 0.0086 0.0094 0.051 0.05 1 0.052 0~0200 0.0090 0.0094 0.047 0.047 0.052 0.055 0.055 0-057 0.079 0-068 0.065 0-044 0.044 0.044 0-062 0-04 1 0.047 0.046 0.046 0.048 Dieldrin Mean value . . Recovery, per cent. 91 98 96 90 96 105 100 87 96 . 95 RESULTS The method has been applied to samples of carrots, cabbage and potatoes. Recovery experiments have been carried out with addition of standard solutions of aldrin to the material before the first extraction of the plant material, and before the conversion procedure.Average recovery of dieldrin from the over-all procedure was 84 per cent. (Table I). In the conversion of aldrin to dieldrin 95 per cent. of the theoretical amount of dieldrin was recovered (see Table 11). Other chlorinated pesticides that may be present in the sample, e.g., lindane, heptachlor, chlordane, o$'-DDT and $$'-DDT, were not affected by this procedure and were recovered to 88 to 101 per cent. from samples of carrots (see Table 111). The sample solution is suitable for further analysis, e.g., by thin-layer chromatography. TABLE I11 RECOVERIES OF SOME CHLORINATED PESTICIDES ADDED TO SAMPLES OF CARROTS BEFORE TO THE PROCEDURE FOR CLEAN-UP WITH FLORISIL AND CONVERSION OF ALDRIN TO DIELDRIN THE EXTRACTION OF THE MATERIAL WITH HEXANE - ISOPROPYL ALCOHOL AND SUBJECTION Pesticide Added, p.p.m. Recovery, per cent. Lindane .. .. .. 0-050 91 Heptachlor . . .. .. 0.050 101, 98 Chlordane . . .. .. 0.050 88, 94 op'-DDT .. .. .. 0.10 91, 98 PP'-DDT .. .. .. 0.50 89, 94 REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. Goodwin, E. S., Gulden, R., and Reynolds, J. G., Analyst, 1961, 86, 697. McKinley, W. P., c O 5 , D. E., and McCully, K. A., J. Ass. OJf. Agric. Chem., 1964, 47, 863. Hamence, J. H., Hall, P. S., and Caverly, D. J., Analyst, 1965, 90, 649. Jones, L. R., and Riddick, J. A., Analyt. Chem., 1952, 24, 669. Mills, Paul A., Onley, J. H., and Gaither, R. A., J. Ass. Ofl. Agrzc. Chem., 1963, 46, 186. Mills, Paul A., Ibid., 1959, 42, 734. Burke, J., and Giuffrida. L.. Ibid., 1964, 47, 326. McKinney, R. M., and Pearce, G. W., J. Agric. Fd Chem., 1960, 8, 456. Received March 281h, 1967