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Analytical Methodology for Bioactive Compounds Photochemically Assisted Analysis of Chlorinated Hydrocarbon Pesticides in the Presence of Polychlorinated Biphenyls Richard A. Leavitt, George C. C. Su, and Matthew J. Zabik Pesticide Research Center, Michigan State University, East Lansing, Mich. 48823
One of the major problems posed by the widespread presence of polychlorinated biphenyls (PCB’s) in the environment, aside from ecological considerations, is that they interfere with gas-liquid chromatographic (GLC) analysis for the chlorinated hydrocarbon pesticides ( I , 2 ) . Attempts to separate and quantify chlorinated pesticides in the presence of PCB’s have been largely unsuccessful. Existing methods of separation are either inefficient or subject to problems of reproducibility (3-5). The continuing need to determine pesticide concentrations in the presence of PCB’s has prompted us to examine the feasibility of removing the interfering PCB’s by photochemical degradation prior to analysis. Photochemical studies at 280-320 nm indicate that PCB’s with three or more chlorines will degrade stepwise to mono- and dichlorobiphenyls (6-8). These PCB’s under GLC conditions normally employed have short retention times and do not interfere with the analysis of most chlorinated pesticides. The chlorinated pesticides are of course not immune to photodegradation and form a variety of products depending upon conditions (9).This, however, can be quite helpful in identification, as well as quantification. of certain pesticides as recently described by Glotfelty (10) and Bills et al. ( 1 1 ) . Bills (12) has also reported that mixtures of chlorinated pesticides can be identified in the presence of PCB’s by trapping the GLC effluents, subjecting them to W irradiation, and rechromatographing them t o observe any interferences or changes which occur when both are present. It was the intent of this study to develop analytical methodology to enable quantitative analysis of both PCB’s and the chlorinated pesticides in the presence of each other. L. M . Reynolds. Bu//. Environ. Contam. Toxicol.. 4 , 128 (1969) L. M . Reynolds, Residue Rev., 34, 27 (1971) and references therein. M. L. Porter and J. A. Burke, J . Ass. Offic. Anal. Chem.. 5 4 , 1426 (1971). J. A. Armor and J. A . Burke, J. Ass. Offic. Ana/. Chem., 54, 175 (1971). J. A. Armor and J. A. Burke, J. A S S . Offic. Ana/. Chem., 53, 761 (1970). 0. Hutzinger. S. Safe, and V . Zitko, Environ. Heaith Perspectives, 15 (1972). S. Safe and 0. Hutzinger, Nature (London). 232, 641 (1971). L. 0. Ruzo. M. J. Zabik and R. D. Schuetz, Bu//. Environ. Contam. roxicoi., 8, 217 (1972) K . A . Banks and D. D. Bills, J. Chromotogr., 33,450 (1968) D. E. Glotfelty, Ana/. Chem.. 44, 1250 (1972) W . M. Kaufman. D. D. Bills, and E. J. Hannon, J. Agr. Food Chem., 20, 628 (1972). E. J. Hannan. D. D. Bills, and J. L. Herring, J. Agr. food Chem., 2 1 , 87 (1973).
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EXPERIMENTAL A p p a r a t u s . GLC analyses were performed on a Beckman GC-4 chromatograph equipped with a Beckman discharge electron capture detector using high purity helium as both discharge and carrier gas. T h e column was a 3-ft X ?&-in.0.d. stainless steel tube containing 270 Apiezon L and 2% SE-30 on 60-80 mesh GasChrom Q. On-column injection was utilized with the column oven maintained isothermally a t 200 “C. The detector and sample inlet compartments were held at 250 “C. Samples were irradiated in a Rayonet type RPR-208 photochemical reactor equipped with RLL-3000A Lamps (280-340 n m emission). a rotating multi-sample holder, and a cooling fan to approximately maintain room temperature. Photoproducts were identified by comparison with authentic samples and by mass spectrometry using a DuPont Model 21-490 spectrometer interfaced via a jet separator with a Beckman GC-65 gas chromatograph. Materials. Aroclor 1254 was generously furnished by the Monsanto Chemical Corporation and used as received. p,p’-DDT and p,p’-DDE were used as received from Aldrich Chemical Corporation. Dieldrin (99+%) from Shell Chemical Company was used without further purification. Hexane was fractionally distilled in an all-glass system and the center fraction retained for use. Various test standards were prepared from these materials with concentration ranges of 0.1-50 p p m . Procedures. Samples were first injected into the gas chromatograph to analyze for Aroclor 1254 by measuring the total peak area of P C B peaks not interfered with by the pesticide peaks. Comparison with calibrated Aroclor 1264 standards gave the amount of Aroclor 1254 present. Samples, as well as individual calibrated pesticide standards (two or three per pesticide in the concentration range expected), were then saturated with oxygen and irradiated for a period of 16 hours in Teflon (DuPont) capped Pyrex (Corning Glass Works) test tubes under photolytic conditions described above. Quantitation of the chlorinated pesticides was based on the amount of pesticide remaining after photolysis or on the amount of photoproduct formed.
RESULTS AND DISCUSSION Three chlorinated pesticides, dieldrin, DDT, and DDE were chosen to test the applicability of removing PCB’s by photochemical degradation. Under our GLC conditions, certain PCB peaks interfered with each pesticide peak. In addition, the GLC peaks for DDE and dieldrin had similar retention times. To determine the optimum period of irradiation a t 280-320 nm (Irradiation at 253.7 nm was quite destructive to the pesticides and caused large trailing solvent peaks probably due to chlorination of the solvent.), two concentrations (1 and 10 ppm) of Aroclor 1254 were photolyzed and the total GLC peak area was measured as a function of time. In addition to the reduction in total PCB peak area, there was, as one would expect, a general shift to peaks of shorter retention times as the PCB’s were stepwise photochemically degraded to the less chlorinated iso-
ANALYTICAL CHEMISTRY, VOL. 45, NO. 12, OCTOBER 1973
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Figure 1. Gas c h r o m a t o g r a m of 1 0 ppm of A r o c l o r 1 2 5 4 b e f o r e (6)
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Figure 2. Gas c h r o m a t o g r a m o f 1 0 p p m A r o c l o r 1 2 5 4 , 4 ppm D D E , 4 pprn D D T , and 0 5 ppm D i e l d r i n b e f o r e (B) and after ( A ) photolysis
mers. The two concentrations of Aroclor 1254 had similar rates of photodegradation and after 16 hours very little further degradation occurred leaving a residual of peaks having relatively short retention times. The total peak area of the photolyzed 10 ppm PCB was, for example, reduced to 10% that of the unphotolyzed as shown in Figure 1. Under our photolytic conditions, the chlorinated pesticides also underwent varying degrees of degradation as shown in Figure 2. The parent peaks of DDT and dieldrin were reduced to 72 and 9070, respectively, of their starting concentrations (Photolysis of standards eliminates any starting material concentration sensitivity of these numbers). DDE was totally photodecomposed after two hours of irradiation. Of the resultant three major photoproducts, p , p ’ -dichlorobenzophenone, 2,2-bis-( p-chlorophenyl)- 1chloroethylene, and 2-(p-chlorophenyl)-2-(dichlorophenyl)1-chloroethylene, the one with the shortest retention time, p,p’-dichlorobenzophenone, was best suited for analysis since it did not interfere with the other pesticide peaks and was quite stable to further photodegradation. However, it should be noted that the formation of this photodegradation product is quite sensitive to the relative oxygen content of the solution. For example, the photolysis of 1 ppm and 50 ppm DDE in hexane gave quite different photoproduct ratios unless the solutions were first either degassed or saturated with oxygen. The latter process is preferable since it maximizes the benzophenone product. However, even four freeze-thaw cycles a t 0.01 Torr do not completely remove the dissolved oxygen which allows the benzophenone product to form. The presence of oxygen apparently does not significantly inhibit the photodegradation of PCB’s a t the 1-10 ppm level. T o test the reproducibility of the method, a residue sample was prepared containing known concentrations of Aroclor 1254, DDE, dieldrin, and DDT. The results of this test quantification are given in Table I.
APPLICABILITY OF METHOD Use of photochemical degradation to remove PCB’s from samples also containing chlorinated hydrocarbon pesticide residues can be a very effective method even
Peaks identified are ( 1 ) Photodegradation product of DDE, p p’-dichlorobenzophenone, (2) DDE (3) Dieldrin, and ( 4 ) DDT
Table I. Quantification of a Spiked Residue Sample Containing Aroclor 1254 and Chlorinated Hydrocarbon Pesticidesa Actual concn, ppm
Determined concn, ppm*
PCB
8.0
DDE
2.0
Dieldrin
0.7 5.0
8.2 f 1 . 0 1.8 f 0.4c 0.6 f 0.1
Compound
DDT
4.5
h 0.4
Deviations from linearity of the electron capture detector were corrected by use of a standardization plot for each compound. Average of three determinations. Concentrations represent typical levels found in samples analyzed in our laboratory. Accuracy and reproducibility may be different at other levels and ratios. Based on measurement of p,p’dichlorobenzophenone formation. a
when the PCB concentration is much larger than the individual pesticide concentrations. Total analysis time is less than one hour per sample with photolysis carried out over night. The lower limits of practical quantitation are -0.5 ppm for PCB’s and -0.05 ppm for the individual chlorinated pesticides. However, a t PCB concentrations 20-40 times the individual pesticide concentrations, pesticide analysis becomes difficult. While the pesticides we examined were easily identified and quantitated by this method, problems could arise for pesticides with short retention times ( e . g . , lindane). Also, quantification of PCB’s, whether chlorinated hydrocarbon pesticides are present or not, on the basis of one or several peaks can be somewhat inaccurate because of the inherent variation in detector response to individual isomers and since environmental samples seldom contain PCB’s identical to commercial mixtures. Received for review February 5, 1973. Accepted April 23, 1973. This research was supported in part by funds provided by the Food and Drug Administration DHEW under contract FDA 71-285 and the Michigan Agricultural Experiment Station (Article No. 6273).
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