ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
in most biological materials, the Al/Ca concentration ratio is typically far less than unity. In view of the fact that the ratio must exceed approximately 2-3 (Figure 1) before the suppression effect becomes significant, the effect may be regarded as unimportant for the above types of samples. These evaluations generally indicate that solute vaporization interference effects are generally of minimal significance for the three-electrode dc plasma system used. This observation indicates that the three-electrode design change has been instrumental in eliminating interferences effects found to be significant for the two-electrode system ( I I ) .
LITERATURE CITED
2405
T. C. Rains, ref. 1, Chapter 12. D. J. David in "Flame Emission and Atomic Absorption spectrometry", J. A. Dean and T. C. Rains, Eds., Vol. 111, Marcel Dekker, New York, 1975, Chapter 2. E. M. Bulewicz and P. J. Padley, Spectrochim. Acta, Part B , 28, 125 (1973). Roland Herrmann and C. T. J. Alkemade, "Chemical Analysis by Flame Photometry", Interscience, New York, 1963. M. Marinkovic and B. Dimitrijevic, Spectrocheim. Acta, Part 6 ,23, 257 (1968). W. E. Rippetoe, E. R. Johnson, and T. J. Vickers, A m i . Chem., 47, 436 (1975). R . K. Skogerboe and I. T. Urasa, Appl. Spectrosc. 32, 527 (1978). Hugo L. Felkel and Harry L. Pardue, Anal. Chem., 50, 602 (1978). G. W . Johnson, H. E. Taylor, and R. K. Skogerboe, Spectrochim. Acta, Part B , 34, 197 (1979). (14) Joseph Reednick, A m . Lab., 11(3), 53-62 (1979).
C. T. J. Alkamade in "Flame Emission and Atomic Absorption Spectrometry", J. A. Dean and T. C. Rains, Eds., Vol. I, Marcel Dekker, New York, 1969, Chapter 4. R. N. Kniseley, ref. 1. Chapter 6. A. N. Hambly and C. S. Rann, ref. 1, Chapter 8. Ivan Rubeska, ref. 1, Chapter 11.
RECEIVED for review June 1, 1959. Accepted August 24, 1979. This investigation was partially supported by the Water Resources Division of the U S . Geological Survey.
Loss of Polychlorinated Biphenyl Homologues during Chromium Trioxide Extraction of Fish Tissue Michael J. Szelewski, David R. Hill, Stuart J. Spiegel," and Edwin C. Tifft, Jr. O'Brien & Gere Engineers, Inc., 1304 Buckley Road, Syracuse, New York 13221
Polychlorinated biphenyls (PCBs) are synthetic organic compounds produced by the chlorination of biphenyls. There are 209 possible chlorobiphenyls containing from one to ten atoms of chlorine ( I ) . These compounds are homologues, various mixtures of which are registered in the United States by the Monsanto Chemical Company under the trade name, Aroclor. The compounds are characterized by relative nonflammability, and useful heat exchange and dielectric (insulating) properties, the primary purpose for their development in 1929. They have been found to be toxic to a variet,y of organisms, although the greatest danger may be presented by the phenomenon of bioaccumulation, or bioconcentration, in the environment as the containment is traced through the food chain (1). Chemical characteristics of the individual compounds and Aroclors are dependent upon the degree of chlorination. Identification of the PCB mixture is by numerical nomenclature, for example, Aroclor 1221, Aroclor 1242, etc., with the number indicating the structure and composition of the compound. The first two digits represent the type of molecule - 12 = chlorinated biphenyl, 54 = chlorinated terphenyl. The last two digits give the average percentage, by weight, of chlorine. The exception to this nomenclature is Aroclor 1016 which contains 41% chlorine by weight, but in which the penta-, hexa-, and heptachlorobiphenyl content has been significantly reduced from Aroclor 1242. The analysis of environmental samples for polychlorinated biphenyls can be complicated by the presence of organochlorine pesticide residues, which are characterized by gas chromatographic (GC) retention times identical with many PCB homologues. One of the established methodologies for the identification and quantitation of PCBs in animal tissue in the presence of organochlorine pesticides, such as DDE, includes a preparative step involving chromic acid digestion (1-3). The purpose of this step is to oxidize these sources of interference. 0003-2700/79/0351-2405$01 OO/O
In this work, the chromic acid treatment was being employed in the analysis of freshwater and marine fish for PCBs when an alteration of Aroclor chromatographic patterns was observed. These alterations included changes in expected peak areas and the disappearance of several PCB homologues. A confirmatory investigation was performed under controlled conditions to discover the extent of the effect.
EXPERIMENTAL A Tracor model 550 gas chromatograph equipped with a model 700 Hall electrolytic conductivity detector was used in this study (Tracor, Austin, Tex.). The GC was interfaced to a HewlettPackard (Palo Alto, Calif.) model 33808 integrator. The chromatographic column was 183 cm long, 6.4-mm 0.d. by 4-mm i.d., glass, and packed with 3% OV-1 on 80-100 mesh Chromosorb W-HP (Applied Science Laboratories, State College, Pa.). The column was conditioned at 275 "C, 50 mL/min N2 until satisfactory resolution and response were obtained. Operating temperatures for the GC were: furnace, 850 "C; column, 190 "C; inlet, 225 "C; outlet, 250 "C, and auxiliary, 260 "C. The carrier flow was 50 mL/min N2 at 3.5 kg/cm2; the reaction flow, 50 mL/min H2 at 0.7 kg/cm2. All solvents were spectrograde (Mallinckrodt, St. Louis, Mo.) without further purification, while other reagents were reagent grade. The chromic acid solution was prepared by dissolving 135 g of chromium trioxide in 90 mL of water and adding 750 mL of glacial acetic acid ( 3 ) . Twenty-five milliliters of Cr203solution was added to each of fifteen 5-mL hexane solutions containing prepared Aroclor standards, as follows: eight replicates of Aroclors 1016 and 1254, respectively,and six replicates of both Aroclor 1221 arid a mixture containing all three Aroclors in equivalent concentrations. The solutions were heated at 90-100 "C for 45 min with constant stirring and the addition of Cr203solutions as necessary to maintain an excess quantity of oxidant in the solution. After heating, each solution was added to 100 mL of water, respectively, and extracted four times with petroleum ether, with removal of the aqueous phase after each extraction. The organic 1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
Table I. Theoretical vs. Experimental Aroclor Concentrations (Post-Treatment) for Low-Level Spiked Samples Subjected to Chromium Trioxide Treatment
sample
Aroclor
concentration, PgIL, PPb theoret- experi- recovery, 9% menta I ical
recovery, %
100 000
40 000
40
1 0 0 000 100 000 100000
87 000 8 4 000 90 000
87 84 90
0 0 0
5 6
-
1221 1221 1221
100 000 1 0 0 000 1 0 0 000
(10 000
