Pesticides W . €. Westlake
U. S.
Department o f Agriculture, Beltsville, Md.
T
HIS renew covers selected references to methods of analysis for pesticides published from November 1958 to October 1960. The publications included have been examined critically and are considered to be significant contributions in the field of pesticide analysis. Many of those omitted may appear, to some workers, as important as those that are included. In a field so complex such differences of opinion are natural and desirable. An arbitrary division according to types of pesticides has been made, as in previous reviews by St. John (4.9, 50) and Westlake (54,551. During this 2-year period the development of new pesticides has continued a t about the same rate as during the previous one. The need for more sensitive and specific analytical methods has become even more acute and has stimulated research for this purpose. The availability of new and improved types of instruments has played a major part in the more significant advances. This review deals almost exclusively with micromethods since it is in this field that improvements are most urgently needed. Methods for determining pesticides in formulations and technical products are available through the Methods Clearinghouse of the Association of American Pesticide Control Officials, but no such single source is available for those suitable for residue determinations. The ninth edition of “Methods of Analysis” (44) is an excellent source for accepted methods for certain pesticides.
CLEANUP AND EXTRACTION PROCEDURES
One of the most difficult and perplexing problems in determining pesticide residues is often the extraction of the chemical from the material in which it may occur and the removal of interfering plant or animal products from the extract to permit determining the amount of pesticide present. A brief discussion of some of the studies reported in the literature seems appropriate. Anglin and McKinley (3) have reported a cleanup procedure for the removal of pigments and waxes from 88 R
ANALYTICAL CHEMISTRY
plant extracts prior to analysis for D D T and other chlorinated hydrocarbon pesticides. The waxes were precipitated from an acetone solution a t -70” C. and the pigments then removed by dissolving the residue in benzene and passing it through a Florisil column. The method is applicable to a variety of plant materials, including leafy vegetables, brassic crops, citrus, and waxy fruits. Klein (26) studied procedures for extracting organic chloride pesticides from frozen spinach. Extraction by blending with a single solvent (benzene) and mixed solvents (benzene and isopropyl alcohol), and with a Soxhlet extractor were compared. The extraction with mixed solvent that involved blending the samples with one volume of isopropyl alcohol, followed by the addition of two volumes of benzene and further blending, gave almost as good recovery of the pesticide as extraction in a Soxhlet apparatus. The single solvent extraction was decidedly inferior. I n further studies, this author (26) carried out a collaborative study of the mixed solvent method for extracting D D T and reported excellent results. It is unfortunate that the study was not expanded to include other solvent systems and mechanical procedures such as the use of anhydrous sodium sulfate in the chopped sample, followed by extraction, by tumbling, with an appropriate solvent; or blending with isopropyl alcohol followed by tumbling with benzene or other solvent, thus avoiding the hazard of blending a highly flammable mixture. The procedure employing sodium sulfate as a drying agent is preferred by many pesticide chemists, since it eliminates the blending step. It also eliminates the necessity for removing the alcohol, and extracts far less colored matter from the samples; thus, subsequent cleanup is simplified. Ford and Ottes (16) compared the Klein procedure for extracting parathion from leafy vegetables with that of the Association of Official Agricultural Chemists in which the sample is blended with water and benzene. No difference in efficiency was found, but the Klein method elimi-
nated the troublesome emulsions that complicated the AOAC method. hloddes and Cook (40) extracted crop samples for parathion and 0,Odiethyl 0-(2-isopropyl-4methyl-6-pyrimidinyl) phosphorothioate (Diazinon) analysis with acetonitrile, then extracted the acetonitrile solutions with n-pentane. If the wax content were high, the solution was passed through an alumina column. The acetonitrile was then diluted with two volumes of water and the pesticide extracted into n-pentane. The pesticides were removed on a magnesium oxide-Celite column, then eluted from the column with petroleum ether containing 10% of ethyl ether. Gutenmann and fisk (24) reported a method for extracting ethyl-N,Ndi-n-propylthiolcarbamate (EPTC) from potatoes. The tubers were blended with isopropyl alcohol and n-hexane, the solvent mixture was filtered, and the n-hexane was allowed to separate. The aqueous isopropyl alcohol was extracted with n-hexane and the wmbined extracts were analyzed by the usual method. The use of isopropyl alcohol prevented the formation of stable emulsions that are frequently encountered when extracting potatoes. The percentage of recovery of E P T C from potatoes was 93 to 95% at the 0.1 p.p.m. level. Storherr and Mills (52) developed a short e‘xtraction method for D D T determination in milk which permitted extracting and analyzing a sample in 1 day. Potassium oxalate and ethyl alcohol were added to the milk, the mixture was shaken, then ethyl ether was added. Further shaking followed, and finally, the addition of petroleum ether with a last shaking. The aqueous layer was discarded, benzene added, and the solution taken to dryntm. The butterfat was removed by partitioning between acetonitrile and petroleum ether, and further cleanup was effected by passing through a Florisil column by means of a petroleum ether-ethyl cther mixture. The extract could be used for colorimetric determination or paper chromatography. Williams (66) reported studies of a cleanup procedure for chlordane. I n
many instances the Davidow column did not remove interference. By dissolving samples in a small volume of methyl alcohol, and then chilling, waxes were removed. Treatment with dichromate-sulfuric acid, followed by passage through an alumina column, completed the cleanup for all samples except strawberries, for which no satisfactory cleanup was found. CHLORINATED HYDROCARBONS
One of the most interesting developmtnts during the past 2 years was a method for determining pesticides with a combination of gas-liquid chromatography and microcoulometric titration. Preliminary work was reported by Coulson, Cavanagh, and Stuart (I.$) and was followed by subsequent descriptions of a new apparatus and nwthod 'ny Coulson. Cavanagh, DeVries, and Walther (IS) and Coulson and Cavanagh (12). The apparatus consists of a gas chromatograph coupled directly to a quartz tube microcomh t i o n furnace that, in turn, feeds directly into a unique microcoulometric titration cell. Chloride or sulfide may be titrated continuously to permit determining either chlorine- or sulfur-contairiing pesticides. The instrument is useful for screening unknown samples since several pesticides may be determined quantitatively in one run. The procedure described will determine an amount k s s than 1 pg. of several pesticidcs and has been used for DDT, aldrin, dieldrin, BHC, malathion, parathion, denieton, and 6,7,8,9,10,10-hexachloro - 1.5,5a16,9,9a- hexahydro - 6,9mclthano - 2,4,3 - benzodioxathiepin3-oside (Thiodan). The extraction mc:thod, including partial separation of thi, pcsticides from plant materials, is given in detail. The entire procedure, frcrrii est'raction to the completion of the anslysis; can be completed in about an hour. Goodwin et al. (20) reported the use of a gas-liquid chromatograph equipped with an argon ionization detector to determine aldrin and dieldrin in vegetable extracts without cleanup. When OW npplied potentials were used, negati\,(: peaks that are characteristic of capture resulted. As little .p.m. of aldrin and 0.1 p.p.m. in gave good response. A p.Lrninary cleanup would probably :iwrc':tse the sensitivity appreciably. :'his work is of particular interest since i., icdicates the probability that the lilvrinated pesticides can be deterniined directly with the gas chromatograph without the need for other means of measurement in conjunction with it. Zweig, Archer, and Rubenstein (68) used a technique for determining residues of Thiodan with the gas chromatograph and infrared spectrophotom-
eter. These authors used the chromatograph primarily for isolation of the pesticide in a reasonably pure form. After its collection in carbon disulfide, contained in a trap attached to the chromatograph, the volume was reduced, the sample transferred to a microcell, and the spectrum scanned between 8.0 and 8.5 em.-' The method has proved satisfactory for routine use and undoubtedly can be extended to other pesticides. Mills (36) has reported a comprehensive study of paper chromatography as a means of determining chlorinated organic pesticide residues in a variety of products and has developed procedures suitable for this purpose. After solvent extraction and cleanup of the extracts by different means, it was possible to identify and approximately measure D D T , TDE, lindane, BHC, methoxychlor, DDE, toxaphene, 1,1dichloro - 2,2 - bis(p - ethylpheny1)ethane (Perthane), chlordane, heptachlor, heptachlor epoxide, dieldrin, endrin, aldrin, and 4,4'-dichloro-a(trichloromethy1)-benzhydrol (Kelthane). Mitchell (38) has developed separation procedures and determined R, values for 114 different pesticide chemicals. Two solvent systems were usedone aqueous, and one nonaqueous. The immobile solvent was applied to the paper by dipping instead of spraying to give more uniform results. The chromogenic agent was silver nitrate and Sphenoxyethanol in acetone. This paper is of value to anyone planning to use paper chromatography for organic chloride determination. McKinley and Mahon (32) have described a procedure in which Rlitchell's chromatographic techniques were applied to extracts of animal and plant samples and to several pesticides not included in previous work. A cleanup procedure for chromatographic paper is given, as well as some modifications in the immobile solvent that make the procedure more useful. Rosen and Middleton (47') have reported a method for determining chlorinated pesticides in surface waters, Carbon filters were used to remove the pesticides from large volumes of water. The eluted material was chromatographed to remove interfering organic matter and the quantity of pesticide was measured with an infrared spectrophotometer. Amounts less than 8 p.p.b. of aldrin, BHC, chlordane, T D E , DDT, dieldrin, endrin, or methoxychlor can be determined. Lisk (27) has utilized a modified Schoniger flask to determine residues of chlorinated pesticides in plant sam-. ples. Organic solvent extracts were evaporated in a cone of cellulose acetate that was burned in the flask. A special platinum holder was used, and the flask
was equipped with a side arm to which was attached a balloon to permit safe combustion. The chlorine liberated was determined spectrophotometrically by the color formed by displacement of the thiocyanate ion in the presence of ferric ion. -4bout 20 minutes was required to burn and determine the chloride in a sample, and the sensitivity was about 20 pg, The procedure has been used routinely for DDT, Thiodan, and lindane in alfalfa. Another procedure in which the Schoniger flask was used to determine the chlorine in organic compounds was reported by Olson and Krivis (45). The authors employed coulometric titration to measure the liberated chlorine. The method was rapid and accurate but did not have the sensitivity needed for most residue work. Another variation of the Schiiniger flask method has been reported by Lysyj (29). This author used the usual combustion technique and the liberated chlorine was reacted with mercuric chloranilate to produce highly colored chloranilic acid, which was measured spectrophotometrically. The sensitivity of the Lysyj procedure is about equal to that of the first method cited. Cheng (11) has described still another modification of the Schoniger flask method in which a mercurimetric titration in an alcohol-water solvent was employed. The end point is made more discernible by the use of the mixed solvent system. Baker and Skerrett (4) have reported a procedure for determining D D T and ethyl 4,4'-dichlorobenzilate (Chlorobenzilate) when they occur togethrr in spray deposits. An alumina column was used to separate the two conipounds, after which analyses were made by appropriate colorimetric methods. The separation prior to analysis climinated the need for the correction factors that have been used when the two compounds were determined in the presence of one another. Rosenthal, Gordon, and Stanley (48) have developed a method for determining residues of TDE in plant extracts. The residues were dehydrohalogenated by means of sodium ethylate in dimethylformamide after the necessary extraction and cleanup procedures. Treatment of the resulting alkene with sulfuric acid yielded an intensely colored carbonium ion complex. As little as 5 pg. can be measured. A method for determining heptachlor epoxide in fat and milk was reported by Meyer, Malina, and Polen (35). The reagent originally developed for heptachlor is also a color-forming reagent for the epoxide. Separation techniques for removing the compound from fat and other animal products were given. The maximum absorption of the colored product is a t about 417 mp, VOL. 33, NO. 5, APRIL 1961
89 R
which is in the region in which many interfering products in the extracts also absorb strongly. E\treme care is necessary to avoid differences in readings that may be interpreted as indicating the presence of heptachlor epoxide but are actually variations in the background caused by other compounds in the sample extract. Gunther, Blinn, and Barkley (22) have described a method for determining residues of 2,4,4’,5-tetrachlorodiphenyl sulfone (Tedion) in citrus fruit peel by means of the infrared spectrophotometer. Extracts of the peel were oxidized nitf, chromic anhydride in acetic acid to minimize interferences from natural products. The strong absorption peak exhibited by Tedion a t 1160 cm.-‘ was used, and as little as 20 pg. may be determined in 100 grams of peel. Graupner and Dunn (21) have reported a method for determining residues of toxaphene by means of fusion with diphenylamine in the presence of zinc chloride. The reaction product from the fusion was dissolved in acetone or glacial acetic acid and determined spectrophotometrically. The range of the method was from 20 to 700 pg., but with care as little as 10 pg. can be determined with good reliability. Cleanup procedures were given to permit use of the method for various crops and foods, as well as for formulations. The method is not specific but can be used whenever other organic chlorides are not present. Cueto (16) has described the use of the reaction of dieldrin with diphenylamine in the presence of zinc chloride for determining this pesticide in animal fat. The value of the method is questionable since it is not specific and is less sensitive than the phenyl azide method commonly used. I t is, however, less tedious than other methods and may have some application where specificity is not required. Brumbaugh and Stallard ( I O ) have developed a sensitive colorimetric method for determining perchloroethylene in wheat. The grain was digested in a specially designed apparatus, the perchloroethylene absorbed in pyridine, aniline added, and the solution refluxed. Sodium hydroxide was added while the solution was refluxing and an orange color developed. The method is not specific but may be used in the absence of other halogenated compounds. ORGANOPHOSPHORUS C O M P O U N D S
McCaulley and Cook (SO) recorded the infrared spectra of organophosphorus pesticides and developed a procedure suitable for identification and semiquantitative determination. To remove part of the plant materials, samples were extracted with acetonitrile, followed by extraction of the acetonitrile 90 R
ANALYTICAL CHEMISTRY
solution nith iso-octane. For further Giang and Schechter (19) have develpurification of some materials, distillaoped a method for determining the tion v a s used, whereas for others a residues of phorate and its insecticidally Florisil column was employed. The active metabolites. The samples were order of elution of different pesticides extracted with chloroform and the exfrom the column is given. There is tract was oxidized nith perbenzoic acid some excellent information on cleanup to convert the pesticide and metabolites procedures in this paper, in addition to the phorate oxygen analog sulfone. to the infrared curves and details of This compound was then hydrolyzed methods used for detection of the comto liberate formaldehyde that was repounds. acted uith chromotropic acid. The resulting colored complex was read on Anderson, Adams, and MacDougall a spectrophotometer. The method is ( 2 ) developed a method of analysis for sensitive to about 10 pg. 0 - (3 - chloro - 4 - methylumbelliferone) 0,O-diethyl phosphorothioate (Co-Ral) Patchett and Batchelder (46) have and its oxygen analog in animal tissues reported a method for determining S - ( p - chloropheny1thio)methyl 0,Othat was based upon the fluorescence of the product formed upon alkaline diethyl phosphorodithioate (Trithion) in crop tissues. A two-phase acetic hydrolysis. The sensitivity of the method is limited only by the backacid-hydrogen peroside-benzene system ground fluorescence of untreated samWBP used to oxidize the compound to strong cholinesterase inhibitors. Deterples. I n fat and meat this background mination was based on the inhibition is about 0.02 p.p.m. Extraction and of cholinesterase in human blood serum, cleanup procedures are given in detail. with a sensitivity of 0.01 pg or less. Boyd (9) modified the cholinesteraseinhibition procedure commonly used for compounds that inhibit the action CARBAMATES of the enzyme to determine residues of 0-2,4dichlorophenyl 0,O-diethyl phosMiskus, Gordon, and George (37) phorothioate (VC 13 Nemacide). The have developed a method for deterniinmodifications, although relatively ing residues of 1-naphthyl-AT-methylminor, simplified the procedure to carbamate (Sevin) in different crops. permit routine analysis of many samples Alkaline hydrolysis of S e d n produced in a minimum of time. Extraction and 1-naphthol, which was reacted with cleanup methods are giren in detail. p-nitrobenzenediazonium fluoborate to The method is sensitive to less than 0.01 produce an intense color with maximum absorbance a t 590 mp. The range of Pg. Sorris and Kuchar (43) have reported the method is 5 to 40 pg. of Sevin. a method for determining malathion Simplicity and speed are the outstandresidues in cottonseed. This method ing points in favor of this method. is essentially the same as that published A method for determining residues earlier by these authors, but with a of isopropyl A’-phenylcarbamate ‘TPC) suitable cleanup procedure added. The in plant tissues was reported by Montseed is extracted with n-hexane and gomery and Freed (41). The IPC partitioned into acetonitrile, then put is hydrolyzed in alkali to produce anithrough a column of alumina. The line, which is coupled with X-l-naphmethod is sensitive to about 20 pg. thylethylenediamine dihydrochloride to and should be applicable to other oily produce a colored compound. The products. method is sensitive to about 0.1 p.p.m. Giang and Schechter (18) have deof IPC. scribed a method for determining 0,OBatchelder and Patchett ( 6 ) have dimethyl S- [4-0~0-1,2,3-benzotriazin-3- developed a method for determining (4H)-3 lmethyl] phosphorothioate EPTC in crops and soils. The EPTC (Guthion) residues in cottonseed. Exwas hydrolyzed to di-n-propylamine traction with chloroform was followed which was reacted with carbon disulfide by separation of the pesticide from plant in the presence of ammonia and cupric materials by chromatographing on an sulfate to form the cupric dithiocaralumina column with n-pentane and bamate complex. The method is acetonitrile. -4cid hydrolysis liberated sensitive to about 5 pg. 1IcKinley formaldehyde which was distilled and and hIagarvey ( S I ) have reported a determined colorimetrically by reaction paper chromatographic procedure for with chromotropic acid. The sensitivity resolving six dithiocarbamates into of the method is about 2 fig. Another two groups, and tests to identify the colorimetric method for determining individual carbamates. A technique Guthion residues was reported by is also described that distinguishes pestihleagher et al. (38). The pesticide cides possessing thioketone or merwas hydrolyzed to form anthranilic captan groups from others. acid, then diazotized, and coupled with N-1-naphthylethylenediamine dihydroMISCELLANEOUS chloride. Cleanup procedures are given for cottonseed, cole crops, fruit, and Barry and Lisk (5) reported a method for determining residues of 2,4-dichloromilk.
Go-c.hloroanilino-s-triazine (Dyrene) i n apples, bnsed on the Zincke reaction. Cleanup of the extract’s was accomplished on an alumina column prior l o reaction with pyridine and alkali which produced a colored solution. About 5 pg. can be determined in a 100-gram sample. Meagher et al. (34) have also reported a method for del ermining residues of this fungicide I)?. hydrolysis to produce o-chloroaniline n-likh was diazotized and coupled with ~-1-nn~)htiiylrLhylenediamine dihydrochloride to produce a colored complex. The method was tested for celery, p0tatoi.q and tomatoes. Becknian and Feldman ( 7 ) have reported n. method for determining piperazine in feeds. The compound was rst,ractcd into dilute acid and clarified, t1ir.n rezcted, in alkaline solution, with 1,4-benzoquinone to produce a redorange color. The procedure requires :ihout 100 pg. of the compound for best results. Rownian, Beroza, and Acree (8)developt4 a method for determining Zethyl1.R-iiesanediol that was based upon the reaction with concentrated sulfuric acid and p-tlimet!iylaminobenzaldehyde to give a colored product. The method is sensitive to about 5 pg. and was tested for use in tlet,ermining the compound on glass. cloth, and human skin. Munday (42) used the reaction of chroniotropic acid and formaldehyde to determine residues of piperonyl butoxide in wheat. After removal of oils and waxw hy saponification with methanolic potassium hydroxide, and extraction into petroleum ether, the formaldehyde was liberated by hydrolysis with strong su!furic arid. -4 sensitivity of about. 10 pg. was achieved. Gutenmanvi and Lisk (25) employed f ? i e moc:ific;d Schoniger flask for the cm!i)t&io:l of dried apple tissue prior mining mercury. Loss of the rLlt’r(’!iry by volatilization as elimi. ?;be of the closed flask. Apple i s Il:-ied on cellophane overnight under vacuum. then burned in t)heflask. The mer\ !iTy was determined spectro:.li~tc,metric;t!13’after extraction of the n korbing solution with dithizone. A . h v + 12 samples can he burned and :innlyzed in a day. L,isk (28) has reported a procedure for cletermining arsenic in potatoes. mple was ashed with magnesium nitrate and the ash extracted with acid. Acid niolybdate was added, followed by extraction with a l-butanol-chloroform mixture to remove interfering phosph:ttrs 8s molybdophosphoric acid. The arsenic was extracted as molybdoarsenic acid with I-butanol, acidified with sulfuric acid, and reduced to the heteropoly blue with stannous chloride in ethyl alcohol. The range of the method is from less than 1 to about 50 pg. Frehse and Tietz (17) have also
reported a method for determining arsenic in plant materials using the molybdenum blue reaction preceded by wet ashing and distillation in a special apparatus. The procedure will easily determine as little as 1 pg. of arsenic and may be used for any plant tissue that can be satisfactorily wet-ashed. Mitchell (59)has developed a procedure for separating and identifying 6 arseno-organic compounds by paper chromatography. Two-dimensional chromatography was employed to separate the compounds, which are then located in the chromatogram by ultraviQlet light, blueprinting, or by a chromogenic agent. Arsanilic acid, arsenosobenzene, arsphenamine, 3-nitro4-hydroxyphenylarsonic acid, 4nitrophenylarsonic acid, and p-ureidobenzenearsonic acid were studied. Thomas (55) has used the gas chromatograph, with argon ionization detector, to determine diphenyl and o-phenylphenol in concentrated orange juice. A preliminary distillation is required to remove interfering compounds, after which quantities in the range of 2 to 4 p.p.m. can be determined. The herbicide, I-chloro-8nitrobenzene, was determined by Young (57) in pineapple by reduction, diazotization, and coupling with N-l-naphthylethylenediamine dihydrochloride to form a colored compound which was determined spectrophotometrically, Residues in the 0.01-p.p.m. range can be determined. M e n s , Haenni, and Fulton ( 1 ) have developed a procedure for determining dichlorodifluoromethane and ethylene oxide in fumigation mixtures of these two compounds. The dichlorodifluoromethane was determined by a thermal conductivity method, with a commercially available gas-analysis instrument. The ethylene oxide was absorbed in normal sulfuric acid and the excess acid was back-titrated with standard alkali. LITERATURE CITED
( 1 ) Affem, W. A., Haenni, E. O., Fulton, R. A., ANAL.CHEM.31, 1565 (1959). ( 2 ) Anderson, C. A., Adams, J. M., MacDougall, D., J . Agr. Food Chem. 7 , 256 (1959). (3) Anglin, C., McKinley, W. P., Zbid., 8, 186 (1960). (4) Baker, E. A., Skerrett, E. J., Analyst 83, 447 (1958). ( 5 ) Barry, D. L., Lisk, D. J., J . Agr. Food Chem. 7 , 560 (1959). (6) Batchelder, G. H., Patchett, G. G., Zbid. , 8, 214 (1960). (7) Beckman, H. F., Feldman, L., Zbid., 8, 227 (1960). (8) Bowman, M. C., Beroza, M., Acree, F., Zbid., 7, 259 (1959). ( 9 ) Boyd, G. R., Ibid., 7 , 615 (1959). (10) Brumbaugh, J. H., Stallard, D. E., Ibid., 6 , 4 6 5 (1958). (11) Cheng, F. W., Microchem. J . 3, 537 (1959). (12) Coulson, D. M., Cavanagh, L. A,, ANAL.CHEM. 32, 1245 (1960).
(13) Coulson, D. M., Cavanagh, L. A., DeVries, J. E., Walther, B., J . Agr. Food Chem. 8 , 399 (1960). (14) Coulson, D. M., Cavanagh, L. h., Stuart, J., Ibid., 7. 250 (1959). (15) Cueto,‘C., Zbid.’, 8, 273 (1960). (16) Ford, L. A., Ottes, R. T., J . Assoc. Ofic. Agr. Chemists 43, 700 (1960). (17) Frehse, H., Tietz, H., J . Agr. Food Chem. 7, 553 (1959). (18) Giang, P. A., Schechter, M. S., Zbid., 6 , 845 (1958). (19) Zbid., 8,,51 (1960). (20) Goodwin, E. S., Goulden, R., Richardson, A., Reynolds, J. G., Chem. & Znd. (London) 1960, 1220. (21) Graupner, A. J., Dunn, C. L., J . Agr. Food Chem. 8, 286 (1960). (22) Gunther, F. A., Blinn, R. C., Barkley, J. H., Zbid. 7, 104 (1959). (23) Gutenmann, W. H., Lisk, D. J., Zbid., 8 , 306 (1960). (24) Ibid., p. 216. (25) Klein, A. K., J . Assoc. Ofic. Agr. Chemists 41, 551 (1958). (26) Zbid., 43, 703 (1960). (27) Lisk, D. J., J . Agr. Food Chern. 8 , 119 (1960). 0 (28) Zbid., p. 121. (29) Lysyj, I.,Microchem. J . 3,529 (1959). (30) McCaulley, D. F., Cook, J. W., J . Assoc. Ofic. Agr. Chemists 43, 710 (1960). (31) McKinley, W. P., Magarvey, S. A., Zbid. , 43, 717 (1960). (32) McKinley, W. P., Mahon, J. H., Ibid., 42, 725 (1959). (33) Meagher, W. R., Adams, J. M., Anderson, C. A., MacDougall, D., J . Agr. Food Chem. 8 , 282 (1960). (34) Meagher, W: R., Anderson, C. A., Gonter, E., Smith, S. E., MacDougall, D. ,Zbid., 7, 558 (1959). (35) Meyer, C. F., Malina, M. A., Polen, P., Zbid., 8, 183 (1960). (36) Mills, P. A., J . Assoc. Ofic. Agr. Chemists 42, 734 (1959). (37) Miskus, R., Gordon, H. T., George, D. A., J . Agr. Food Chem. 7 , 613 (1959). (38) Mitchell, L. C., J . Assoc. O&. Agr. Chemists 41, 781 (1958). (39) Zbid., 42, 684 (1959). (40) Moddes, R. E. J., Cook, J. W., Zbid., 42, 208 (1959). (41) Montgomery, M., Freed, V . H., J . Agr. Food Chem. 7 , 617 (1959). (42) Munday, W. H., J . Assoc. Ofic. Agr. Chemists 43, 707 (1960). (43) Norris, M. V., Kuchar, E. J., J . Agr. Food Chem. 7, 488 (1959). (44) “Official Methods of Analysis of the
Assoc. Offic. Agr. Chemists,” 9th ed., William Horwitz, ed., Washington, D. C., 1960. (45) Olson, E. C., Krivis, A. J., Micro-
chem. J . 4, 181 (1960). (46) Patchett, G. G., Batchelder, G. H., J . Agr. Food Chem. 8 , 54 (1960). (47) Rosen, -4.A., Middleton, F. M., ANAL.CHEM.31, 1729 (1959) (48) Rosenthal, I., Gordon, C. F., Stanley, E. L., J . Agr. Food Chem. 7 , 4 8 6 (1959). (49) St. John, J. L., ANAL.CHEM.25, 42 11953). (50) Z&d., 27, 654 (1955). (51) Smith, G. N., J. Agr. Food Chem. 8 , 224 11960). (52) Storherr, R. W., Mills, P. A., J . Assoc. O@. Agr. Chemists 4 3 , 8 1 (1960). (53) Thomas, R., Analyst 85, 551 (1960). (54) Westlake, W. E., ANAL.CHEM.29, 679 (1957). (55) Ibid., 31, 724 (1959). (56) Williams, D. W., J.Assoc. O&. Agr. Chemists 41, 569 (1958). (57) Young, H. Y., J . Agr. Food Chem. 8 , 213 (1960). (58) Zweig, G., Archer, T. E., Rubenstein, D., Zbid., 8, 403 (1960). VOL 33, NO. 5, APRIL 1961
0
91 R
