Review of APPLIED
PESTICIDES W. E. Westlake U. S. Department of Agriculture, Beltsville, Md.
T
biennial review covers selected references dealing with methods of analysis for pesticides published from h’ovember 1956 to October 1958. An attempt has been made to include only publications that make significant contributions in the field of pesticide analysis. An arbitrary division according to type of pesticide has been made, as has been done in previous reviews by St. John (85, 86) and Kestlake (100). Many new pesticides have been introduced during the two-year period, and a considerable number have come into general use during this time. The requirements set forth in Public Law 518 (Miller Amendment) appear not to have seriously hindered the development and introduction of new pesticides and probably have accelerated the development of analytical methods suitable for residue determinations. This review deals principally with micromethods, as it is in this field that work is most urgently needed and most contributions have been made. Macromethods for the determinations of pesticides in formulations and technical products are available through the hlethods Clearinghouse of the Association of American Pesticide Control Officials, but no such source is available for micromethods suitable for residue determinations. One excellent source of information is the book, edited by Metcalf (68), which contains an excellent chapter on “Chemical Analysis of Pesticide Residues,” n ith 462 references. Another chapter, “Bioassay of Pesticide Residues,” with 112 references, is of value to analysts. Dewey (29) has also presented a review of bioassay techniques for quantitative determination of pesticide residues, and an excellent discussion of procedures. The problem of securing adequate samples for residue analysis, 17 hile perHIS
724
ANALYTICAL CHEMISTRY
haps not considered a part of the analytical procedure by many chemists, is of great importance in their work, for the ultimate value of the analysis is dependent upon the sample’s being representative of the product being analyzed. Lykken, hlitchell, and Woogerd (61) have presented a n excellent and detailed discussion of sampling problems and procedures for a variety of crops including fruits, vegetables, nuts, grains, and forage. The necessity for participation of the residue chemist in sampling, to the extent necessary to secure adequate samples, cannot be emphasized too strongly. The importance of the cleanup procedures preceding actual analysis liken ise inust not be overlooked. The determination of microgram quantities requires analytical methods of extreme sensitivity and precision 15-hich, for the most part, are reliable only in the absence of any significant amount of plant or animal products. Virtually every paper on methods for residue determination includes details of the necessary cleanup steps. Only too often, however, the procedures are unsatisfactory in the hands of other workers because of variations in adsorbents, solvents used, crops, or animal products. Kork is urgently needed to develop universal procedures which can be followed by all workers. One step in this direction n-ould be the development of chromatographic adsorbents of standard actirity. Lindsey, Pash, and Stanbury (60) have developed a method for preparing alumina of standard activity for this purpose. CHLORINATED HYDROCARBONS
General. Slthough it is generally preferable t o use a method of analysis t h a t is as specific as possible, for a
given compound, the determination of total organic chlorine is widely used for t h e determination of chlorinated hydrocarbon pesticide residues and is a very valuable procedure. Efforts are being made by many workers t o improve the speed and sensitivity of this type of analysis. Of particular interest is the colorimetric method for determining chlorine, based on the displacement of the thiocyanate ion from mercuric thiocyanate by the chloride ion. Zall, Fisher, and Garner (10.9)have developed a method whereby concentrations as low as 0.05 p.p.m. can be determined. Bergniann and Sanik ( 8 ) have presented a procedure, using the same reaction, for determining trace amounts of chlorine in naphtha, which should prove useful, following combustion of chlorinated hydrocarbons in the quartz tube conibustion furnace. The method is sensitive to 0.5 yand is accurate to 0.5 y in the 1-to 100 y range. Iwasaki, Utsumi, Hagino. and Ozawa (47‘) developed two modifications of the same method. Another version of the same procedure was given by Swain (91), who notes that the phosphate ion interferes but other common ions do not. The procedures employ ferric iron to form a colored complex with the liberated thiocyanate, rrhicli can be determined by the absorption a t 460 mp. Another procedure, slightly lms sensitive, vias presented by Bertolacini and Barney (9), uho used mercuric chloranilate to form a colored complex with the chloride ion. The absorption peak is a t 305 mp, requiring a spectrophotometer suitable for the ultraviolet range. Anions interfere to some extent, but not seriously. Cations interfere but may be removed with a resin column. A method for total chlorine determination by reduction with a liquid anhydrous ammonia-sodium mixture was given by Beckman, Ibert, Adams, and
Skovliii ( 7 ) . An advantage of this method is tlie extreme rapidity-lOO% dechlorination being accomplished in 2 to 3 minutes. The method was applied t o forniulations but should be readily adaptable to residues. Chapman and Sherwood (23) used disodiunl diphenyl to convert to inorganic chlorine, then reacted with palladous sulfate and measured the absorbance at’ 230 mp. A sensitivity of 1 to 10 y is claimed. It is possible to separate halides by selective oxidation and thus determine bromine, chlorine, and iodine individually. Kat0 and Shinura (49) addcd silver dichromate to the solution containing the chloride ion and determined the liberated chromate ion by the absorbance a t 366 or 405 mp. It is claimed that as little as 1 y can be detected. \Vest and Coll (99) utilized the intense absorption band a t 340 mp, of iron perchlorate, to measure the chloride ion content. The method is relatively free of interferences, except large amounts of sulfate. Chlorine can be determined in the presence of other halides. Hudy and Dunn (46) have developed a vertical quartz-tube combustion furnace which permits the burning of large samples. -4s much as 10 to 20 grams of fat, or oil can be burned. The chloride It-as determined amperometrically. h f a p t ~and Shrader (64) used a combustion furnace t’o determine organic chlorine and bromine in fumigants. The fumigants were recovered by aerating a watrr suspension of the sample and the gases were all burned and absorbed. drration of the water suspension of samplrs gave much better recovery than dry aeration. Hornstein (4%’)investigated the use of a granulated zinc column for determining chlorinated organic hydrocarbon insecticides. An acidified solution of the insecticide was percolated through the column. The chlorine removed is a function of the molecular structure and is (*onstant for any one compound. The per cent of chlorine removed, and conwrsion factors for the common chlorineconhining insecticides, are given. The nicthod is applicable to the analysis of forniulations and technical products. Conroy, Munsey, and Ramsey (26) have developed a procedure for halide deterniination in fumigants using ethanolamine-sodium reduction. The fumigant is removed by distillation from acidified water, and the compound is absorbed in a mixture of 1,4-dioxane and ethanolamine (5 to 1). I n both of the last tn.0 methods, bromine is determined by the Kolthoff-Yutzy-van der Meulen method, total halide by the Volhard technique, and chlorine by the difference. Specific Methods. The infrared analysis of mixtures of isomeric or closely related substances was studied by McDonald and Watson (63), and
the technique of differential analysis was successfully applied, Methods were developed for the determination of mixtures of benzene hexachloride, lindane, DDT, TDE, and Ovex. The procedure should be useful for the analysis of formulations. Mitchell (7.9) reported the use of a solution of silver nitrate and 2-phenoxyethanol in aqueous ethanol as a chromogenic agent for the detection of pesticides on chromatograms, Of 40 pesticides, chiefly chlorinated, 37 could be detected in microgram or microliter quantities. In general, 5 y or 5 71. were sufficient. AIitchell (71) also has presented a detailed paper chroniatographic procedure for separation and identification of technical D D T ; p,p’-DDT; DDA; D D D ; D D E ; 4,4’-dichlorobenzophenone; and 2,-l-dicblorohenzophenone. Six of the 7 conipounds can be separated by their order of separation on the chromatogram. The order and distance from one another are constant regardless of uncontrollable variables. Burchfield and Schuldt (80) have developed a colorinietric method for determining pesticides containing active halogen atoms, based on their reaction with pyridine in alcohol. Qualitative tests were developed for s-triazines; l-fluoro-2,4-dinitrobenzene, 3,4-dichlorotetrahydrothiophene-1,l-dioxide; trichloroacetic acid, and Captan. Qualitative tests \\-ere developed for heptachlor, lindane, chlordan, toxaphen, tlichlone, Spergon, and others. The nonspecificity of the method gives it tlie advantage of general applicability where a specific test is not required. Roth (84) reported a method utilizing the Schechter method for determining both D D T and chlorobenzilate in mixtures, on a single solution. The color due to chlorobenzilate vias read with a KO.54 filter and that due to D D T with a KO. 66 filter. Correction was niade for mutual interference. Austin, Bonner, and Epps (3) and Bunger and Richburg (18) have reported similar infrared techniques for the determination of D D T and benzene heuachloride in cotton dusts. The methods are simple and rapid, employing carbon disulfide as the solvent, and using a direct extraction of the dusts. Benzene Hexachloride and Lindane. Bradbury and Standen (12) noted t h a t benzene hexachloride may be determined in the presence of pentachlorocyclohexene, by the nitration procedure, as the latter compound is converted to tetrachloroadipic acid. Braid and LeBouf (1%’)used infrared spectrophotometry to determine trace amounts of lindane in air. The lindane was adsorbed on alumina, then removed with hot iso-octane, concentrated, and read in a 0.5-ml. volume. A mininiuni of about 50 y can be determined. Lichtenstein, Beck, and Schulz (58) have re-
ported using the method of Schechter and Hornstein for lindane determination in soils, introducing the sample directly into the reaction flasks, rather than extracting prior to analysis. Distillation of a portion of the acetic acid from the sample before analysis, as has been the practice with other types of samples, removed interfering materials, and the reaction could be carried out without difficulty. Cohen (24) has developed a method of cleanup and extraction for fruits and vegetables that permits the use of Mitchell’s technique for distinguishing between lindane and technical benzene hexachloride by paper chromatography. Treatment n i t h fuming sulfuric acid and partitioning betn-een n-hexane and acetonitrile n-ere employed in the procedure. Recoveries of 85% of the lindane and 72% of the benzene hexachloride resulted. Hornstein (45) has developed a method for determining the y-benzene hexachloride content of technical inaterial by the radioisotope dilution method. The procedure gave excellent results although not practical for routine investigations or control work. p - Chlorobenzyl p- Chlorophenyl Sulfide. Gunther, Rlinn, and Barnes (37) have developed an infrared method for determining p-chlorobenzyl p-chlorophenyl sulfide, and its oxidation product, the sulfone, on pears. The miticide, in carbon disulfide, gives a line with a slope of 550 y per 0.1 absorbance unit, in a volume of 1 ml. The sulfide was determined at 1094 em.-’ and the sulfone a t 1155 em.-’ A colorimetric procedure for determining this conipound was developed by Hardon, Brunink, and van der Pol (Sa),utilizing the reaction 1% ith m-dinitrobenzene in alkaline solution to give a colored conipound Ithich Ita4 read a t 510 m p . DDT does not mterfere. Apple estracts were oxidized with chromium trioxide to remove n ayes, extracted into ether, and taken to dryness. Watson (97) determined this miticide, utilizing a strong absorption peak a t 262 nip, for direct spectrophotometric determination. The sulfoxide was also determined by reducing it to the sulfide with tin and hydrochloric acid. Chromatographing with alumina removed most of the interfering materials. The sensitivity was about 50 y in 10-nil. final volume, and reducing the volume should increase the qensitivity. Of the three methods, that of Hardon, Brunink, and van der Pol possesses the highest degree of sensitivity and appears best suited for the average residue laboratory. The infrared method could be made more sensitive by the use of microcells and a smaller volume, although the removal of interfering materials might become a major problem for some types of samples. Toxaphene. Hornstein (43) has presented a colorimetric method for VOL. 31, NO. 4, APRIL 1959
725
determining Toxaphene or Strobane by reaction with thiourea in alkali t o give a yelloa color. Chlordan and heptachlor interfere. T h e sensitivity is about 0.5 mg. of Toxaphene or 0.25 mg. of Strobane, using a final volume of 5 ml. Absorbance was determined at 400 mp. The method is not sensitive enough for most residue work. Hercules Powder Co. (39) has developed a colorimetric method based on the green color produced when Toxaphene is fused with diphenylamine and zinc chloride. An acid treatment and chromatography are used for cleanup prior to the fusion, and the method is applicable to a variety of products. The accuracy is good in the 1 to 100 y range, making the method suitable for residue analysis. At least two other pesticides, chlordan and Thiodan, interfere. Kelthane. Gunther and Blinn (36) have developed an ultraviolet spectrophotometric method for 4,4’-dichloro - a - (trichloromethyl) - benzhydrol (Kelthane) utilizing its absorption a t 264 mp. It may also be determined indirectly by the absorption of its 2,4-dinitrophenylhydrazone in alcoholic alkali a t 510 mp. For residues, oxidation of extraneous material with chromic anhydride is recommended. In citrus peel, as little as 10 y can be determined. Rosenthal, Frisone, and Gunther (82) employed a mild alkaline hydrolysis to liberate chloroform nhich was recovered in a special apparatus and converted to a Fujiwara-type red dye with a pyridinewater-sodium hydroxide mixture. The absorbance was determined to 530 mp, and the sensitivity was found to be about 10 y. Heptachlor and Chlordan. Jorgensen (48) reported on modifications of the established micromethod for determining heptachlor. The most important development was in the cleanup procedure which included freezing out of waxes in methanol, and the use of the Davidom column following this. The Davidow reagent n-as substituted for the Polen-Silverman reagent for developing the color. Williams (101) investigated cleanup procedures for chlordan prior to colorimetric determination. H e also employed the freezing technique to remove waxes, followed by passage through the Davidow column. Miscellaneous. p-Ch1orophenyl-pchlorobenzenesulfonate (Ovex) was determined by Butzler, Luce, and Wing (26) by a colorimetric method sensitive to less than 5 y. Ovex is hydrolyzed to p-chlorophenyl and sodium benzenesulfonate, the p-chlorophenyl is recovered by steam distillation, nitrosated, and chromatographed, and its absorbance is measured a t 430 mp. Interfering colored compounds are eliminated by the chromatographing. Shuman (89) has proposed a modification
726
ANALYTICAL CHEMISTRY
of the Patchett method for determining residues of p-chlorophenyl phenyl sulfone (Sulphenone) on apples, pears, and peaches. The fruit is stripped with hexane, and the insecticide is partitioned into acetonitrile, and chromatographed to isolate the Sulphenone from other ultraviolet absorbing compounds. The residue is dissolved in iso-octane and the absorbance is determined a t 230, 240, and 250 mp. Of 23 pesticides tested, only phenothiazine gave considerable interference. Niagara Chemical Division (76) has developed a method for determining Thiodan, utilizing the evolution of sulfur dioxide, and its reaction with basic fucsin to develop a colored compound. The absorbance is read a t 570 mp. The sensitivity is excellent but the method has not proved satisfactory for some types of samples, because of interfering materials which have not been successfully removed. Higgons and Toms (41) have reported a specific method for determining 2,3,5,6-tetrachloronitrobenzene (Technozone) and its isomers, based on methanolysis to the nitrite in boiling sodium methylate, followed by colorimetric determination of the nitrite. A spectrophotometric method for the determination of pentachloronitrobenzene was reported by Ackerman, Baltrush, Berges, Brookover, and Brown ( I ) . The compound is hydrolyzed and the liberated nitrite is used to diazotize procaine hydrochloride. Coupling with 1-naphthylamine produces a colored solution with a n absorption maximum a t 525 mp. Cleanup procedures for various crops are given. The determination of Perthane residues was discussed by Miles (69). The method of Fairing and Warrington, for methoxychlor, with slight modification, was found suitable for Perthane. Residues of 5 y could be detected in a 25-m1. aliquot of asparagus extract. On peas and corn, 0.1 pap.m. could be determined satisfactorily. A colorimetric procedure for determining endrin, described by Bann, Lau, Potter, Johnson, O’Donnell, and Weiss (4, is based on the formation of a colored complex using the phenyl azide reagent employed in the aldrin and dieldrin methods, and coupling with sulfanilic acid. Details of cleanup procedures are given for various crops and these will require modification in many instances. The method is extremely sensitive, but tedious and subject to many interferences which may lead to unduly high check and blank values. Brokke, Kiigemagi, and Terriere (13) have developed a colorimetric method for determining Aramite residues, based on hydrolysis with alkali to produce ethylene oxide. The oxide is trapped in acid medium and converted to formaldehyde with potassium periodate.
The formaldehyde reacts with phenylhydrazine and sulfuric acid to yield a brilliant red compound with an absorbance maximum at 520 mp. The sensitivity is 10 y or less, and the method is comparatively free from interferences. ORGANIC PHOSPHORUS COMPOUNDS
Xenn, Erwin, and Gordon (66) investigated the color reaction of several thiophosphate insecticides nhen paper chromatograms n ere sprayed LTith 2,6dibromo-N-chloro-p-quinoneimine. The spots ranged from yellow to bron n and as little as 1 y could be detected. Gehauf, Epstein, Wilson, Witten, Sass, Bauer, and Rueggeberg (33) have reported a method for the colorimetric estimation of some phosphorus conipounds using the acceleration of the osidation of amine bases, such as benzidine, as the basis for the method. The absorbances were read in a Klett colorimeter, using a No. 42 filter. Sensitivities were as low as 2 y for tetraethyl pyrophosphate and 10 y for parathion. The procedure is very rapid and accurate and, while developed primarily for nerve gases, may be applicable to many compounds in use as pesticides. A sensitive test for orthophosphate reported by Robinson and West (81) employs o-dianisidine molybdate as a reagent. The presence of orthophosphate results in a brown color. Addition of hydrazine hydrate gives a blue color. The method is sensitive to 0.05 y and is specific for orthophosphate. The only serious interference is the sulfide ion, which gives a blue color in both steps. These are spot plate tests, but may be adaptable to quantitative colorimetric procedures. The same reagent was used by Welch and West (98) to detect as little as 0.2 y of combined phosphorus. Oxidation with sulfuric acid was used to remove organic matter prior to analysis, but only a limited amount can be thus destroyed. Compounds containing only P-0 or P-S linkages showed excellent sensitivity regardless of their volatility. C-P bonds were less reactive and volatility became a factor. Two other methods are outlined nhich may be of value but are not as generally applicable or as sensitive as the first. Sass, Ludeman, Witten, Fisher, Sisti, and hliller (87) have reported a colorimetric method using a diisonitrosoacetone reagent for determining organophosphorus compounds. The reagent is added, followed by a buffer, and the absorbance is read after 7 minutes, a t 486 or 580 mp. A sensitivity to 1 y or less is claimed. Iron interferes but can be removed with a sequestering agent. The rapidity and simplicity of the method are exceptional. A method for determining malathion
residues in animal products was presented by Norris, Easter, Fuller, and Kuchar (77). The procedure is a modification of the method used for fruits and vegetables and the sensitivity is about the same. Versene was effeotive in eliminating interference dues to trace amounts of metals. Conroy (16) reported upon the use of the AverellNorris malathion method, slightly modified. Recoveries of the insecticide were improved by extracting with alcohol, diluting with water, and re-extracting into carbon tetrachloride, rather than extracting directly with the latter solvent. Dunn (SO) has developed a method for determining Delnav. The compound is converted to glyoxal by a cleavage reaction peculiar to acetals. The carbonyl compound may be determined either gravimetrically or colorimetrically as the 2,4-dinitrophenylosazone. Cleanup procedures are somewhat tedious and are discussed in detail. Absorbance is measured a t 614 mp in the colorimetric procedure and 10 y or less can be detected. Fournier (32) has reported a microcolorimetric method for determining tetraethyl pyrophosphate, in which the compound is saponified and oxidized with ammonium persulfate. The inorganic phosphorus is then determined by adding ammonium molybdate and stannous chloride in acid solution, and measuring the absorbance of the resulting colored compound a t 640 mp. The method is applicable to organic phosphorus compounds in general and might prove useful for residue determinations in some instances. A polarographic method for determining 0,O-dimethyl 2,2,2-trichloro1-hydroxyethyl phosphate (Bayer L 13/59) was reported by Giang and Caswell ($4). The procedure is useful for formulations and technical products, and has a minimum sensitivity of about 4 mg. per 100 ml. The accuracy is to =k2% of the amount present. Chloral hydrate and DDVP do not interfere. PYRETHRUM AND ALLETHRIN
Brown, Hollenshead, Phipers, and Wood (14, 15) have investigated the behavior of pyrethrins on alumina columns. Pyrethrum extracts could be analyzed by passing through the columns in a mixture of ether and petroleum ether. False pyrethrins m-ereseparated from the active components and pyrethrins I and 11, and cinerins I and I1 were separated by displacement. Quayle (79) successfully separated pyrethrins by paper chromatography, using untreated paper, n-ith an ascending solvent of light petroleum saturated with methanol. It was found that the partition coefficients of the pyrethrins are very much in favor of the less polar
of the more common liquid-liquid systems. Kelsey (60) has studied a method for determining allethrin based on the quantitative reaction of the compound with ethylenediamine to form chrysanthemum monocarboxylic acid. The acid is determined by titration with sodium methylate in pyridine. Chrysanthemum monocarboxylic acid, anhydride, and acid chloride interfere quantitatively and are determined independently. A reaction temperature of 25" 5 2" Fvas selected as the most suitable. Levy and Usubillaga (67) have applied the Levy-Estrada colorimetric method for pyrethrins, to allethrin in kerosine solution. Allethrin could be used as a standard of analysis for pyrethrins by this method, because the ratio of absorbance for pyrethrins and allethrin was a constant a t 1.71. Allethrin residues in meat and milk were determined by McClellan and Moore (6W),using a magnesium oxidesulfuric acid reagent to produce a red color. The absorbance was determined in a Klett photometer using a No. 47 filter. The use of a spectrophotometer might improve the accuracy and sensitivity. Samples were extracted with petroleum ether and the analyses were made with no purification. No interferences were noted. FUMIGANTS
Mapes and Shrader (65) have reported a method for determining total and inorganic bromide residues in fumigated products. Bromides were hydrolyzed with ethanolamine and evaporated to dryness. The residue was ashed with sodium hydroxide and sodium peroxide, and the bromide was leached from the ash and determined by the Kolthoff-Yutzy-van der Meulen method. The inorganic bromide was calculated as the difference between total bromide and volatile bromide. Ethylene dibromide was determined by Kennett and Huelin (51) by steamdistilling the sample and extracting the distillate with benzene. The bromide was decomposed with sodium hydroxide in a benzene-alcohol solution, and the liberated bromide was oxidized to bromate and determined iodometrically. A special reflux head was used to extract the ethylene dibromide from the condensate before it was returned to the flask. Desbaumes and Deshusses (28) determined methyl bromide in foodstuffs by heating the food t o 70" with an infrared lamp and carrying the methyl bromide, with an air current, into a quartz combustion tube a t 1000". Perchloroethylene was determined colorimetrically by Brumbaugh and Stnllard ( 1 7 ) . The sample v a s re-
fluxed in acid solution, the fumigant was swept into pyridine absorbers, aniline was added, and the solution was refluxed. Upon addition of sodium hydroxide, followed by methanol, a n intense color was formed. The method is very sensitive. A colorimetric method for ethylene oxide was devised by Critchfield and Johnson (27), based upon hydrolysis of the fumigant to ethylene glycol. The glycol reacted with potassium periodate to liberate formaldehyde, nhich was determined by reaction with sodium chromotropate to give a colored compound. Absorbance was read a t 570 mp and the sensitivity of the method was about 20 y, Dunning (31)has developed a method for determining carbon disulfide based on the reaction with Viles' reagent after liberation from grain by digesting with 1 to 1 hydrochloric acid. Sulfides were removed with a lead acetate trap. The range of the method was from about 1 to 250 p.p.m. Absorbance of the colored solution was determined a t 425 mp, Ramsey (80) has reported a method for the colorimetric determination of carbon tetrachloride. The sample was refluxed in acidified water under a hot condenser, and the fumigant was absorbed in acetone, and determined by the Fujiwara reaction. Absorbance was read a t 530 mp, and the sensitivity was to about 1 p.p.m. Two methods were reported for determining phosgene. Lambouraux (53) added an ethyl alcohol solution of 4(4-nitrobenzyl) pyridine to a n ether solution of phosgene to precipitate a compound, soluble in water, which produced a red color upon addition of alkali. Liddell (69) prepared a detector paper by dipping in a solution of alcohol containing N-ethyl-N-(2-hydroxyethyl) aniline, p-dimethylaminobenzaldehyde, and diethyl phthalate. A blue color was produced when 500 ml. of air, containing 1 y of phosgene, were drawn over it. HERBICIDES
Anglin and Mahon ( 2 ) determined residues of maleic hydrazide by steamdistilling with sodium hydroxide, zinc, and water. The hydrazine is collected in p-dimethylaminobenzaldehyde reagent to form a red product. Interfering materials from plant products Lvere corrected for by reading the absorbance a t 455 and 500 mp. Lane, Gullstrom, and Kewell (66) used a similar procedure, modified by adding ferric chloride to the mixture before distilling. Absorbances were read a t 430, 460, and 490 mp, and the residue was calculated by the base-line technique. A method for determining Alanap was also reported. This was a modification of the earlier method, and employed sulfanilic acid in 30% acetic acid as the coupling VOL. 31, NO. 4, APRIL 1959
727
reagent. A sensitivity of 0.1 p.p.m. is claimed. Green and Feinstein (5%) have developed a method for determining 3amino-l,2,4-triazole, consisting of diazotization, followed by coupling with chromotropic acid. The absorbance of the resulting colored compound was read a t 525 mp. The sensitivity is claimed t o be 10 y. On paper chromatograms, using the same reagents, 0.2 y can be detected. Smith, Getzendaner, and Kutschinski (90) have reported a method for determining Dalapon in sugar cane. The herbicide is hydrolyzed to pyruvic acid and converted to its 2,4-dinitrophenyl hydrazone. The absorbance of the colored hydrazone was read a t 440 mp, and a sensitivity of about 0.2 p.p.m. was achieved. Interferences were removed by putting the solution through a column. Carbonyl compounds were converted to the hydrazones, absorbed on the column, and removed. Amino acids, etc., were hydrolyzed to carbonyls and removed by treatment with copper sulfate and calcium hydroxide to form insoluble copper complexes. FUNGICIDES
Taylor and Klayder (98) reported a modification of the Kittleson method for determining Captan residues. A cleanup was devised to remove interfering materials and the residue was fused with resorcinol to form a red color. Addition of acetic acid gave a yellow color for which the absorbance was read a t 425 mp. A somewhat similar method was used by Wagner, Wallace, and Lawrence (96). The residue was fused with alkaline resorcinol under reducing conditions, and the absorbance of the resulting yellow color was read a t 447 and 500 mp. The reading a t 500 mp is that of the blank, and the difference between the two readings is taken as the absorbance due to the Captan. A microdetermination for Phygon in water was developed by Newell, Mazaika, and Cook (76). The Phygon was distilled after filtration of the water and acidification with phosphoric acid. The filtrate was extracted with chloroform and reduced to a small volume, and the absorbance was read a t 253.8, 259, 283.5, and 298 mp. The base-line technique was used for calculating the amount present, thus minimizing the effect of interfering compounds. Lane (66) used a method based on the reaction of Phygon with dimethylamine to produce a n orange color. This method proved to be sensitive t o about 1 y per ml. Bornmann (10) has reported a similar method, using benzene strip solutions which were reacted with dimethylamine in isopropyl alcohol. 728
ANALYTICAL CHEMISTRY
Spergon residues on crops were determined by Lane (64) by oxidizing diphenyl-p-phenylenediamine with .the fungicide to form the blue Wurster salt. The salt was extracted from the benzene reaction medium with an aqueous acetic acid-hydrochloric acid solution and the absorbance was read a t 700 mp. Where preliminary cleanup mas necessary, a mixture of sodium sulfate, Attaclay, and Filter-Cel in a 2:2:1 ratio by weight was suggested. A sensitive colorimetric method for determining 2,4-dichloro-6-(o-chloroaniline)-S-triazine and related compounds was developed by Burchfield and Storrs (21). The compounds reacted with pyridine and were made alkaline to form colored Schiff bases. Heurmann (40)has reported a method for determining residues of dialkyl dithiocarbamates based on heating in acid medium to form secondary amines which were distilled from alkaline medium. The amines were isolated and the colored cupric salt was formed for colorimetric determination. Barr, Clark, and Jacks (6) used a similar method for determining tetramethylthiuram disulfide and dimethyldithiocarbamate on apples. Pease (78) has determined dithiocarbamate fungicide residues, utilizing the carbon disulfide evolution method and a modified apparatus designed to ensure complete transfer of the carbon disulfide into Viles’ reagent. The method was proved for Ferbam, Ziram, Thiram, Zineb, and Maneb, on a variety of crops. Keppel and Munsey (62) employed a similar method, using a modified Viles’ reagent. Karathane was determined in food crops and animal tissues by Rosenthal, Gordon, Stanley, and Perlman (83) by a colorimetric method. The fungicide was separated by steam distillation, which includes any free dinitrophenol. Reaction with pyridine-water resulted in a colored compound for which the absorbance was determined a t 442 mp. Sensitivity, using a 200-gram sample, was to about 0.05 p.p.m. A special apparatus for steam distillation \?as described. Schiffman (88) has reported a method for determining sodium o-phenylphenate residues by steam distillation, extraction of the alkaline distillate with petroleum ether to remove oils, and reaction with 4-aminoantipyrine to form a colored complex. Absorbance was measured a t 510 mp. The method was used on apples, pears, and citrus fruits. MISCELLANEOUS
A colorimetric method for determining residues of Sevin (1-naphthyl N-methylcarbamate) has been developed by Union Carbide Chemicals Corp. (96). A procedure was outlined for the sepa-
ration of residues from interfering materials and determination of Sevin and 1-naphthol separately by reaction with p-nitrobenzenefluoroborate to form an intense blue color. The method is very sensitive (0.1 p.p.m. or better) and has the advantage of permitting independent determination of any 1-naphthol that may be present. Moorefield and Tefft (74) have utilized the cholinesterase-inhibiting property of Sevin for its determination. Using fly brain cholinesterase in a manometric procedure, a sensitivity to 0.05 p.p.m. was achieved. Human blood serum and red blood cell cholinesterase were also used, but Sevin was about 10 times more effective in inhibitor of fly brain cholinesterase than it was for that from human blood. Mitchell (70) has reported a paper chromatographic method for the detection of 2,3,4,5-bis (Az-butylene) tetrahydrofurfural (Repellant R-1 l), its alcohol, and its acid. An immobile solvent consisting of dimethylformamide in ether, and a mobile solvent of mixed octanes, were used. The sensitivity lvas to 1 to 4 y. Toren, Goodhue, Kirkham, and Howell (94) have developed a colorimetric method for this repellant, in milk. The repellant was separated by partitioning, reacted with 2,4-dinitrophenylhydrazine, and the absorbance was read a t 338 mp. A sensitivity of 0.1 p.p.m. was attained. Cyclethrin was determined colorimetrically by Sweeney and Williams (92) by reaction with orthophosphoric acid to produce a red color with an absorbance maximum a t 454 to 550 mp. Cyclethrin can be distinguished from pyrethrins by the time of heating required to produce the red color. Synergists interfere but may be removed by a silicic acid-Celite 545 column. hIenzie (67) has suggested a colorimetric method for m-dinitrophenyl pesticides. The method is specific for the m-dinitro structure and is based upon the reaction of hydrogen cyanide to produce highly colored compounds with a n absorbance maximum a t 350 mp. Bruce, Howard, and Zink (16) have presented a method for determining diphenylamine residues on apples. The amine is extracted into concentrated hydrochloric acid as the hydrochloride, diluted with water t o give the free amine, and extracted into petroleum ether. Reaction with diazotized 2,4dinitroaniline in acetonitrile, followed by addition of phosphoric acid, gives a colored complex with an absorbance maximum a t 530 mp. The aniline can also be determined directly in nheptane, in the ultraviolet region, a t 265, 282, and 300 mp. Baxter (6) has reported a rapid procedure for determining diphenyl in citrus. The sample is extracted with
n-heptane, and the diphenyl is oxidized with a n acid-potassium permanganate mixture and neutralized, and the absorbance is read at 248 mp. Hornstein (44) has investigated the use of the spectrofluorometer for determining pesticides. A considerable number of these compounds were studied and the results were discussed. A sensitivity as low as 0.01 y per ml. was attained in some instances; the procedure might prove useful and further study is warranted. The nematocide 3,4-dichlorotetrahydrothiophene 1,l-dioxide was determined colorimetrically by Burchfield and Schuldt (19). Extraction from soil was 90 to 100% effective, using dichloromethane. Interferences were removed by adsorbing on a mixture of Norit A and Florid. Reaction with 60% pyridine in a boiling water bath, followed by the addition of sodium hydroxide, gave a colored compound with a n absorbance maximum at 454 mp. Mitchell (73) has reported a paper chromatographic procedure for the separation and identification of Antu, Pival, and JF’arfarin. The paper was impregnated with a 4% solution of dimethylacetamide in ether and developed with mixed octanes. Ultraviolet light ivas used to detect the spots. LITERATURE CITED
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