I
REVIEW OF
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W. E. WESTLAKE Entomology Research Branch, U. S. Department of Agriculture, Yakima, Wash.
not .intended that t'his biennial i,eview be a complete and comprehensive siin;ey of the literature, but, rather, that; i t be a selective and critical review. Publications from S o veiiiber 195-l through October 1956 are covered. The select.ion of contributions to be included is, necessarily, based upon the author's opinion, guided by personal experience \{.it'llmany of the procedures and by the opinions of other n-orliei,s in this field. The continued high level of interest in analytical methods for the deterniination of pesticides has been commented upon in previous reviews by St. John (76, 76). The enactment of Pulilic Law 516. coinmonly known as tlie Miller Aniendiiieiit, amending section 201 of the Federal Food, Drug, and Cosmetic Act,, has given added impetus to the developiiient of analytical methods, particularl\- micromethods, suitable for the determination of pesticide residues in agricultural products. Official tolerances ha\-e been established for the pesticides in general use and are being set for new materials a s rapidly as the required data on residues, toxicity, etc.. ca,n be obtained. It is n o r essential that :in acceptable analytical method for detemiir Ling residues be developed before registration can be obtained for tlie use of a n y nerv material. While nonspecific analytical met,liods have been accepted in many instances, it is highly desimble that specific methods be developed fcr each pest'icide. Much of the \.iork during the past 2 years has been concerr.ed with the development of such 111ct110ds. Khile nirtcromethods for pesticide determination are available through the Methods Clearinghouse of the Xssociation of Ahiierican Pesticide Control 0fici:ils. no such source is yet arailable for microinetahods necessary for residue det'erminations. Gunther and Blinn (56) hare presented an excellent survey of hoth macro- and niicromethods published t,hrough 1954. Frear (26). in the most recimt revision of his book, discussed tlie chemistry and analysis of pesticides. hut, unfortunately, included no literature references later than 1952. An excellent, discussion of the chemistry T IS
and structure of organic insecticides, with particular reference to their mode of action, was given by Metcalf (60). Virtually e r r r y micromethod, to be suitable for the determination of pesticide residues, must include procedures for removing interfering materials extracted with the pesticide. Only too often, the method for a given pesticide must be altered for different products being analyzed. Few, if any, of the known methods of analysis ~ d give l acceptable results, without some modification, under all conditions encountered in the study of residues. While the actual chemical analysis is of paramount importance to the chemist engaged in residue determination, i t is also of the utmost importance, if results are to be valid in all respects, that all phases of the experiment, including extraction of the sample to remove the pesticide, where necessary, sampling, application of the pesticide, etc., be carried out in a manner that will ensure that a n adequate sample reaches the analyst. The most precise chemical analysis is of little or no value if it is made on an inadequate sample. Perhaps the best available discussion of the entire problem of peticide residue determination, from the planning of the experiment to the actual analysis and the reporting thereof, is given by Gunther and Blinn (36). CHLORINATED HYDROCARBONS
General. A considerable number of pesticides are included in t h e general classification of chlorinated hydiocarbons. T h e chlorinated hydrocarbon pesticides h a r e been t h e subject of a great amount of investigation and excellent analytical methods have been published for many of them. The importance of proper cleanup proceduresprior to chemicalanalyeis cannot be overemphasized, and two papers are of particular interest in connection with this problem. Erwin, Schiller, and Hoskins (25) have discussed a reversed phase partition column consisting of alumina coated with m x , for removal of interfering extractives from plant or anininl tissues. O'Donnell et al.
(70) have described a detailed cleanup procedure for use in the determination of aldrin prior to analysis. With modifications, the method is applicable to many pesticides. Qualitative tests for a number of chlorinated hydrocarbons were given by Johnson (CY),who claims that the methods are simple and accurate enough for routine use in detecting the presence of these compounds. hlethods are given for chlordan, methoxychlor, toxaphene, D D D , D D T , heptachlor, aldrin, dieldrin, and endrin. Organic chlorine determinations are widely used in the analysis for chlorinated hydrocarbons and a n important contribution has bern made b y Phillips and DeBeiiedictis (12), r~ho have presented a siniple sodium reduction technique, followed by amperometric titration, for the microdetcimination of chlorine in organic chloridc>s. The sodium reduction method has bcen widely used, but previous techniques have lacked the sensitivity necessary for microdeterminatione. Sensitil ity and accuracy comparable to those 01)tained by combustion methods are possible with this procedure. Liggett (56) has suggesteda total chlorinemethod using sodium or lithium biphenyl for the decomposition of the chloriaated hydrocarbon pesticides. The method requires a very short reaction time. and should prove useful for control analyses in formulations and technical products. It is claimed to be accurate to about 2 parts in 100, and obviously lacks the sensitivity necessary for residue d e t n minations. I n a continuation of investigations of chromatographic procedures to separate and identify chlorinated hydrocarbons, lIitchell(64) has reported on the separation of mixtures of technical benzene hexachloride, lindane, technical D D T , and T D E (Rhothane). The procedure is designed for practical spray residue testing but has not been proved for this purpose. I n further work, hlitchell (6b)has described aprocedure forseparation and identification of Aramite, captan, dieldrin, lindane, chloranil (Spergon), and tritisan, in mixtures, b y paper chromatography. RI values are given. S n additional note (66) has VOL. 29, NO. 4, APRIL 1957
679
described a n improvenient ill sensitivity through the use of 2-phenoxyethanol as the immobile solvent. Sensitivity tests indicate a good positive reaction for 1 y or less of the compounds ieported upon in the previous paper. DDT. D D T has probably been t h e subject of more study t h a n any other pesticide, and several excellent niethods of analysis are known. Three recent procedures may be of interest t o analysts. A simplified method for determining D D T residues n a s described b y Amsden and Walbridge (9). Sitrated D D T reacts with isopropylamine to produce an intense yellou- color. It is claimed that traces of D D T may be estimated and that the method has the advantage of being adaptable for use with inadequate laboratory facilities. Martin and Batt (59) have reported a modification of the Schechter-Haller colorimetIic method for which they claim great sensitivity. A chromatographic procedure foi the separation of D D T and D D E mixtures was described by Amell and Helt (1). D D T is separated from DDE, using a silicic acid chromatographic column, with n-hexane, saturated with nitromethane, as the solvent. The method is claimed to be simple and accurate, and the compounds are recovered quantitatively Benzene Hexachloride. Klein (60) has reported on a collaborative study made in 1955, in 1% hich t h e SchechterHornsteinmethod gave satisfactory results in t h e hands of collaborators. T h e method was recommended for adoption for official use, although further studies of sample preparation and extraction were considered advisable. Hornstein (43) has developed a sulfonation purification procedure which permits the determination of lindane in mushrooms. The sulfonation procedure should prove generally applicable where direct analysis or simple extractions are inadequate. A revision of the Association of Official Agricultural Chemists’ partition chromatographic procedure for determining y-benzene hevachloride has been recommended by Hornstein ($4). The separation and determination of the isomers of benzene hexachloride have proved difficult, and no simple, direct procedure for routine use has been found. The tlvo most promising approaches have been the use of chromatography and polarography. Bridges, Harrison, and Winteringham (10) have reported a separation of the isomers of technical benzene hexachloride using reversedphase partition chromatography. R f values for the various isomers are given and it is claimed that 5 grams or less of the isomers can be detected. Fujii and coworkers (68) have described a polarographic method for the determination of y-benzene hexachloride which, it is claimed, gives 98 to 102% recoveries
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ANALYTICAL CHEMISTRY
with an error of ~ t 2 . 5 7 , . -4 polarographic method for the determination of the gamma isomer in cattle dips was developed by Kalker (81). K a t t (83) has described an impurity-compensated polaiographic method for the deteiniination of the gamma isomer in technical benzene heuachloride. It is claimed that the iesults shoJT excellent agreement u i t h those obtained by other methods and usually are within 5% of the c ~ i l e cvalue. t Dieldrin. T n o methods for the determination of dieldrin residues in crop materials, both of which 1 equiie eepaiation of the insecticide from plant niateiials b y extraction and chromatography, n ere reported by O’Donnell. Johnson, and Keiss (69). -4 spectiophotometric method involving reduction of the epoxide group to an olefinic group. followed by reaction with phenyl azide to form a colored product, was found to be more specific and sensitive than a method involving total chlorine determination, although both methods n ere pioved capable of determining as little as 0.1 p.p.m. The infrared spectrophotometric determination of dieldrin and D D T simultaneously in insecticidal dust mixtures was reported by Pollard. Saltman, and Yin (7.9). The method can also be applied to liquid formulations but is not intended for use in the determination of residues. Chlorobenzilate. Blinn, Gunther. and Kolbezen (7) have presented two analytical methods for the microdetermination of 2-hydroxy-2,2-bis(4-chlorophenyl) ethyl acetate (chlorobenzilate) in the presence of citrus extractives. The compound is hydrolyzed to p.p’dichlorobenzilic acid, which is oxidized to p.p’ - dichlorobenzophenone. The ketone may be determined spectrophotonietiically a t 264 mpJ or its dinitrophenylhydrazone may be determined a t 510 mp. A sensitivity of 15 y is claimed. .4 two-stage cleanup of accessory extractives is included. making the method very specific. A colorimetric method for determining residues of chlorobenzilate, described by Harris (39).involves nitration of the compound, followed by reaction of the nitrated product n i t h sodium methylate to produce a red color which is measured spectrophotometrically a t 538 mp. The method has been further developed to permit determination of the compound in the presence of D D T , by saponification of the chlorobenzilate to 4.4’-dichlorobenzilic acid, which is extracted from the dehydrochlorinated D D T and nitrated. Heptachlor and Chlordan. Ordas, Smith, and Meyer (71) have described modifications of t h e Davidow method for t h e determination of chlordan and the Polen-Silverman method for heptachlor. Microtechniques permitted detection of t h e toxicants in t h e 2.5- t o
.50-y range. Chromatography was used to separate as little as 2 y of toxicant, Ivith about 80% recovery from as much as 2 kg. of crop material. Good agreement with bioassays was observed and the method was tested on a large nunilier of crops. Toxaphene. Johnson ($5) has decribed a method for the deterniination of toxaphene in formulations, using a colorimetric procedure. T h e method, however, lacks the sensitivity required for detecting sniall amounts. Hornstein (4%’)has developed a colorimetric method of analysis for residues that promisee to be of value, particularly \\-here it is necessary to determine tosaphene in the presence of ot’lier clilorinated hydrocarbons. ORGANIC PHOSFHORUS COMPOUNDS
General. Cook (16) has presented a method for detect’ing. on paper chromatograms. sniall quantities of some organic phosphorus insecticides n.hich contain sulfur. Separation of seven technical organic thiophosphntes b y reversrd-phase paper chroniatopraphy was also reported by this author ( 1 7 ) . and R , values were cktei,mined. The effect of light on denieton isomers was also investigated and the isomers and b r e a k d o n products were isolated by means of paper chromatograms by Cook (18). I n another series of experiments, Cook (19) has developed a qualitative procedure permitting visual in vitro location of cholinesterase inhibitors on the chromatogram. A significant discovery was reported by Fallscheer and Cook (%’$),in which they used dilute bromine water to convert thionophosphates and a dithiophosphate to cholinesterase inhibitors. Vse of t’lie bromine treabment was suggcsted LIS a method for analysis of residue quantities of these compounds. A comparison was shown of parathion. paraoxon. Diazinon, malathion, Chlorthion. inethyl parat’hion, and EPN before and after treatment. Giang, Barthel. and Hall (SO) have presented a method for d&rmining 0,O-dialkyl-1-hydroxj-phosphonates derived from chloral. Chloid, condensed with dimethyl phosphite yields 0,O-dimethyl 2,2,2-tricliloi~c1-1hydroxyethylphosphonate (Dipteres). This, and other compounds of similar structure were quantitatively estimated by heating to split out chloroform which was absorbed in aqueous pyridine and warmed withalkali to develop a redcolor. The method was found to be seiisitive to 20 y of Dipterex. Parathion. Biffoli ( 5 ) has developed a procedure for t h e determination of parathion in olive oil. The method for separation of the parathion from the oil may be applicable to
other pesticides and to othei oily products where a separation is necessary before analysis. Demeton. Hensel, Hewitt, Sheets, and Scott (41) have developed a micromethod for determining demeton residues, based on t h e cholinesteraseinhibiting properties of t h e technical product. T h e method is very sensitive and, with proper extraction procedures, is applicable toan-ide variety of agricult~irnlproducts. It has the disadvantage of being nonspecific and mill detect any material that will inhibit the action of cholinesterase. Foi this same ienson, the method. with slight modification. niay be used foi other oiganie phosphorus pesticides. Nagee (56) has miployed chromatography to shou that the denleton studied was a mixture of organic pliosphoius compounds. Chromatography n as ful ther used to determine the residues 1 cniaining in plant materials after treatment with denicton. Bioassay was also used to indicate aniounts of the pesticide incorporated in growingplants. hletcalf. March, Fukuto, and l l a x o n (62) have presented an excellent discussion of analysis bj- the cholinesterase method and by radioassay todetermine denieton and its metabolites in plant materials. The last two publications are of particular interest, since they offer a n insight into the fate of the demeton after absorption by gi on ing plants. Schradan. Xletcalf, Fukuto, Reynolds, and March (61) ha\-e ieported t h e determination of octamethylpyrophosphoraniide (schradan) residues in cotton and cottonseed products b y radioassay, using iadioactive phosphorus-32. T h e material was completely nietabolized to acidic products in ground cottonseed meal and cake, demonstrating the value of radio tracer studies in determining the hehavior of systemic pesticides. Heath, Cleugh, Otter, and Park (40) have described a method for determining traces of schradan in agricultural products, involving microdistillation for separating the insecticide from the natural products in crop extracts. The technique should be generally applicable to the determination of residues of other pesticides of volatility similar to. 01 greater than, that of schradan. Blanks and recoveries are listed for various crop extracts. Chlorthion. Kolbezen and Barkley (51) have presented a method for the determination of residues of 0-(3-chloro4-nitrophenyl) 0.0-diniethylphosphorothioate (chlorthion) in milk. The method of A4verelland Norris. for parathion, mas used, with minor modifications. Concentrations greater than 0.1 p.p.m. in 500 ml. of milk may be determined spectrophotometrically, TI hile concentrations from 0.02 to 0.1 p.p.m. may be estimated by visual comparison. using hressler tubes. A method for the
determination of clilorthion in cottonseed was desciibed by Kolbezen and Reynolds (52). The procedure includes extraction. liquid-liquid partition, and chroniatography. It is claimed that the nietliod is sensitive to 0.02 p.p.ni. in 200 grams of cottonseed, spectrophotonietrically. and to 0.01 p.p.ni. by a visual eoniparative method. Diazinon. Harris (38) has described a spectrophotometiic method for t h e rleteirninatioii of iesidues of 0 , O - diethyl - 0 - ( 2 - isopropyl - 6methyl - 4 - pyriniidyl) thiophosphate (Diazinon). The method is specific but is subject to interference fioni plant extiactires. Blinn and Gunthex (6) have modified the niethod of Hariis for use in determining Diazinon residues in milk. The method includes f1 eezedrying the milk, extraction with petroleum ether. and partition of the pesticide into acetonitrile. An analytical procedure for determining Diazinon residues was suggested by Gigger (JS), based upon the methylene blue reaction of Chain. This method had the disadvantage of possibly not detecting some metabolic products wliich might occur, and Gigger (34) has developed a procedure, based on the determination of the sulfide group. n-hich is sufficiently sensitive foi residue determinations and which overcomes the objection to the methylene blue method. DDVP. Giang, Smith. and Hall (32) have reported a method foi the determination of residues of dimethyl 2,2-dicIilorovinyl phosphate (DDT'P) in various crops. The method is a modification of that used for denleton and other organic phosphorus conipounds, based on the inhibition of cholinesterase in vitro. Dimefox. DupBe, Heath, and Otter (22) have developed a method for determining iesidues of tetramethylphosphorodiamidic fluoride (Dimefox) in crops. Preliminary treatment, including microdistiIlation, is used to remove interfering materials. The conipound is then estimated as phosphate by the method of Berenblum and Chain. Guthion. Wollenberg and Schrader (85) have described a specific method for the determination of 0,O-dimethyl S-14oxo-benzotriazino-3-methyl) phosphorodithioate (Guthion). The compound is dissolved in glacial acetic acid, digested with phenyl-1-naphthylamine. acidified, and heated to de\-elop an intense blue-violet color, with an extinction maximum at 570 nip. Malathion. J u r a (48) has reported a polarographic method for determining technical grade S-(1,2-dicarbethoxyethy1)-0,O-dimethyl dithiophosphate (malathion). T h e method permits correction for t h e unreacted diethyl fumarate in t h e technical product.
PYRETHRUM A N D ALLETHRIN
B r o m and Phipei,s (13) Iin~-estudied the degradation of pyretlirins a n d coinpared analytical methods in fJ.xiiiiining the partially degraded riiatei~ids. Evidence of a tn-ofold attack 011 the pyrethrin niolecule by artificial irrndiation is given, as evidenced hy diffei.cwces in result's giyen by the Sei1 titi,inietric method and the Shukis (and otliei~s) spectrophotometric method. Brown, Phipers, and Kood (14) Iiavc dt~\x~loped a modification of the S-color test of I.cvy and Estrada which affords a rapid n i i ( ~ o method for the detcrmination of pyrethrum extracts and residues. I n further studies, Bronn. HollensliPad, Phipers, and JVood (12 ) have compared tlie mercury reduction and S-color iiiethods viith bioassays of pyrethrum extracts degraded 1)y irmdiation and found the S-color method to agree best \\-ith the biological method. Cornelius (20) has proposed a chromatographic procedure, using alumina :IS tlie adsorbent. followed hy spectrographic det,erniination of the cluates to determine pyrethrins in py'ethruni extracts. Moore (67) has developed n nietliod for the determination of pyrethrin and allethrin concentrates by forming the 2,4diiii t rophenylhydrazones which were chromatographed on :iluxnina ; the eluates were determined specti~opliotonietrically. Green and Schechter (35) have also described a method for determining allethrin based on the formation of the 2,4-dinitroplieiiylli~drazoiie,which was chromatographed on a silicic acid column, and a gravinietric or colorimetric determination made on the niaiii band. The method is not as precise as the ethylenediamine method hut should he useful as a check on other methods. Wlliams, Dale, and Sn-eeney (84)h ~ r - cproposed a colorimetric method for the deterniination of pyrethrins. based on the red color produced n-hen pyrethrins are heated with a reagent consisting of 80% orthophosphoric acid and 20'3 ethyl acetate. This test appears to be specific and piperonyl hutoxide. \T-hich suppresses the pyrethrin color. can be separated by chromatography. .;in infrared spectrophotometric method for the determination of allethrin has h e n developed by Freeman (e?'). PYRETHRUM SYNERGISTS
Beroza (4)has applied the chromotropic-sulfuric acid method for the determination of methylenedioy-l gi oups to the determination of pyrethrum syniiergists containing these groups. The method was applied to the estimation of piperonyl butoxide. sulfoxide, piperonyl cyclonene, and n-propyl isonie, in fly sprays. It may also be applicable to the determination of synergists in aerosol formulations, although means of elimiVOL. 29,
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natiiig interferences by some of the more important constituents must be noilied out. Beroza (3) has found that insecticide synergists containing the 3,4methylenedioxyphenyl group can be identified in the 2- to 10-7 range b y chromatography on paper strips impregnated with paraffin oil, with 30% acetic acid as the developing solution. A procedure for direct determination of the position of the compound on the strip, by spectrophotometry, was developed. The method has the advantage of reducing interferences from other materials usually present in insecticide formulations. Blum (8) has developed a n analytical method for determining pyrethrum synergists based on the formation of colored complexes in the presence of gallic and sulfuric acids. The color formed was found to follow Beer’s lan. in the 5- to 80-7 range. HERBICIDES
The tremendous increase in the use of herbicides, largely as the result of the development of many new hormone-type coiiipoiiiids for this purpose, has focused attention on the need for methods of analysis, particularly those suitable for determining residues in plant materials. The number of papers appearing in the literature during the past 2 years probably does not indicate the amount of work actually under way. A micromethod that will determine as little as 5 y of 2,4-dichlorophenoxyacetic acid in a 200-gram sample of grain or seed has been reported by Marquardt and Luce (58). A procedure for chroniatographic separation to remove interfering plant materials is folloxed by reaction v i t h chromotropic acid in sulfuric acid to produce a colored compound which can be measured spectrophotometrically. Sorensen (79) has proposed specific methods for the deterniination of 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, and 2-methyl-4-chlorophenoxyacetic acid in technical mixtures. by dilution analysis. The method may prove of value in the analysis of mixtures sometimes employed as herbicides. Bokarev and Mel’nikov (9)and Shebuev, Peshekhonova, Kirilenko and Kurcheninova (78) have developed methods for the analysis of 2,4 - dichloro - phenoxyacetic acid preparations. Langston (54) has used a radioactive tracer technique to investigate the absorption of bis(ethy1 xanthic) disulfide (Herbisan or Sulfasan) in plant tissues. The procedure is of no value for routine residue determinations but affords valuable information on the uptake of the material b y plants under various conditions. A colorimetric method for determining 3-amino-1,2,4-triazole in soils was developed by Sund (80). The method wvns used primarily for the determina-
682
ANALYTICAL CHEMISTRY
tion of residues in soils, and evidence is given to indicate that the uptake of the herbicide by plants is proportional to the amount recoverable from the soil. Sen and Leopold (77) have described the behavior of a number of indole derivatives, including a number of plant gron-th regulators, upon paper chromatography in several solvent systems. Gard, Pray, and Rudd (29) have reported a colorimetric method for the determination of residues of isopropyl A7-(3-chlorophenyl) carbamate in food crops. The method involves hydrolysis of the herbicide to 3-chloroaniline, with sulfuric acid, and colorimetric estiniation of the 3-chloroaniline. Sensitivity to about 0.05 p.p.m. is claimed.
farin was discussed and results of a collaborative study were presented. The method has been recommended for adoption as official. Nebbia (68) has developed a spectrophotometric method for the determination of 3-(a-acetonylbenzyl)-4-hydroxycoumarin in commercial preparations. BIOASSAY
Bioassay procedures, although they cannot be classed as chemical analyses, have an important place in the analysis of pesticides and deserve some mention in a review of this type. Bioassay must frequently be resorted to in determining pesticides for which no chemical niethods have been developed, and it also has a very important use in checking FUNGICIDES chemical methods. Burchfield and Hartzell (15) have deKeppel (49) has developed a coloriveloped a new bioassay procedure based metric method for the determination on the photomigration of mosquito of residues of tetramethylthiuram disullarvae as affected by pesticide concenfide (TMTD) in corn samples. The trations. The method has the advanmethod should be applicable to other tage of giving results in a few houis. cereals. Dithiocarbamates may intercompared with 24 to 48 hours requiied fere to some extent but may be disby former methods. Extreme sensitinguished from the tetramethylthiuram tivity is reported for many pesticides. disulfide by the ultraviolet absorption Another new and interesting developcurve. An infrared method, utilizing ment is reported by Michael, Thompson. the potassium bromide pressed disk and Abramovitz (63) who used brine technique, for determination of tetrashrimp (Artemia salina) as the test ormethylthiuram disulfide, was presented ganism for the detection of insecticide by Firestone and Vollmer (25). The residues. The brine shrimp has the admethod is primarily useful for analysis vantage of being readily available and of formulations, and correction for extremely easy to rear. Furthermoic. pesticides other than dithiocarbamates i t is very sensitive to many pesticides. may be made by use of absorption bands Prescott, Emexson, and Ford (74) beyond 12 microns. have reported a bioassay procedure ,Johnson (46) has described a coloriusing S. pastorianzts, to determine resimetric procedure for the determination of 2,3,5,6-tetrachloro-l,4-benzoquinone dues of cycloheximide (8cti-dione) in cherries. Amounts as low as 0.04 p.p.m. (chloranil) in fungicide formulations. could be detected in the fruit. The chloranil is converted to chloranilic acid, which is determined spectrophotometrically a t 545 mp. MISCELLANEOUS Mapes and Shrader (57) have pre\Tatson (82) has described a niethotl sented a method for the determination for the determination of 2-(p-tert-butylof perchloroethylene in strawberries inphenoxy)-1-methylethyl 2-chloroethyl volving the extraction of the fruit with sulfite (Aramite) residues based on the diethyl ether, and determination of liberation of sulfur dioxide. -4s little chloride by a nephelometric method. as 2 y of Aramite can be detected, with Sensitivity to about 1 p.p.ni. is indian error not exceeding 2.5 y, in the 5cated. Deshusses and Desbaumes (21) to 30-7 range, i t is claimed. -4method have offered a n alternative method for for the determination of Aramite involvperchloroethylene determination involving hydrolysis, oxidation of the ethylene ing removal of the fungicide by a n air evolved to formaldehyde, and detercurrent, decomposition a t high temmination of this compound colorimetriperature, and titration of the resulting cally, was reported by Brokke, Kiigehydrochloric acid with silver nitrate. magi, and Terriere (11). This method is a modification of that developed by RODENTICIDES Gunther and others, and overcomes some of the difficulties experienced by LaClair (53) has reported on the other workers attempting to use the ultraviolet spectrophotometric determethod. mination of 2-pivalyl-l,3-indandione Giang and Smith (31) have described (Pival). Some difficulty was experia colorimetric method for the deterenced in determining the Pival, due to mination of metaldehyde residues on lo^ results, and further study was recplants. The method is claimed t o be ommended. A spectrophotometric sensitive to 0.05 y of metaldehyde. and method for the determination of war-
ir,siducs n e i e dcteiniined on scvcinl 1Jnnt s. A method fox the deterniinatioii of the total thiocyanate coiitrnt of insecticides, employing infrared spectroscopy, was I t,ported by Hannan (87‘). The infra1 ed spectra of three typical insecticide thiocyanates. Lethane 384, Lethane 60, and Thaiiite. ale shonn. LITERATURE CITED
(1) hmell, -1 R , Helt, R., J .lgr. Food Chem. 3, 53 (1955). (2) hmsden, R. C., Walbridge, 11. J., Ibzd., 2, 1323 (1954). (3) Beroza. RIorton. ANAL. CHEW 28.
1550’(1956). ‘ Beroza, Morton, J . $ g r . Food Chem. 4,53 (1956). Biffoli, Roberto, Boll. lab. chim. provinciali (Bologna) 6, 21 (1955). Blinn, R. C., Gunther, F. A., J . ,4gr. Food Chem. 3, 1013 (1955). Blinn, R. C., Gunther, F. A., Kolbezen, J. AI., Ibid., 2 , 1080 (1954). Blum, RI. S., Ibid., 3 , 122 (1955). Boltnrev, I
