ANALYTICAL CHEMISTRY
108 complexes depends to a different extent upon the concentration of the hydrogen ion, there opens up the possibility of the parallel colorimetric determination of the complexes by means of properly adjusted p H values. On changing the initial ferric ion concentration and the dimensions of the cuvette, the amount of the ions to be determined may vary widely.
D”.
i
f L ’
25
PH
Figure 7.
-
75
5 16
-mg
i0
SCN-
Effect of Thiocyanate
On % transmittance of ferric-oxalate (-) and ferric-citrate (-.-.-.) systems a t pH 1.6 Volume of reagent. 5 ml. of ferric thiocyanate, 25 ml. of citrate, 10 ml. of oxalate
Figure 6.
Calibration Curves of Oxalic, Tartaric, and Citric Acids
-
Effect of oxalic (-), tartaric (- -), a n d citric (-----) acids on 70 transmittance of ferric-thiocyanate systems a t pH 1.6
Another q-ay of extending the limits of the measurements is the changing of the thiocyanate concentration. This can be seen from the data demonstrated in Figure 6. CONCLUSION
The circumstance that the decrease of the extinction of the different complexes varies to a great extent with the pH enables the different ions to be determined independently, which is particularly significant in the case of certain organic acids.
I n the literature the determination of the stability constants of the complexes is gaining more prominence ( 2 ) . The preconditions for their analytical application are discussed above. ACKNOWLEDGMENT
Thanks are due to S. Iisldor for his hclpful assist.ance in the extinction measurements. LITERATURE CITED
(1) Beck, >I.,and Seab6, Z. G., Anal. Chim. A c t a , 6, 316 3,1952). (2) Chem. Eng. News, 29, 40T8 (1951). (3) Hein, Fr., “Chemische Koordinationslehre,” p. 229. Leipzig,
Hirzel Verlag, 1950. (4) Ingols, R. S., et al., AXAI..CHEM.,22, 799 (1933). ( 5 ) Lacroix, S., A n d . Chi7n. A c t a , 1, 3 (1947). RECEIVED for review F e b r u a r y 4, 1952. .4coepted September 13. 1952.
Detection and Determination of Thallium J. R. -4. ANDERSON New South Wales University of Technology, Sydney, Australia
T
HE element thallium was discovered by Crookes in 1861. It is one of the rarer metals and occurs in small amounts in the minerals crookesite, lorandite, hutchinsonite, and vrbaite. It also exists in very small quantities in sea water and in certain mineral waters, and is widely distributed throughout the vegetable kingdom, being found in traces in wine, chicory, tobacco, beet, and beechwood. I t s chief industrial source is in the chamber mud from sulfuric acid plants in which thalliferous pyrites are burnt, and in the flue dusts of blast furnaces and zinc refineries. Alloys of thallium have many industrial applications and soluble thallium salts, on account of their extreme toxicity, are finding increasing use as economic poisons for the extermination of rodents and other pests.
DETECTION OF THALLIUM
Because of its toxicity it is often necessary to detect minute amounts of thallium, This is best done ~pectrographically, but wet methods or sensitive microchemical tests may be eniployed. Thallium gives a broad green line a t wave length 5350.7 A. and is, therefore, readily detected by means of the spectroscope. De l l e n t and Dake (16) report that univalent thallium salts form a double salt with uranyl carbonate, which emits fluorescent radiation in the short-wave region of the visible spectrum. The fluorescence detection of thallium was carried out by Got; (@), who found that thallium(1) was like silver in preventing the fluorescence of uranyl sulfate solution. Thallium(III), however, changes the fluorescence of rhodamine
V O L U M E 2 5 , N O . 1, J A N U A R Y 1 9 5 3
109
The analytical chemistry of thallium covering methods disclosed in the literature mainly over the period of 1940 to 1950 is reviewed. The detection of thallium by spectrographic, fluorescence,- and micromethods is described. The quantitative determination of thallium by many gravimetric methods and the use of the thermobalance for the gravimetric estimation of various compounds of thallium are dealt with. The volumetric determination of thallous salts by oxidation methods is discussed, while the application of spectrography, polarography, radioactivity, and chromatography to the determination of thallium, and methods for its potentiometric, conductometric, and electrolytic estimation also receive some attention.
R from red to violet, as little as 0.5 microgram giving the test. The fluorescence of cochineal in aIkaline solution is destroyed by 0.5 microgram of thallium(II1). According to Sill and Peterson (48), thallium(1) compounds in a 4-inch depth of saturated sodium chloride solution show a bright blue fluorescence a t a dilution of 1 part in 50,000,000-hen illuminated from above g i t h mercury radiation of xave length 2537 A. Thallous salts are more stable than thallic salts and hence are of greater importance from the analytical point of view. I n recent years many reagents have been advocated for the detection of thallium. Among these may be mentioned benzidine, dipicrylamine, potassium iodide, sodium carbonate, and a mixture of phosphomolybdic and hydrobromic acids, all of which were introduced as spot reactions by Feigl and coworkers (90). Wclcher (59) mentions many organic reagents for the detection of thallium, including: acetoacetic acid ethyl ester, acetylacetone, dibenzoylmethane, ethyl acetopyruvate, benzoylacetone, benzoyl pyroraceniic acid ester, methyl benzoylacetone, and oxalacetic acid ethyl ester, all of which give yellow derivatives with thallous salts. Gallic acid, tannic acid, benzoic acid, tartaric acid, pyridinc, saccharine, uric acid, thiocarbonates. o-tolidine, sozoiodol. phenanthrene quinone nionoxime, mercaptobenzothiazole, alizarinsulfonic acid, styphnic acid, thiourea, and thionalide have also been reported as reagents for the detection of thallium. Recently it has been shown (1) that in the absence of interfering ions, as little as IO+ gram of thallous ion may be detected by means of alkyl xanthates and that 1 part of thallous ion in 20,000 parts of solution can be detected by microscopical examination of the yellow crystals which are formed with picrolonic acid. A new and sensitive microtest for thallium has recently been reported by Jurany ( 2 7 ) , in which a characteristic red precipitate is formed when sodium iodide and cesium chloride are added to a thallic salt. As little as 0.06 microgram of thallium can be detected. QUANTITATIVE ESTI3lATION OF THALLIUM
Gravimetric Determination. Xany methods are described in 51-hich thallium is precipitated as the chromate (S?), cobaltinit,rite (5S), metal (45),and iodide (31). More recently the following methods have been introduced: .4s THE THIONALIDE COvPouND. Because thallium alone is precipitated by thionalide (thioglycollic 8-aminonaphthalide) in a solution containing sodium hydroxide, sodium tartrate, and potassium cyanide, this substance has been recommended by Berg and Fahrenkanip ( 5 ) for its estimation. The yellow complex formed is washed n.ith cold water, then with acetone, and dried at 100" C. It contains 48.60% thallium. As IXNERCOMPLEX S.~LTS.According to Feigl (19), trivalent thallium forms inner complex salts with nitrosophenylhydroxylamine, 1-nitrosonaphthylhydroxylamine,8-quinolinol, 5,i-dibromo-8-quinolinol, and N-2-naphthylthiogl ycolamide. As THE THIOUREA COMPOVND.A4method is described by Mahr and Ohle (32) by which it is possible to separate thallium from most other ions by means of thiourea in a solution containing perchloric acid.
-15
I I L R L LPTOBCYZOTHI k Z 0 1 E
(OR
2-fihlZOTHIAZOLETHIOL)
COMPOCNUThis reagent was introduced by Spacu and Iiuras (61) for the determination of thalliuni, a yellow precipitate being f0rmc.d 11 ith thallous salts. .4s THILLOUS CHROVATE.The method of Moser and Biukl ( 8 7 ) for determining univalent thallium as the chromate has been adapted by Forchheimer and Epple ( 2 1 ) to perchloric acid solutions. BY kfE4NS O F THE THERMOB~LANCE. Using thionalide R S reagent, Umemura (57) states that the proper heating temprrature of the thallium thionalide coiiipound is less than 220" C. More recently, Peltier and Duval (41) have shown, with the aid of the Chevenard thermobalance, the following limits for drying or igniting thallium derivatives, before neighing them: TI208 (prepared chemically), 126" to 230" C., T1,01 (prepared electiolytically), 156' to 283" C.; thallium chloride, 56" t o 425' C.; thallium iodide, 70' to 473' C ; thallium sulfate, 92" to 355" C.; luteocobaltic thallium chloride, T I C ~ ~ . C O ( ~ %50" )~t , o 210" c.; T12Cr04,97" to 745' C.; TIzPtC16, 65' to 155' c.; thionalide complex, 69' t o 156" C. ; mercaptobenzothiaaole complex, ,52" to 217" C. The thiostannate and hexanitrocobaltate n r r e not considered suitable for quantitative work by these expc'iiinenters hlso, according to them, both the chemically prepared and the electrolytic TI2O3show signs of a transitory formation of 3T1,03.T120 on heating, but they behave diffeiently ahove 600' C. The chemically prepared substance alone shons two ranges of thermal stability TJsing 8-quinolinol as reagent, Bore11 and Paris (9) have shonn with the aid of the Chevenard thermobalance that the compound T1(CsH6SO)1.H20dehydrates very slowly a t temperatures ahove 44' C., but the change to the anhydrous salt is complete only a t 150" C. The range of stability of the latter is very narrow and it begins to decompoqe rapidly a t 165" C. Shove 380" C. it decomposes to finely divided metal and reoxidation is stated not to occur on further heating. These authors ( 1 0 ) also carried out the thermogravimeti ic analysis of trivalent thallium with 2-methyl-8-quinolinol and found that a t 80" to 145' C the compound obtained corresponded to the anhydrous methyl oxinate, TI(CBH&HBNO)I. Above this temperature decomposition occurred, leaving a residue of metallic thallium which n a s appreciably volatile a t TOO" C. AFTER OXIDATION WITH BROVINE. Earlier methods n hich recommended the use of bromine for the volumetric estimation of thallium, the color of the excess bromine indicating when the reaction mas complete, nere investigated by Browning (If). This procpdure was beset with many difficulties. Browning found that if the oxidized solution was treated with a slight excess of alkali hydroxide the immediate and complete precipitation of thallic hydroxide v-as effected Elements, the hydroxides of which are insoluble in excess sodium hydroxide or ammonium hydroxide, must be absent This necessitates the previous removal of thallium from most other elements. -4s THE IODATE. Recent17 Rao (42) reported the determination of thallium as the iodate. The results were fairly good but indicated that the solubility of the precipitate is appreciable.
110
ANALYTICAL CHEMISTRY
131 MEWS O F TETRLPHESYL 4RSOSIVRf CHLORIDE.Tetradetermination of thallium in solutions was reported by Solophenylarsonium chloride has been recommended by Smith (49) dovkin and Gusyatskaya (50). The determination of minute amounts of thallium in zinc sulfide ores has been described by as a reagent for the gravimetric estimation of thallium. When Strock (64) and Kui’mina (30). The determination of thallium thallium(II1) is present in solution with considerable hydroby the total energy method has been carried out by Marks and Any chloric acid it can be precipitated as (C~H5)4rlsT1C14. thallium(1) must first be oxidized. Potter (35), the results obtained agreeing well with chemical Volumetric Determination. WITH POTASSIUM PERMANGAanalyses. SATE. The titration of thallous salts with permanganate has An emission spectral analysis for the determination of thallium in parts of cadavers is stated by Jansch and LIayer ( 2 6 ) to give been described by Swift and Garner (55). Various modifications quantitative results when chemical methods prove inadequate. of the titration of thallous salts with potassium permanganate The spectrographic determination of thallium in animal tissues in hot hydrochloric acid solutions were tried by these workers, has also been described by Neveu (59). but the results were unsatisfactory. The use of the iodine Polarographic Determination. .Ensdin, Dreyer, and Abramonochloride end point gave erroneous results because of the catalyzed Oxidation of the iodine monochloride by the permanham (18) showed that small quantities of cadmium in metallic thallium, thallium in metallic cadmium, and thallium and cadganate. Beale, Hutchison, and Chandlee (4) report that thalmium in zinc or its alloys and its salts, can be determined polarolous salts can be titrated in hot 0.8 X hydrochloric acid under graphically in a strongly ammoniacal solution. The determinanitrogen with potassium permanganate to an electrometric end point or in hydrofluoric acid solution a t room temperature to a tion of small quantities of thallium and other metals in very visual end point. pure zinc was described by Cozzi ( I d ) , as little as 0.0001% of thallium being capable of determination polarographically. KITH CERICSULFATE. The use of ceric sulfate for the quantiSPECTROSCOPIC DETERMIXATIOS.The maximum sensitive tative oxidation of thallous salts was found to be unsatisfactory wave length and critical sensitivity of univalent thallium have by Swift and Garner (55). been determined spectroscopically by Toishi (56). WITH POTASSIUM IODATE. Sw-ift and Garner (65) found that thallous salts can be titrated precisely with 0.1 S potassium Determination of Micro Amounts of Thallium by Means of iodate in solutions which are 1 to 5 S in hydrochloric acid, with Artificial Radioactivity. This method has been described bv Moureu, Chovin, and Daudel (58). Thallium is precipitated as the iodine chloride end point. The end point was stated to be easier to find when the hydrochloric acid concentration was not thallous iodide, ivhich is made radioactive by using radioactive potassium iodide, or by bombarding the precipitated thallous less than 3 N . iodide directly with neutrons from a cyclotron. Amounts down WITH DITHIZONE.A titrimetric method has been described to 5 micrograms can be determined with an accuracy of 4 to 10%. by Kamerman (28),for the toxicological examination of viscera Chromatographic Determination. The use of chromatography for thallium, the recovery by this method being 96 to 100% as an auxiliary method in the microdetermination of thallium complete. was first reported by Schwab and Ghosh (46). The quantitative IODOMETRIC DETERMINATIOS.A method of this nature for the determination of 5 to 20 mg. of thallium in high percentage chromatographic determination of thallium was described by zinc and cadmium solutions has been reported by Kilian (29). -4nderson and Lederer ( 2 ) , who employed thick strips of filter paper pulp. Using a butanol-hydrochloric acid mixture as solIoDoirmRrc S E ~ ~ I ~ ~ I C R O D E T E ~ ~ Sill I I N Aand T I OPeterson B. vent, they separated trivalent thallium from iron, copper, nickel, (48) describe an iodometric method for the determination of and cobalt, and, after reduction of the thallium with sulfur thallium in ores and flue dusts, which is essentially stoichiometric. dioxide, precipitated It Tvith potassium chromate and weighed as Methods for the determination of thallium in toxicological thallous chromate. Starting Tvith 32.4 mg. of thallium, the materials were studied by Emara and Soliman ( l 7 ) , and that of precipitate obtained was equal to 32.8, 32.5, 31.9, 32.0, and 32.1 Fridle (23)was found to be the easiest and most reliable. mg. of thallium in different mixtures. BY ?rlEANSO F BROMOPHENOL BLUE.is z4DSORPTIONIKDICATOR. Potentiometric Determination. I n a recent review of the -4 new method for the volumetric estimation of thallium, using methods employed for the determination of thallium, Chretien bromophenol blue as adsorption indicator, is reported by Mehrota and Longi (IS) state that the best potentiometric method is that of (34). The titration is possible in the pH range of 4 to 8 and is Zintl and Rienacker (61),who used potassium bromate as reagent. not affected by the presence of calcium, barium, magnesium, Wj1lai-d and Young (60), using ceric sulfate, obtained results manganese, and sulfate ions. Lead ions interfere, but their which agreed closely 11ith those reported by Zintl and Rienacker interference can be prevented by previous precipitation as lead (61). The method proposed by Hollens and Spencer (25) sulfate. Thiocyanate and chromate ions also interfere. consists of converting the thallium to the trivalent state, adding SPECIAL METHODS FOR ESTIhlATION OF THALL1U.M potassium iodide to the acid solution, and titrating the liberated iodine with either arsenite or thiosulfate solution. The end Colorimetric Determination. Stitch ( 5 2 ) described a method point can be determined satisfactorily by means of the electrode for the colorimetric determination of thallium in 1929. The by Foulk and Ba-rden (22). Both reducing agents give repromethod described by Shaw (47) employs a Hellige wedge-type ducible end points down to 0.002 N solutions. The presence of colorimeter for the quantitative determination of thallium in iron and zinc does no harm, but copper behaves like thallium. tosicological materials, poison baits, or thallium salts. Bambach The titrimetric determination of thallium with potassium bromate (3) has determined small quantities of thallium in pharmaceutical in the presence of iron and its potentiometric titration in toxichemicals by a colorimetric method, using the mixed color cological materials has been recently described by Rienacker and technique. I n this method, the metal is extracted a t the proper Iinauel (43). They showed that the method of Zintl and RiepH with an excess of the reagent in chloroform. The excess nacker (61), in which thallium(1) is oxidized to thallium(II1) reagent is not removed, but is allowed to partition between the by a measured volume of potassium bromate solution, is accurate water and the organic solvent. The color of the extracted dithiin the presence of quinquevalent arsenic and antimony, quadrizonate is thus modified according to the relative quantities of valent tin, and most other cations, but gives poor results in the the metal and reagent present. The hue of the unknown solupresence of ferric iron, Del Fresno and Aguado (15) state that tion is matched against the hues of a standard series containing thallous salts may be potentiometrically titrated n ith chloramine known quantities of the metal. The analytical applications of in the presence of hydrochloric acid and potassium bromide 8-quinolinol derivatives of gallium and thallium have also been The results obtained by this method are said to be within 2% described by Moeller and Cohen (56). of the theoretical value. Spectrographic Determination. 4 spectral method for the
111
V O L U M E 25, N O . 1, J A N U A R Y 1 9 5 3 The method recornniended by Bertorelle and Tunesi (6)for the estimation of thallium in lead-thallium alloys is to titrate a hydrochloric acid solution of thallium in the univalent state with potassium permmganatc solution a t 30" to 40" in an apparatus equipped Lyith a perforated platinum electrode, glass stirrer, and a normal c:ilomel cell. The technique employed by Miura ( 3 5 ) is based o n the oxidation of thallium(1) which is contained in alkaline solution t,o thallic hydroxide by means of potassium ferricyanide solution. The titration must be carried out above 60' C. with vigorous stirring and in the presence of a large excess of alkali. Conductometric Determination. llaiiy incthods of this nature have been described. Ripan and Popper (44)state that thallous bromide is sufficicntly insoluhle so that 0.03 to 0.1 Jf thallous acetate can be titrated n-ith 1 -11potassium bromide conductometrically xvith satisfactory rcsults. Thallous chloride is the most solul)le of the thallous halides but 0.1 111 thallous acetate can be titrated with 1 JT potassium chloride if 25 to 50% of ethyl alcohol is present. These workcrs found that the thallous ferrocyanides have varying compositions, b u t that within a certain range, pure T14Fc(CS)Gcan br formed. I n the presence of calcium, a n insoluble compound containing both thallium and calcium is formed and 0.01 JI thallous acetate can be conductometricnlly titrated in the presence of an equivalent quantity of calcium with 0.1 Sf potassium ferrocyanide. I n three tests, the results agrrcd within 1% with those obtained by titration n-ith potassium chromate. Ripan and Popper also used potassium selenocyanate for the conductometric estimation of thallium. Using 0.025 Jf thallous acetate and 0.5 111 potassium selenocyanate, they found that thallium could be accurately determined in neutral or in hveakly alkalinr solutions. Electrolytic Determination. Chretien and Longi (IS) carried out, determinations of this type using a solution of thallous sulfate containing benzoic acid and dilute nitric acid, in conjunction with a mercury cathode. The results of five experiments with 0.016 to 0.162 gram of thallium were all high, with a maximum error of 6.23%. In thr presence of lead, good results were obtained with gallic acid replacing the benzoic acid. High results were also givrn xhen ethyl alcohol was present, owing to the oxidation of the thallium-mercury amalgam. I n concentrated nitric acid, the results obtained were much too IOTV, as was also true of elcctrolysis in the presence of ammonium hydroxide. According to Besson (8). the electrolytic deposition uscd for its precise determination. of thallium cannot Furthermore, he claims that the thallium deposited by the electrolysis of a nitric acid solution of its salt.- is in the form of the normal sesquioside, TlrOa, and not the dioxide, T102, or the intermediate oside. TI30j. However, the deposit cannot be used for determining thallium because it is difficult to obtain quantitatively. I n later investigations Besson (Y), compared numerous methods for the electrolyt,ic determination of thallium and stated that the cathodic deposition was quantitative but that the metal thus obtained was not adherent. I t was also very oxidizable and csould not be weighed. Satisfactory results were given only when a cathode made of \\-ood's alloy or of an amalgamated platinum cloth was used. Anodic deposition gave an adherent oside which could easily be weighed, but it was not quantitative, as part of the metal was deposited at thecathode. Recently, however, Sorwitz (40) has described a method for the electrolytic determination of thallium, which is stated to be accurate. The thallium is estimated by deposition on the anode as the oxide from an ammoniacal ammonium nitrate solution containing copper ions which act as a depolarizer and prevent t'he deposition of metallic thallium on the cathode. Some copper is deposited with the thallic oside; hence a correction must be made for that element. COULOMETRIC DETERHINATIOS.A coulometric titrat,ion is described by Buck, Farrington, and Swift (12) in which unipositive thallium is oridized to the tripositive state by elec-
c.
1 x 8
trolytically generated bromine or chlorine. The end point is determined amperometrically by measuring the current between two platinum electrodes having an impressed potential difference of 200 mv. Confirmatory titrations show average errorB of leoq than 0.2% for samples ranging from 93 to 1900 micrograms. SUMMARY
During the past 50 years much research has been diiected to the detection and quantitative determination of thallium. The detection of thallium is best carried out spectrographically, but fluorescence and micromethods are also extensively applied. There appears to be some contradiction regarding the fluorescence detection of thallium, one worker (24) stating that univalent thallium is like silver in quenching the fluorescence of uranil salts, while other aorkers (16) claim that thallium(1) form. a double salt with uranyl compounds which emit fluorescencc in the shoi t L\ avc-length visible hand. Of the numerous gravimetric method. described, perhaps that most worthy of retention is the detprmination of thallium 111precipitation as thallous chromate ( 3 7 ) , although precipitation as thallous iodide (31) is extensively applied. Many volumetric methods have been advocated. Thoie based on the titration of thallous salts with potassium pernianganate in hydrochloric acid solution are unsatisfactory, the w e of the iodine monochloride end point (55) giving erroneous results because of the catalyzed oxidization of the iodine monochloride by the permanganate. The application of ceric sulfate solution to the quantitative oxidation of thallous salts also gives unsatisfactory results, a n overconsumption of 0.6 to 2% of the oxidant occurring under certain conditions. Thallous salts, ho\Fever, can be precisely estimated by titration n i t h potassium iodate by means of the iodine monochloride end point. The end point is more rapidly attained when the hydrochloiic acid concentration is 3 S or greater. Of the various potentiometric methods described, that n hich uses potassium bromate as reagent i. perhaps the best, but is satisfactory only in the absence of ferric iron (43). The potentiometric titration of thallium(1) 4 ith chloramine T in the presence of hydrochloric acid and potassium bromide ( 1 5 ) yields results which are only within 2% of the theoretical value. The conductometric determination of thallium has also been investigated (44)and the titration of 0.01 iM thallous acetate with 0.1 31 potassium ferrocyanide, in the presence of a n equivalent quantity of calcium, yielded iesults which agreed within 1% of those obtained by titration nith potassium chromate. The conductometric titration of 0.025 Jf thallous acetate with 0.5 X potassium selenocyanate in neutral or weakly alkaline solutions, ho-ivever. gave quantitative results. Quantitative methods for thallium based on the solul)~lity of thallic chloride or bromide in ether have also been reported (58). The determination of thallium by electrodeposition hap received much attention in the last decade; the results obtained by both cathodic (8) and anodic ( 7 ) deposition are often far from precise. Recently, however, anodic deposition of thallium (40) from ammoniacal ammonium nitrate solution containing copper ions hah been reported as giving accurate results. The recent application of chiomatographic techniques to quantitative inorganic analysis may piove of value in the evolution of new methods for the separation and estimation of thallium. One such method ( 2 ) has been described in R-hich thallium(II1) was separatcd from iron, copper, nickel, and cobalt using butanol saturated Tiith 1 .Y hydrochloric acid, 99 to 100% recovery of thallium being obtained. LITERATURE CITED
112
ANALYTICAL CHEMISTRY
(3) Bambach, K., IND.ENG.CHEM.,ANAL.ED., 12, 63-6 (1940). (4) Beale, R. S., Hutchison, A. W,, and Chandlee, G. C., Ibid., 13, 240-2 (1941). (5) Berg, R., and Fahrenkamp, E. S., 2. anal. Chem., 109, 305-15 (1937). ( 6 ) Bertorelle, E., and Tunesi, A., Ann. Chim. (Rome),41, 34-42 (1951). (7) Besson, J., A n a l . Chim. A c t a , 3, 158-62 (1949). (8) Besson, J., Compt. rend., 224, 1226-7 (1947). (9) Borell, hl., and Paris, R., A n a l . C h i m . A c t a , 4 , 267-85 (1950). (10) Ibid., 5, 573-83 (1951). (11) Browning, P. E., IND.ESG. CHEM., ANAL.ED.,4 , 417 (1932). (12) Buck, R. P., Farrington, P.S., and Swift, E. H., ANAL.CHEM., 24, 1195-7 (1952). (13) Chretien, A., and Longi, I-., Bull. soc. chim., 11, 241-9 (1944). . Acta, 31, 37-41 (1943). (14) Corri, D., Mikrochemie xi’Mikrochim. (15) Del Fresno, C., and A1guado,rl., Z . anal. Chem., 109, 334-8 (1937). (16) de hfent, J.. and Dake, H. C., “Rarer llctals,” Xew Tork, Chemical Publishing Co., 1946. (17) Emara, M.,and Soliman. 121. A,, J . Roy. Egyptian M e d . .4sscrc., 32,895-905 (1949). (18) Ensslin, F., Dreyer, H., and .Ibraham, K., Metall und Erz, 39, 184-7 (1942). (19) Feigl, F., Nature, 161, 436 (1948). (20) Feigl, F., “Qualitative Analysis by Spot Tests,” 3rd ed., X e w York, Elsevier Publishing Co., 1946. (21) Forchheimer, 0. L., and Epple, R. P., ANAL.CHEM.,23, 1445-7 (1951). and Bawden T., .I. A m . Chena. Soc., 48, 2045(22) Foulk, C. W., 51 (1926). (23) Fridle, R., Deut. 2.ges. gerichtl. Med., 21, 461-2 (1933). (24) GotB, H., Science Repts., Tdhoku Imp. Univ., First Ser., 29, 204-18 (1940). (25) Hollens, A. R. A., and Spencer, J. F., A n a l y s t , 60, 672-6 (1935). (26) Jansch, H., and hiayer, F. X., Mikrochemie uer. Mikrochim. A c t a , 35, 310-19 (1950). (27) Jurang, H., Zbid., 34, 398-403 (1949). (28) Kamerman, P. A. E., J . S. A f r i c a n Chem. Inst., 27, 2 2 4 (1944). (29) Kilian, W., 2. Erzbergbari u. Metallhuttenw., 3, 281-4 (1950). (30) Kuz’mina, V. P., Zauodskaya Lab., 7, 579-81 (1938). (31) Lepper, W., 2. anal. Chem., 79, 321-4 (1930). (32) hfahr, C., and Ohle, B.. I b i d . , 115, 254-9 (1939). (33) Marks, G. W.,and Potter, E. V., L-. S. Bur. Mines, Rept. Inrest. 4461 (1949).
(34) (35) (36) (37) (38)
Mehrota, R. C., A n a l . Chim.A c t a , 3, 73-82 (1949). Miura, K., J . Electrochem. Soc. J a p a n , 19, 341-3 (1951). Moeller, T., and Cohen, A. J., ANAL.CHEM.,22, 68&90 (1950). Moser, L., and Brukl, A., Monatsh., 47, 709-25 (1927). hloureu, H., Chovin, P., and Daudel, P., Compt. rend., 219,
(39) (40) (41) (42) (43)
Neveu, N., Ann. pharm. franc., 8 , 214-16 (1950). Korwitr, G., A n a l . Chim. Acta, 5 , 518-20 (1951). Peltier, P., and Duval, C., Ibid., 2, 210-17 (1948). Rao, S. V. R., Current Sei. ( I n d i a ) , 16, 376 (1947). Rienacker, G., and Knauel. G., Z . anal. Chem., 128, 459-67
127-9 (1944),
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Accepted September 16, 1952.
Differential Multicomponent Spectrophotometry Spectrophotometric Method f o r Determination of Benzyl Benzoate and Acetanilide in Clothing Impregnant M-1960
N-Butyl
MORTON BEROZA Bureau of Entomology a n d Plant Quarantine, U . S . Department of Agriculture, Beltsville, M d .
D
IFFERENTIAL analyses have been shown to be very useful in markedly increasing the precision and accuracy of spectrophotometric analyses over those obtained by the conventional or absolute method for single components (1-8, IO). I n the absolute method the results are calculated in the usual manner from directly measured absorbancies and absorbancy indexes (9). I n differential analysis a solution of approximately known concentration is compared in a spectrophotometer with a solution of known and nearly identical concentration. (Differential analysis is referred to by some writers as analysis by relative transmittance or relative colorimetry.) By this means the differences in absorbancy are obtained and these data are used to calculate the unknown concentrations of substances. Recently Hiskey and Firestone (5) presented a differential method for the analysis of multicomponent mixtures that is in principle nearly identical with that of Jones, Clark, and Harrow (8), but is formulated for the analyst who may not possess a recording spectrophotometer and must rely on a few discrete measurements. The present method ha8 been formulated with the same purpose in mind.
The method is simple, accurate, and generally applicable even to those systems that do not follow the absorption laws. I n the method of Hiskey and Firestone for a two-component system the absorbancy difference between an unknown solution of high absorbancy and a reference standard of one of the components is determined a t the wave length of that component’s absorption peak. The absorbancy difference between the unknown solution and the reference standard of the second component is then determined a t the wave length of the second component’s absorption peak. With this method deviations from Beer’s law cannot be tolerated and the absorbancies of the constituents must be additive. The method is therefore limited to well-established systems t h a t show no deviations from absorption laws even with solutions of high absorbancy. The present method is considerably less affected by these limitations. Essentially it involves the determination of the absorbancy differences between a solution containing known ingredients and one containing almost the same concentrations of those ingredients, The latter solution is prepared so as to con-
