essentially complete in ethanol and methanol but the results in aqueous ethanol would not be consistent. There would appear to be two possible reactions which could occur between sulfite ion and mercuric thiocyanate, although none seems to have been reported in the literature. Sulfite does form very stable complexes with mercury(I1) species, one of which is used to stabilize the ion for colorimetric estimation using the West-Gaeke procedure (14). Sulfite is also known to reduce mercury(I1) to mercury(1) under some conditions (15). It was not possible to determine, on the basis of this work, the nature of the reaction occurring. The investigation did show that no reaction took place in water alone, ethanol or methanol being required. The reaction required 15-30 minutes for completion in aqueous ethanol, and the extent of reaction was possibly in the range of 5@-90% depending on the stoichiometry assumed. This procedure is relatively simple, requires only a short amount of time and a minimum amount of manipulation. No separation step, filtration, or centrifugation, is needed as is the case with a similar reaction employing mercuric chlor(14) P. W. West and G. C. Gaeke, ANAL.CHEM., 28,1816 (1956). (15) L. M. Stewart and W. Wardlaw, J. Chem. SOC.,121, 1481 (1922).
anilate (16). The disadvantages would seem to be the somewhat low molar absorptivity of the ferric thiocyanate complex and the tendency for the color to fade. The visible absorption of the FeSCN2+ species is considerably higher than that of the chloranilate ion. The precision in both the chloranilate and thiocyanate methods is possibly somewhat lower than with other colorimetric procedures. Serious interferences would be expected if bromide, bromate, chloride, cyanide, iodate, iodide, nitrite, sulfide, or thiosulfate ions were present since each of these anions has been determined by this procedure. Since chloride is routinely measured by this method, these possible interferences apparently are not serious in that analysis. Our results indicate that sulfite does not react with mercuric thiocyanate in water only but requires the presence of ethanol or methanol. It might be possible to detect interferences by utilizing this difference, assuming that all of the other anions do react in water alone. RECEIVED for review January 27, 1972. Accepted March 17, 1972. The authors express their appreciation to the Robert A. Welch Foundation of Houston, Texas, for support of this research. ~
(16) R. E. Humphrey and W. Hinze, ANAL.CHEM.,43, 1100 (1971).
Trimethylphenylammonium Bromide as a Selective Quantitative Precipitant for Gold or Thallium W. W. White Industrial Laboratory, Kodak Park Diuision, Eastman Kodak Company, Rochester, N . Y . 14650
A RAPID SEMIMICRO METHOD is described for the gravimetric determination of gold or thallium in quantities of 10 to 60 mg by use of trimethylphenylammonium bromide (TMPB). The method represents a unique use of the reagent. The scarcity of information concerning the use of quaternary organic ammonium compounds that precipitate and provide direct weighing forms for anionic metal complexes suggests a fertile and useful area of analytical investigation. In this paper, TMPB was studied and found to be a selective quantitative precipitant for gold or thallium. The stable tetrabromo complexes of gold(II1) and thallium(II1) are precipitated with TMPB to form A B X l structures, where A is the quaternary cation [(CH3)3(C6HJNJ, B is the metal, and X is the bromide. In previous articles, White and Zuber have described gravimetric methods using trimethylphenylammonium iodide (TMPI) to determine mercury, lead, platinum ( I ) , and gold (2). Cadmium (3) and bismuth ( 4 ) have also been determined using TMPI. The speed of analysis, selectivity, flocculent nature of the precipitates, and favorable gravimetric conversion factors are the attractive features of these two reagents. (1) W. W. Whiteand J. R. Zuber, ANAL.CHEM., 39,258 (1967). (2) Zbid.,36,2363 (1964). (3) A. Pass and A. M . Ward, Aiialyst (Londo/r),58,667 (1933). (4) T. S. Burkhalter and J. F. Solarek, ANAL.CHEM.,25,1125 ( 195 3).
Beamish, in his review of gravimetric methods for the determination of noble metals, states that relatively few organic precipitants give direct weighing forms for gold ( 5 ) . The classical reduction methods (6) are time-consuming and in most cases require the removal of nitrate prior to the reduction to the metal. Most of the chemical methods for the determination of thallium require its reduction to the monovalent state. The precipitation of thallium(1) with potassium chromate has been the most frequently used gravimetric method. Many elements interfere unless steps are taken to mask or separate them from thallium. Kodama (7) gives a summary of the important chemical methods used to determine the element including the use of colorimetric methods. The proposed method for gold or thallium is simple, accurate, and requires no reduction of these elements to the monovalent or elemental state after the dissolution of the sample. Thirty-one elements were shown not to interfere with the gold or thallium determinations.
(5) F. E. Beamish, Tulai~ta,13,773 (1966). (6) W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, and J. I. Hoffman, “Applied Inorganic Analysis,” 2nd ed., Wiley, New York, N.Y., 1953,pp 366-7. (7) K. Kodama, “Methods of Quantitative Inorganic Analysis,” Interscience, New York, N.Y., 1963. ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
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Table I. Results of Gold and Thallium Determinations Weight of Au or T1 Au found, T1 found, taken, mg mg Error, mg Error, 10.0 10.1 1.o 10.2 2.0 0.0 20.1 0.5 20.0 20.0 30.0 30.2 0.7 30.3 1 .o 40.0 40.0 0.0 39.5 1.3 50.0 50.0 0.0 50.0 0.0 60.0 59.9 0.2 59.5 0.8
z
z
Table 11. Recovery of Gold or Thallium from Synthetic Samples 50 mg of each element5 added to 50.0 mg of Au Au found, T1 found, Error, % mg Error, or T1 mg 0.4 49.2 1.6 Ad 49.8 A1 49.5 1.o 49.5 1. o As 49.8 0.4 49.5 1 .o Ba 50.1 0.2 49.8 0.4 Be 50.0 0.0 0.4 49.8 Ca 50.0 0.0 49.6 0.8 co 50.1 50.3 0.6 0.2 Cr 49.9 49.5 1 .o 0.2 cu 50.4 0.8 49.6 0.8 Fe 50.3 0.6 49.6 0.8 Ga 50.0 0.0 50.1 0.2 In 49.9 0.2 49.5 1 .o K 50.0 0.0 50.0 0.0 La 49.8 0.4 50.0 0.0 Li 49.6 0.8 49.7 0.6 49.7 0.6 1 .o Mg 49.5 0.6 Mn 49.7 50.0 0.0 Mo 50.3 49.9 0.2 0.6 1.2 Ni 49.4 49.8 0.4 1 .o Pbb 49.5 50.9 1.8 Re 49.8 49.6 0.8 0.4 Ru 49.5 50.0 1 .o 0.c Se 49.6 0.8 49.5 1 .o Sn 50.1 0.2 50.6 1.2 Sr 50.2 0.4 49.8 0.4 Te 50.4 50.3 0.6 0.8 51 .O 0.4 Ti 49.8 2.0 0.4 50.1 0.2 U 49.8 0.8 51 .O V 49.6 2.0 Zn 49.9 0.2 49.8 0.4 Zr 50.3 50.0 0.6 0.0 Re1 error 0 . 5% Re1 error 0 , 7 Range 1 . 0 mg Range 1 .8 mg Standard 0.3 mg Standard 0.4 mg dev dev a All elements were added as chloride salts with the following exceptions: AgN03, NaAsOn,La203,HzM004, Pb(N03)~,Se, Te, UsOe,V 2 0 sand , Zr (SO&. b Elements that were separated as the bromide before the addition of TMPB. EXPERIMENTAL
Reagents. Trimethylphenylammonium bromide-sodium bromide solution is prepared by dissolving 28 grams of the reagent (Eastman Organic Chemicals No. 9095) and 16 grams of sodium bromide in 1 liter of distilled water. The solution is stable for at least two weeks. The wash solution is prepared by adding 15 ml of concentrated hydrobromic acid to 370 ml of the trimethylphenylammonium bromide-sodium bromide solution and diluting to 500 ml with distilled water. The gold used in the experiments was 99.999% pure and the thallium used was purified thallium(1) nitrate assayed at 100.0%. 1514
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
Procedure. A weighed sample containing 10 to 60 mg of gold or thallium is transferred to a 250-ml beaker. The sample is dissolved in 10 ml of aqua regia and the solution evaporated to approximately 2 ml on the steam bath. The sides of the beaker are washed down with approximately 5 ml of water. Forty milliliters of water, 3 ml of concentrated hydrobromic acid, and 65 ml of the TMPB-NaBr solution are added to the beaker. The beaker is placed in a water bath at approximately 15 "C. The precipitate is stirred intermittently for 60 minutes. With stirring, the precipitate becomes flocculent. The precipitate is suction-filtered onto a tared Gooch crucible. The beaker and precipitate are washed sparingly with the wash solution and then with 15 ml of toluene. The precipitate is allowed to partially dry while still on the suction flask by passing air through the crucible for approximately 5 minutes. The crucible is dried in a drying oven for approximately 15 minutes at 80 "C. The conversion factors for gold and thallium are 0.3017 and 0.3095, respectively. RESULTS AND DISCUSSION
Under the analytical conditions described in the Experimental section, bismuth, cadmium, iridium, mercury, osmium, palladium, platinum, and rhodium precipitate as a group or in some cases individually when their acid solutions are treated with TMPB-NaBr. However, the problems involved in obtaining stable insoluble precipitates with these elements were not solved. Solutions containing chloroplatinic acid that were boiled with sodium bromide and then treated with TMPB produced orange precipitates which conformed to the AzBXe structure. The platinum-TMPB precipitates gave close to 100% recovery of platinum in samples analyzed. However, the addition of foreign ions led to incomplete precipitation. Therefore, it was concluded that TMPB has little to offer as an analytical precipitant for platinum. Toluene is used as a secondary wash solution in the gold or thallium method to remove the small amount of excess reagent remaining in the precipitates. Toluene wash solutions containing varying amounts of ethanol were unacceptable since they had a solvent effect on the gold, thallium-TMPB precipitates. Table I shows the analytical results obtained when known quantities of gold(II1) or thallium(II1) were evaluated. The values show that gold or thallium can be determined accurately within a 10- to 60-mg range. The average error was less than 1 % for the determination of both elements. Low results were experienced when less than 5 mg of each element were taken and slightly high results, due to occluded reagent, were observed when quantities exceeded 75 mg. Table I1 shows the results obtained when synthetic samples containing 50.0 mg of gold or thallium were analyzed. At the 50.0-mg level, relative errors of 0.5 and 0.7% were observed for the gold and thallium determinations, respectively. No observable interferences were detected from the synthetic samples which represented a study of 31 elements. Gold. Residual nitrate from the decomposition of the samples does not interfere with the analysis. Some oxidation of the bromide by the nitrate ion can cause a yellowish color to appear in solution. The rust-brown [(CH3)3(C6H5)N]+AuBr4compound is easy to filter and seldom adheres to the sides of the beaker. A constant weight is obtained by drying the gold-TMPB precipitate at 80 "C. The precipitate is nonhygroscopic. Component analysis of the precipitate gave the following results: 30.1 % Au, 20.9% [(CH3)&H5)N], and 49.0% Br. The
Thallium forms a white compound with TMPB and has the formula [(CH3)3(C6Hj)N]+TIBr4-. The precipitate is easily filtered and, when dry, is nonhygroscopic. A light blue color is sometimes observed after drying the precipitate. This is due to a trace of oxidized reagent and does not affect the results of the thallium determination. Component analysis of the thallium-TMPB precipitate gave the following results: 30.9% TI, 20.7% [(CH3),(CbH5)N], and 4 8 . 4 z Br. The stoichiometry of the compound requires 30.95 % TI, 20.63 % [(CH3)&H5)N], and 48.42 % Br. Applications for the proposed thallium method may be found in the analysis of rodenticides, insecticides, alloys, various inorganic salts, thallium catalysts, and thallium depilatory agents.
stoichiometry of the A B X 4 compound requires 30.17% Au, 20.87% [(CH3)3(C6H~)N], and 48.96% Br. No sodium citrate is needed in the proposed method to keep the copper(II), iron(III), and tin(1V) complexed to prevent interference as is the case in the gold-TMPI method (2). Also the chance of reducing gold from solution is eliminated by not using the sodium citrate. Applications for the proposed gold method may be found in gold-plated materials, diverse inorganic salts, and in alloys containing gold, silver, and lead where the silver and lead can be first separated as the bromide. Bismuth, cadmium, iridium, mercury, osmium, palladium, platinum, and rhodium interfere with the gold and thallium determinations. Small quantities of these elements coprecipitated with the gold, thallium-TMPB. ‘Thallium. Samples treated with aqua regia will oxidize thallium to the trivalent state. Dilute solutions of aqua regia were ineffective for the complete oxidation of thallium.
RECEIVED for review January 14, 1972. Accepted March 17, 1972.
Spectrophotometric Determination of Sulfur Dioxide by Reduction of Iron(ll1) in the Presence of Ferrozine Amir Attari’ and Bruno Jaselskis Department of Chemistry, Loyola Uniaersity, Chicago, Ill. 60626
DETERMINATION OF MICRO AMOUNTS of sulfur dioxide in air and in liquid samples has been described by using iron(II1) in the presence of 1,IO-phenanthroline ( 1 , 2 ) and 2,4,6-tri(2pyridyl)-l,3,5-triazine (3). Sulfur dioxide in both methods reduces iron(II1) and in the presence of 1,lo-phenanthroline and 2,4,6-tri(2-pyridyl)-1,3,5-triazine yields corresponding iron(I1) chelates having molar absorptivities of 1.1 X 104M-lcm-I at 510 nm and 2.2 X lO4M-’crn-’ at 593 nm, respectively. However, the stoichiometry in both methods depends on temperature and the determination must be carried out under carefully controlled conditions. In a recent paper Stookey ( 4 ) describes a method for the determination of micro amounts of iron(I1) using 3-(2-pyridyl)-5,6-bis(4-phenyl sulfonic acid)-l,2,4-triazine disodium salt, ferrozine. The ferrozine reagent is soluble not only in aqueous solutions but also with iron(I1) forms highly colored chelate having molar absorptivity of 2.8 X lO4M-’crn-l at 562 nm. Because of these qualities, the reaction of sulfur dioxide with iron(II1) in the presence of ferrozine has been investigated and is reported in this note. EXPERIMENTAL
Apparatus. A Cary Model 14 and Beckman DB Spectrophotometers were used for the absorbance measurements. The pH of the solutions was determined by a Corning Model 1 Present address, Institute of Gas Technology, Chicago Ill. 60616.
(1) B. G. Stephens and F. Lindstrom, ANAL.CHEM.,36, 1308
(1964). (2) Amir Attari, T. P. Igelski, and B. Jaselskis, ibid.,42,1282 (1970). (3) B. G . Stephens and H. A. Suddeth, Aiialyst ( L o d o n ) , 95, 70 (1970). (4) L. Stookey, ANAL.CHEM., 42,779 (1970).
12 research pH meter. Known amounts of sulfur dioxide were introduced into the absorption flask either from a standard aqueous solution or from a gas flow system as described in our previous work (2). The absorption train for the standard sulfur dioxide atmosphere contained a supply of purified air or nitrogen, a flow meter, a constant temperature (22 “C) enclosure for the permeation tube followed by a copper sulfate on pumice absorption tube and a gas washing bottle for the absorption of sulfur dioxide thermostated at various temperatures. A Sage syringe was used to inject the interfering gases into the gas stream. Atmospheric sulfur dioxide was measured after drawing the air with a pump through a Brooks flow meter, the copper sulfate on pumice absorption tube (5)and then through the gas washing bottle. Reagents. A permeation tube (6, 7) containing liquid sulfur dioxide with diffusion rate of 1.008 pg of sulfur dioxide per minute was obtained from Analytical Development, Inc. The permeation rate of SO2 was determined accurately after the conversion of SOn to hydrogen sulfide using a high temperature catalytic hydrogenation method (8, 9). Aqueous sulfur dioxide (2 to 4 X 10-4M) solutions were prepared by dissolving reagent grade sodium bisulfite in deaerated 5 glycerol in water solution. The solution was stored in a Machlett buret under nitrogen and was daily analyzed for sulfur dioxide by the iodimetric method. A 0.0025M ferric solution was prepared by dissolving the Baker Analyzed ferric ammonium sulfate in 0.1M perchloric acid. The dissolution “Applied Inorganic Analysis,” 2nd ed., W. Hillebrand, G. E. F. Lundell, H. A. Bright, and J. L. Hoffman, Ed., John Wiley & Sons, New York, N. Y., 1955, pp 768-9. (6) A. E. O’Keefe and G. C. Ortman, ANAL.CHEM., 36,1308 (1964). (7) F. P. Scaringelli, S. A. Frey, and B. E. Saltzrnan, Amer. hi. H y g . Ass.J.,28,260(1967). (8) D. M. Mason. Hydrocrirbon Process., 43,145 (1964). (9) W. W. Scott, “Standard Methods of Chemical Analysis,” 5th ed., N. H. Furman, Ed., D. Van Nostrand Co., New York, N . Y . , vol. 11,1939. (5)
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