dioxide for the range of concentrations of 1 to 75 ppm are the phenol-disulfonic acid technique (ASTM D 1608-60) and the Saltzmann technique (13). The phenol-disulfonic acid method requires 1-liter samples and has given in this laboratory an average absolute deviation of 6% and a standard deviation of 3 ppm. The Saltzmann procedure requires 250-cc samples. An average absolute deviation of 3-4 % has been reported (13) in the concentration range from 8 t o 45 ppm. The phenoldisulfonic acid method is used for the determination of the total nitrogen oxides as nitrogen dioxide, whereas the Saltzmann procedure is used for the analysis of only nitrogen dioxide in the presence of any other nitrogen oxides. Because (13) B. E. Saltzmann, ANAL.CHEM.,26, 1949 (1954).
the analysis time is 5 min. for gas chromatography cs. 3 to 4 days with the phenol-disulfonic acid method and the sample size is 0.5 cc us. nominally 1 liter, the analysis by gas chromatography shows advantages for the conditions studied. Sample size would be the main advantage relative to the Saltzmann procedure.
for review May 11, 1966. Accepted September 26, 1966. The research project was financed by the Division of ~i~ pollution, Bureau of State Services, United States public Health Service. Fellowship support for M, E. Morrison was contributed by the Dow Chemic; Co. and the Union Carbide Corp.
RECEIVED
Gravimetric Determination of Mercury, Lead, and Platinum Using Trirnethylphenylammonium Iodide W. W. White and J. R. Zuber Electronic Componenfsand Decices, Radio Corp. of America, Someroille, N. J. 08876
RAPIDSEMIMICRO METHODS are described for the gravimetric determination of Hg(II), Pb(II), and Pt(1V) in quantities of 4 t o 60 mg in various complex matrices by use of trimethylphenyiammonium iodide (TMPI). This reagent was used first by Pass and Ward (1) t o determine cadmium in the presence of zinc. The reagent was utilized further by Burkhalter and Solarek ( 2 ) for the gravimetric determination of bismuth and by White and Zuber (3) for the gravimetric determination of gold. Other organic reagents have been reported to precipitate the halide complexes of mercury and platinum but each reagent has its own degree of selectivity (4). Ethylenediamine or propylenediamine, each in the presence of copper sulfate, precipitates the Hg14-2 complex (5) whereas cinchonine, quinine, or hexamine each precipitates with iodoplatinic acid (6). Tetraphenylarsonium bromide has been used to give a precipitate with the PtBr8-z complex (7). Relatively few organic compounds, however, have been reported for precipitating platinum, as indicated by Beamish in his recent review of gravimetric methods for the determination of the noble metals (8). Picrolonic acid (9), sodium anthranilate ( I O ) , and thionalide (11) are used to determine milligram quantities of lead, but (1) A. Pass and A. M. Ward, Analyst, 58,667 (1933). (2) T. S. Burkhalter and J. F. Solarek, ANAL.CHEM.,25, 1125-6 (1953). (3) W. W. White and J. R. Zuber, Ibid..36, 2363-4 (1964). (4) K. Kodama, “Methods of Quantitative Inorganic Analysis,” Interscience, New York, 1963. (5) Ibid.,p. 153.
(6) S . Takagi and Y. Nagase, J. Pharm. SOC.Japan, 58, 60-6 (1938). (7) H. Bode, 2. Anal. Chem., 133, 95 (1951). (8) F. E. Beamish, Talanta, 13, 773-801 (1966). (9) H. Imai, J. Chem. SOC.Japan, 76, 770 (1955). (10) J. F. Welcher, “Organic Analytical Reagents,” Vol. 11, p. 200, Van Nostrand, New York, 1947. (11) K. Kodama, “Methods of Quantitative Inorganic Analysis,” p. 160, Interscience, New York, 1963. 258
ANALYTICAL CHEMISTRY
many cations interfere. The precipitation of lead as the sulfate from dilute sulfuric acid solutions is not entirely quantitative (12). The addition of alcohol reduces the solubility but a t the same time increases contamination by elements such as bismuth, calcium, and silver. The electrodeposition of lead as the dioxide is a n accurate method; however, arsenic, chloride, cobalt, manganese, and many other elements interfere (13). EXPERIMENTAL
Reagents. The precipitating solution for mercury and lead is prepared by dissolving 60 grams of potassium iodide and 25 grams of trimethylphenylammonium iodide (Eastman Organic Chemicals, reagent 4423) in 1 liter of water. The mercury wash solution is prepared by diluting 1 part of the precipitating solution with 4 parts of water. The solution is stable for several weeks. The lead wash solution is prepared by acidifying the above wash solution with hydrochloric acid to give a 2x acid solution by volume. This solution remains stable for only a few hours. The toluene wash solution is prepared by adding 25 ml of ethanol to 1 liter of toluene. The buffer and complexing solution is prepared by dissolving 150 grams of sodium citrate dihydrate and 200 grams of anhydrous sodium acetate in warm water and diluting to 1 liter. The mercury and lead standard solutions are prepared by weighing 1.0000 gram of each metal, dissolving carefully in dilute nitric acid, and diluting separately to 0.5 liter with distilled water. The platinum standard solution is prepared by weighing 1.0000 gram of the metal, dissolving in aqua regia, and diluting to 0.5 liter with water. (12) W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, and J. I. Hoffman, “Applied Inorganic Analysis,” 2nd ed., p. 227, Wiley,
New York, 1953. (13) K. Kodama, “Methods of Quantitative Inorganic Analysis,” p. 158, Interscience, New York, 1963.
Procedure for Mercury. Weigh a sample containing 5 to 60 mg of mercury or, for evaluation purposes, transfer by pipet an aliquot of the standard mercury solution to a 250-ml beaker, Add 5 ml each of nitric and sulfuric acid and evaporate on the hot plate to the appearance of sulfur trioxide fumes, Fume the sample for about 3 min, then cool to room temperature. Add 35 in1 of distilled water and heat if necessary to dissolve the salts. Cool and add 15 ml of the buffer and complexing soluticn. Adjust the pH to 4.3-4.7 using ammonium hydrox;de and sulfuric acid, and again cool the solution to room temperature. Add an ice cube (-35 cm3, made from distilled water) to the solution and then add 30 ml of the precipitating solution. With stirring, the cream-colored precipitate becomes flocculent. Filter onto a tared Gooch crucible as soon as the ice cube melts. Wash the precipitate using 5 to 10 ml of the mercury wash solution. Then wash out the free reagent remaining in the precipitate using approximately 30 ml of the toluene wash solution. Dry the precipitate for 30 minute at 100" C. The conversion factor for mercury is 0.2045. Procedure for Lead. Weigh a sample containing 4 to 60 mg of lead or, for evaluation purposes, transfer by pipet an aliquot of the standard lead solution to a 250-ml beaker. Add 8 ml of aqua regia to the sample and evaporate slowly to a paste. Add 10 ml of hydrochloric acid and repeat the evaporation process. Then add 2 ml of hydrochloric acid and 40 ml of water and wmm to dissolve the salts. Add 5 ml of sulfurous acid (6z SOn)and stir. The addition of sulfurous acid must be omitted if barium or strontium are present because they form insoluble sulfites and/or sulfates. Add an ice cube (-35 cm3, made from distilled water) and then add 30 ml of the precipitating solution. Stir until the canary-yellow precipitate has coagulated. Filter, wash (using the lead and toluene wash solutions), and dry the precipitate as described in the procedure for mercury. The conversion factor for lead is 0.2861. Procedure for Platinum. Weigh a sample containing 4 to 60 mg of platinum or, for evaluation purposes, transfer by pipet an aliquot of the standard platinum solution to a 250-ml beaker. Add 10 ml of aqua regia to the sample and evaporate to dryness on the steam bath. Add hydrochloric acid and again evaporate to dryness. Repeat this step until the nitrates have been expelled. Add 1 mI of hydrochloric acid and 25 ml of water and warm to dissolve the salts. Add 1.8 grams of potassium iodide and gently boil the solution for one minute. Cool to room temperature and add 30 ml of a 3.5 trimethylphenylammon~um iodide solution containing no potassium iodide. Stir the brown-black precipitate and allow it to stand for 10 minules. Add an ice cube as in the mercury procedure. When the ice has melted, filter, wash, and dry the precipitate as stated in the procedure for mercury. The conversion factor for platinum is 0.1587.
RESULTS AND DISCUSSION Trimethylphenylammonium iodide tends to precipitate those elements which readily form stable anionic complexes with iodide. Table I shows the elements that are known to form iodo complexes that react with TMPI to give colored precipitates. Antimony, arsenic, copper, iridium, iron, osmium, palladium, rhodium, ruthenium, silver, tellurium, and tin were precipitated by this reagent, but difficulties were encountered in obtaining stable and/or quantitative precipitates. Halogen-bridged anionic complexes have been reported by Harris, Livingstone, and Stephenson (14). By treating bivalent palladium and platinum with TMPI they obtained A2B2X6structures, where A is the quaternary cation [(CH&(14) C. M. Harris, S. E. Livingstone, and N. C. Stephenson, J. Chem. Soc., 1958,36973702.
Table I. Elements Forming Precipitates with Trimethylphenylammonium Iodide
Elements shown in the solid blocks are those known to precipitate with TMPI. Elements circled represent those that have been determined using TMPI.
Table 11. Accuracy of Method for Mercury, Lead, and Platinum Diverse ions added, in quantities of 80 mg eacha Ga(III), In(III), Zn(I1) Co(II), Ga(III), Ni(II)* Cu(II), Fe(II1) Sn(IV) Al(III), V(V) Be(II), Zn(1I)b Li(I), Rb(I), Te(IV) As(V), Mn(I1)h Cr(III), Mg(II), Fe(I1I) Ca(II), Co(II), Cu(I1)
Weight of mercury, mg Taken Found 5.0 10.0 11 .o 12.0 14.0 20.0 30.0 40.0 50.0 60.0
5.0 10.1 11.1 11.9 14.2 20.0 29.9 40.0 50.0 59.8 Mean rel. error
Rel. error, 0.0 1 .o 0.9 0.8
1.4 0.2 0.3 0.5 0.0 0.3 0.5
Weight of lead, mg Al(III), Be(II), In(II1) Fe(III), Ni(II), Pt(1V) Co(II), Ga(III), Ni(1I)b Ga(III), Zn(I1) Ba(II), Ca(II), Mg(II), Sr(I1) Al(III), Cr(II1) As(V), Mn(I1) Li(I), Na(I), Rb(Ir Ba(II), Th(1V) Mg(II), V(V)
4.0 6.0 10.0 12.0 14.0 20.0 30.0 40.0 50.0 60.0
4.0 5.9 10.1 12.1 13.9 20.1 30.4 40.1 50.0 60.3
0.0 1.7 1.0 0.8
0.7 0.5 1.3 0.2 0.0 0.5 Mean rel. error 0 . 7
Weight of platinum, mg Al(III), Ga(II1) Be(II), In(II1) Co(II), Ni(II), Zn(II)b Cr(III), Th(1V) Mn(II), V(V)*
Ba(II), Ca(II), Mg(II), Sr(I1)
4.0 6.0 10.0 20.0 40.0 60.0
4.1 6.1 10.0 20.0 39.9 59.8
2.5 1.7 0.0 0.0 0.1 0.3 Mean rel. error 0 . 5
a In the mercury method the diverse ions were added as the nitrate or sulfate salts with the exception of gallium, indium, tellurium, and vanadium, which were added as elements; in the lead and platinum methods the diverse ions were added as chloride salts, with the same exceptions noted above. In the mercury and lead methods, arsenic was added as the oxide. Average of 3 determinations.
(CsHa)N], B is the metal, and X is the iodide. It is believed that lead also forms the AzB2X6 dimer. Au(II1) (3) and Bi(II1) ( 2 ) form A B X 4 compounds whereas Cd(I1) (I) and Hg(I1) form the A z B X l type. Pt(1V) was found to be A 2 B X e in composition. Chemical analyses of the lead, mercury, and platinum precipitates confirm theoretical stoichiometry. Mercury. Table I1 shows the results obtained with samples containing known quantities of mercury doped with diverse ions, in order to detect possible interference. An equal VOL. 39, NO. 2, FEBRUARY 1967
259
number of determinations in the same milligram range were made without diverse ions present. Results showed an average relative error of 0.5 Z. The given pH range must be maintained in order to keep stable the mercury TMPI complex and to keep effective the masking of As(V), Cu(II), Fe(III), Sn(IV), and Te(1V) with sodium citrate. Selenium, thallium, and the elements not masked by sodium citrate within the solid blocks in Table I interfere. EDTA cannot be used as a masking agent. In strongly acidic solutions it precipitates as the free acid, and in weakly acidic solutions it prevents the precipitation of mercury. Lead. Table 11 shows the results for lead samples containing diverse ions. An average relative error of 0.7z was obtained. The same quantities of lead without diverse ions present were determined, and an average relative error of 0.5z was found. Lead is precipitated best with TMPI from 2-6 vjv hydrochloric acid solutions. Sulfurous acid is added to solutions containing As(V), Fe(III), and Pt(1V) to reduce their valence state, thus preventing coprecipitation with the lead. Samples containing no barium or strontium can be fumed to dryness using a mixture of sulfuric and hydrobromic acids, thus avoiding interference from antimony, mercury, selenium, and tin. The lead sulfate resulting from the fuming is dissolved in 5 ml of hydrochloric acid followed by 40 ml of water. The general procedure is now resumed. A distinct advantage of the proposed method over the classical lead sulfate methods is that small quantities of lead can be determined in the presence of relatively large quantities of barium and strontium. This aspect becomes most attractive, for example, when analyzing for lead in a leadbarium-zinc silicate. A sodium carbonate fusion, leached in hydrochloric acid, followed by a silica dehydration separation can provide the conditions under which an accurate deter-
z
mination of lead is made possible in the presence of barium. The volume of the solution containing lead ions should be kept under 50 ml before the ice cube and the precipitant are added. Platinum. Table I1 shows the results for platinum samples containing diverse ions. An average relative error of 0.5 % was obtained. Twenty additional determinations were made with no diverse ions present. The results again showed a mean relative error of 0.5 %. It is necessary to heat the chloroplatinic acid solutions in the presence of excess iodide to get complete transition from a chloro to an iodo complex. Iridium and ruthenium were found to be even more sluggish in forming complexes with iodide. Applications for the proposed method may be found in platinum-plated materials and in alloys containing gold and silver where silver can be separated as the chloride and gold reduced to the metallic state. The reducing agent should be destroyed and the platinum oxidized back to the quadrivalent state. Copper and iron, along with many other cations, can be easily separated from platinum by passing a weakly acidic chloride solution through a suitable cation-exchanger in the hydrogen form (15, 16). The effluent can be evaporated and the platinum precipitated with TMPI as described in the procedure. Table I shows the elements that are known to coprecipitate with platinum if no separations are made. Selenium and thallium interfere. RECEIVED for review September 9,1966. 2, 1966.
Accepted November
(15) C. K. Butler, Znd. Eng. Chem., 48, 711 (1956). (16) H. G. Coburn, F. E. Beamish, and C. L. Lewis, ANAL.CHEM., 28, 1297 (1956).
Polarographic Determination of Sulfur Dioxide in Mercury(l1)-Sulfur Dioxide Complex Leonard L. Ciacciol and Thano CotsisZ Research Department, T . J . Lipton, Inc., Englewood Cliffs,N . J .
THE USE OF SODIUM TETRACHLOROMERCURATE(~~)for an SOz absorber for atmospheric samples as proposed by West and Gaeke (1) was extended to use in the detection of SOnin foodstuffs (2, 3, 4). SOn in the sodium tetrachlorate mercurate solutions was determined by the pararosaniline method ( I ) . However, a much larger range of SOn concentrations can be Present address, Central Research, Wallace & Tiernan, Inc., Newark, N. J. 2 Present address, Avon Products, Inc., Suffern, N. Y. (1) P. W. West and G. C. Gaeke, ANAL.CHEM., 28, 1816 (1956). (2) E. B. Beetch and L. J. Oetzel, J. Agr. Food Chern., 5,951 (1957). (3) J. E. Brekke, J. Assoc. Ofic.Agr. Chemists, 44,641 (1961). (4) F. S. Nurv. D. H. Taylor, J. Agr. Food Chem., . . and J. E. Brekke,.~ 7, 351 (1959). (5) I. M. Kolthoff and C. S. Miller, J . Am. Chem. Soc., 63, 2818 (1941). \
,
260
ANALYTICAL CHEMISTRY
accommodated by the polarographic analysis (10 to 1000 pg per ml) than by the colorimetric method (0.2 to 2 pg per ml), although the colorimetric method is much more sensitive. For a sampling situation where the SOz content is not known, a polarographic procedure capable of such wide ranges in concentration would be of great advantage. In this laboratory, the reported distillation procedure (2) was used in modified form for the determination of SOyin foodstuffs. The polarographic technique herein reported was found particularly advantageous where concentration levels in the samples were unknown. The polarography of SOz in acidic solutions was reported by Kolthoff and Miller (5). However, the polarographic wave (6) ] in a for SOn {present in the complex ion [HgClzS0~.]-~ solution of NazHnC1, was obscured by the reduction wave of (6) R. V. Nauman, P. W. West, F. Tron, and G. C. Gaeke, ANAL.
CHEM., 32,1307 (1960).
