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)
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
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0.3 0'3
7 t
0.2
8 z a
m E
s:m a
0.I -
0 0
5
IO
15
20
25
TIME, minutes after SO, addition
n -
2
3
5
4
Figure 3. Absorbance of iron(I1)-ferrozine as a function of time using twice recrystallized ferrozine
6
PH
Figure 1. Absorbance of iron(I1)-ferrozine formed as a function of pH
01
0
I
I
I
0.10
0.20
0.30
ACETATE ION, moles/liter
Figure 2. Absorbance of iron(I1)-ferrozine as a function of total acetate concentration of the ferric salt was brought about by adding concentrated perchloric acid to a small amount of water and gentle heating. Ferrozine, 3-(2-pyridyl)5,6-bis(4-phenyl sulfonic acid)-l,2,4triazine disodium salt was purchased from the Hach Chemical Company. The reagent was grossly impure and had to be recrystallized at least four times from distilled water. A stock solution of approximately 0.008M was prepared from the recrystallized ferrozine. Acetic acid-acetate buffer, p H 3.75 (one molar in acetic acid and in sodium acetate), was prepared from the reagent grade chemicals by neutralizing 1M acetic acid with concentrated sodium hydroxide. Copper sulfate on pumice, 5-8 mesh, was prepared by impregnating evacuated commercially available pumice (Fisher Scientific Company) with aqueous copper sulfate and vacuum drying at 80 "C. This was then packed in a tube 7 X 3 / 4 inches and was used for the absorption of mercaptans and hydrogen sulfide. Procedure. Reagent solutions for the absorption of sulfur dioxide were prepared in 50-ml volumetric flasks by mixing 2.0 ml of acetic acid acetate buffer, 2.0 ml of 0.0025M ferric reagent, 2.0 ml of 0,008M ferrozine, and diluting to volume. A 25.0-ml aliquot of the reagent mixture was added to a gas washing bottle and air or nitrogen containing sulfur dioxide was passed through the solution for a precisely measured period of time. After the addition of sulfur dioxide, the reaction was timed for 20 minutes, and at the end of this period the absorbance was measured at 562 nm using 1.00-cm cells. A standard sulfur dioxide curve was prepared by passing 1516
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
nitrogen or purified air over a calibrated sulfur dioxide permeation tube for varying time intervals. The calibration curve was obtained by plotting the absorbance at 562 nm us. pg of sulfur dioxide (time in minutes x diffusion rate pg/ min). The remaining reagent mixture after taking the aliquot for SO2 determination was used for the blank. With pure ferrozine samples, the blanks remained low and changed rather small amounts on standing, while with impure ferrozine the blanks were in the order of 0.1 absorbance unit and changed appreciably on standing. The unknown amount of sulfur dioxide in atmosphere was determined by passing 50 or 25 liters of air at the rate of 2.2 l./min through the reagent solution and measuring the absorbance after 20 minutes at 562 nm. The amount of bisulfite or sulfur dioxide in water solutions is determined by the addition of aqueous sulfur dioxide solutions to the reagent solution prior to the dilution to volume. Interference of formaldehyde, nitrous and nitric oxides, hydrogen sulfide, and mercaptans was checked by adding small amounts of these substances in the flow stream or directly into the reaction solution. RESULTS AND DISCUSSION
Reduction of iron(I1I) by sulfur dioxide in the presence of ferrozine in acetic acid buffer depends on pH, the concentration of acetate ion, time, and the molar ratios of iron(II1) to ferrozine. The reduction of iron(II1) by sulfur dioxide in the presence of ferrozine is highly dependent on p H as shown in Figure 1. The p H of solution must be controlled between 3.7 and 4.0, quite contrary to the p H dependence of a similar reduction in the presence of 1,lo-phenanthroline. Furthermore, the final acetate ion concentration must be kept in the range of 0.04 and 0.06M as shown in Figure 2. At concentrations of total acetate lower than O.O4M, the p H control is rather poor while a t concentrations higher than 0.06M, the reduction of iron(II1) is incomplete. This is apparently due to the stabilization of iron(II1) by the acetate ion, which is present in approximately a hundredfold excess of iron(II1). The absorbance of iron(I1)-ferrozine chelate depends also on time as shown in Figure 3. The reduction of iron(II1) is over 90% complete within 5 minutes after the addition of SOz; however, after 5 minutes the absorbance continues changing with time. This change primarily depends on the purity of the ferrozine reagent. The change of absorbance of
the development of color. Thus, even impure ferrozine can be used with a reasonable amount of success. The molar ratio of iron(II1) to ferrozine must be maintained close to 1 : 3, at higher concentrations of impure ferrozine blanks become larger and are undesirable. The effect of temperature on the reduction of iron(II1) in the presence of ferrozine by sulfur dioxide is very small in the range from 20 to 45 "C. The absorbance in this range increases by less than lo%, which is quite contrary to the iron(II1)-phenanthroline system. It appears that at room temperature and at 50 "C, sulfur dioxide yields approximately one Fe(I1) per SOz indicating that sulfur dioxide has been oxidized to dithionate, SZO6*- with approximately 95 % efficiency in agreement with the following reaction: ~ C F ~ ( I I I ) A C , I ~ -6~f e r r 2 +2SOZ 2 H z 0+2 F e ( I I ) ( f e r ~ ) ~ - ~Sz062- 2(x)Ac-. 4Hf. Sulfur dioxide in the amounts as low as 3.0 pg and as high as 60 pg have been determined using 1-cm cells as shown in Table I. The relative precision is improved with increasing concentration of SOz; it changes from 4 % at 6.0 pg to 1 % at 15-pg level in the flow system. The negative deviation from Beer's law is observed a t higher SO2 concentrations. This deviation probably results because of the incompleteness of SO2 oxidation by iron(III), evaporation, and mechanical losses while passing the air. Evaporation and mechanical spray a t room temperature is in the order of 2 %. Amounts of formaldehyde, nitric, nitrous oxide, and mercaptans comparable to sulfur dioxide concentration had no apparent effect on the absorbance. Hydrogen sulfide seriously interferes and must be removed; chloride interferes if present in excess of 100 ppm.
Table I. Absorbance as a Function of Sulfur Dioxide Amount of SO?, pg/25 Absorbance at 562 nm for sample ml of final solution less reagent blank From aqueous bisulfite solution at 22 "C (1-cm cell) Observeda Calculatedb Corn. 3.01 6.02 15.05 21.07 30.10 33.11 36.12
0.050 0.101 0.255 0.345 0.480 0.503 0.535
h 0.004 + 0.003 i 0.002 f 0.002 =k 0.003 =t 0.003 f 0.003
0.052 0.105 0.261 0.366 0.522 0.575 0,627
96.2 96.2 97.6 94.2 92.0 87.5 85.2
+
From permeation tube in gas flow system at 22 "C (1-cm cell) 2.75 5.50 6.60 11.00 16.50 22.00 27.50
0.036 =t 0.006 0.090 0.004 0.110 =t 0.004 0.176 i 0.004 0.259 i. 0.004 0.348 i 0.004 0.425 f 0.005
*
0.039 0.096 0.115 0.193 0.289 0.386 0.481
94.8 93.8 95.6 91.2 89.6 89.5 88.5
Absorbancr: was determined on 25 ml of final solution containing 7.5 pmoles of ferrozine, and 1 ml of one molar acetate buffer of pH 3.8. t Calculated values are based on the molar absorptivity of 2.8 X 104M-1cm-1 for iron(II)(ferz)34-complex and the assumption that SO2 is oxidized to dithionate, S2062-. a
2.5 pmoles of iron(",
the blank and the sample of twice and four times recrystallized reagent correspond to approximately 0.025 and 0.008 absorbance unit/hour, respectively. However, if the blank is run side by side with the sample, the difference between the absorbances of the sample and the blank changes by less than 0.006 absorbance unit per hour. The absorbance change may be minimized by the addition of approximately 10 mg of sodium fluoride to the blank and the unknown after
+
+
+
+
RECEIVEDfor review December 30, 1971. Accepted March 30, 1972. Presented at the 161st National Meeting, ACS, Los Angeles, Calif., April 1971. Taken in part from the M.S. Dissertation submitted by Amir Attari to the Graduate School of Loyola University, Chicago, 111.
Ultrasonic Velocity in Water-Deuterium Oxide Mixtures A Basis for Deuterium Determination in Water Solutions J. G . Mathieson and B. E. Conwayl Department of Chemistry, Unioersity of' Ottawa, Ottawa, Canada INPROCESSES FOR ENRICHMENT of water in the deuterium isotope and in control of D content in heavy-water cooled nuclear reactors, it is desirable to have available a facile and direct method for isotopic analysis of H or D content in the water produced or used. Many of the methods available for analysis of protiumdeuterium oxide mixtures have been reviewed by Kirschenbaum (1). The mass spectrometric method is probably the most accurate available for gas phase or vapor samples; however, it involves a heavy financial outlay and requires, for 1
To whom correspondence should be addressed.
(1) I. Kirschenbaum, "Physical Properties and Analysis of Heavy Water," McGraw-Hill, New York, N.Y., 1951.
injection into the spectrometer, the sometimes technically difficult preparation of samples of elemental Hz, Dz, H D gases by exhaustive decomposition of a liquid aqueous medium. The gases, of course, must be representative of the sample and, hence, must not have suffered any change of isotopic composition during their preparation. Conditioning of the mass spectrometer for H / D analyses is usually required, necessitating virtual restriction of the use of the mass spectrometer to H/D analyses only, if reliable and reproducible results are to be obtained. Infrared spectrometry, on the other hand, is best applicable to solutions of either high deuterium or hydrogen content, while specific gravity methods require lengthy temperature equilibration, very accurate weighing procedures and also great care if they are to offer the required accuracy. Similarly, direct thermal conductivity determinaANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
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