P
Table I. Determination of Hydrogen Sulfide in Water Concentration of Recovery shown by 9 from hydrogen sulfide 12 results, in water, Procedure Pg/l. 96 =k 2 la 20-200 95 + 2 lb 20-200 97 3 2 8-80 98 i 6 3 0.1-0.5
I
2
z
/I
I /
30
ml Z.IO*N
TMF
Figure 1. Fluorimetric titration of hydrogen sulfide as triethyllead sulfide with tetramercurated fluorescein in hexanol-ethanol mixture 1. Added 0, found 0 H S ; 2. Added 0.0514, found 0.0510 p g HzS; 3. Added 0.120, found 0.119 pg HzS
as indicator to the red color. Consumption of H M B for indicator should be ca. 0.03 ml. Multiply the result by 1.13. Procedure 3. (Above 0.01 gg/l. of H2S.) Shake 500 ml of water containing 0.5 ml of solution A with 10 ml of 0.01 triethyllead chloride in hexanol, add to 3.5 ml of the extract obtained 0.5 ml of solution B and titrate with 2.lO-SN alcoholic solution of TME;, recording the total fluorescence a t 520 n m of exciting wave. The end point of the titration is estimated as a point of intersection of two straight lines as shown in Figure 1. (Fluorimeter “Spekol,” test tube, 17m m diameter.) Multiply the result by 1.80. The decrease of sulfide as triethyllead sulfide content in hexanol amounts t o ca. 2 per day.
The analytical characteristic of the suggested procedures is demonstrated in Table I. The solubility of n-hexanol in water a t 20 “C, as found from the increase of concentration of triethyllead sulfide after shaking with a known volume of water amounted to 7.4 ml in 1 liter. Consequently taking V liters of water, L’] ml of hexanol, and u2 ml of the extract obtained for analysis, the result multiplied by (VI - 7.4 V)/uzcorresponds to hydrogen sulfide content in V liters of water. For V = 0.5, ul = 15, and u2 = 10, the above coefficient amounts t o 1.13; and for V = 0.5, u1 = 10, and 02 = 3.5, it amounts to 1.80. There are no interferences from common ions in water. For fluorimetric titration, any suspension in hexanol should be removed by paper filtration. Thiols, cyanide, xanthate, and dithiocarbamate d o not change the end point of the fluorimetric titration. The sum of thiols and sulfide is obtained by Procedures l a , l b , and 2, the thiols can be removed in a n aliquot by acrylonitryle (14). Hydrogen cyanide can be removed by formaldehyde (15).
RECEIVED for review June 24, 1970. Accepted December 16, 1970. (14) M. Wrohki, Analyst, 85, 526 (1960); Acta Chiin. Acad. Sei. Hung., 28,303 (1961). (15) M. Wrohski, Analyst, 84, 668 (1959); C/zr/n.Anal. (Warsaw), 5, 293 (1960).
Simultaneous Coulometric Determination of Silver, Cadmium, and Indium in Ternary Alloys Albert0 Borello and Guido R. Guidotti Industrial Chemical Laboratory, CNEN-CSN-Casaccia-Rome, Italy POLAROGRAPHIC AND COULOMETRIC investigations o n silver, cadmium and indium singly have been very extensive. However, no procedure exists for the determination of these elements simultaneously. Because they can occur together in ternary alloys of nuclear interest, a n analysis is necessary. It is the aim of this paper to demonstrate the possibility of performing the simultaneous analysis of Ag, Cd, and In in such a way as to avoid the mutual interference of I n and Cd. I n practice, combinations of the more common individual Procedures were found not to work especially, owing to the mutual interference of I n and C d ; difficulties arose from I n particularly because of its very slow reduction at a H g electrode in acid media useful for Cd and Ag. Such difficulties were Overcome by choosing a supporting electrolyte in which Cd, In, and Ag could be reduced sepa-
rately. HCIO, is useful for a fast, reversible reduction a t a H g electrode of Ag and Cd, whereas the totally irreversible polarographic reduction of I n is converted to a reversible, diffusion controlled process by the presence of ligands such as the halides which accelerate the normally slow reduction of aquoindium ions (Z-5). The entire reduction wave is shifted (1) I. M. Kolthoff and J. J. Lingane, “Polarography,” 2nd ed., vol. 11, Interscience, New York, N. Y., 1952. (2) CHEM.. , , E. D. Moorhead and W. W. McNevin. ANAL. , 34. , 269 (1962). (3) A. J. Engel, J. Lawson, and D. A. Aikens, ibid., 37, 203 (1965). (4) D. Cozzi and S. Vivarelli, Rend. Soc. Mineral. Ira/., 10, 359 (1954). (5) H.F., Walton, “Chemical Analysis,” Prentice-Hall, Englewood Cliffs, N. J., 1962.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
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toward more positive potentials at the same time, avoiding interferences by the medium discharge. After reducing Ag and C d in HC104, N a I was added t o the electrolyzed solution and a ligand catalyzed controlled potential coulometric reduction of In was carried out successfully. EXPERIMENTAL Apparatus. A n O R N L Model Q-2005 controlled potential coulometric titrator coupled with a D M Model 2001 digital voltmeter as a readout instrument was employed for all coulometric studies. A mechanically stirred H g pool cathode was employed in a conventional coulometric cell. A Pt wire (0.4-mm diameter) counter electrode and a Radiometer Model K-4112 saturated calomel reference electrode were used. An Atlas Werke Tast Polarograph was employed for all polarographic studies dealing with In and Cd. The auxiliary apparatus (cell, electrodes, and gas train) was conventional. The D M E had a drop time in 1N HC104 of 4.0 sec, and the mass flow rate was 2.2 mg/sec at a H g height of 58 cm with an applied potential of -0.60 V. Reagents. All chemicals used were reagent grade. The metal standards used were 99.99% assay (Fluka A G Chemische Fabrik). Procedure. DISSOLUTION OF SOLIDSAMPLES. A weighted portion of the metals was dissolved in a minimum of 1 :1 HNOI and diluted to volume with deionized water in a volumetric flask. Care was taken that p H was sufficiently low (less than 5) to prevent hydrolysis of In (5). PREPARATION OF TESTPORTION FOR ANALYSIS.An aliquot from the resulting sample solution containing approximately 3 mg of In, 1 mg of Cd, and 20 mg of Ag was added into the electrolytic cell containing about 10 cc of triply-distilled H g and 40 cc of 1N HClOi as a supporting electrolyte. COULOMETRIC ANALYSIS. Before adding the sample to be analyzed, the solution was sparged 5 min with On-free N?. Then pre-electrolysis was carried out at -0.64 V cs. SCE until the current decreased to 0.04 mA (time required is about 15 min). The N P flow was maintained during the following reduction steps. Ag(1) was first reduced to Ag(Hg) at +O.O V us. SCE until the current decreased to 0.04 mA. The integrated current consumed during the coulometric reduction was read as an electric tension with the digital voltmeter and the amount of Ag was calculated cia Faraday’s law (n = 1). Then the integrator was zeroed. Cd(I1) was then reduced to Cd(Hg) a t -0.63 V, GS. SCE until the current decreased to 0.04 mA. The integrated current was read as before and Faraday’s law (n = 2) was used to calculate the amount of Cd. Then the integrator was zeroed again. A calculated volume of 1 N NaI solution was added to the electrolytic cell in order to have a 10-12:l molar ratio I-/In. A waiting time of 5 min was sufficient for complexing In. Then the reduction of In(II1) to In(Hg) was carried out by electrolyzing at -0.615 V cs. SCE until the current decreased to 0.04 mA. The amount of I n was calculated as before L;ia Faraday’s law (n = 3). I n all calculations, a correction is made for the background current which is reached at 0.04 mA within 15 min; the values for the background correction were obtained by electrolyzing 40 cc of 1N HCIOl at i 0.0 V and -0.63 V for Ag(1) and Cd(II), respectively, and by electrolyzing 40 cc of 1 N HClOd 0.3 cc of 1 N N a I at -0.615 V for In(II1).
+
Ag, mg Cd, mg In, mg Added Found Added Found Added Found 1.08 1.075 1.12 1.115 1.15 1.16 10.98 10.99 2.81 2.80 5.74 5.73 21.94 21.91 3.375 3.38 11.69 11.68 a Tabulated values average of 4 determinations (after correction for the background current). Table 11. Controlled Potential Coulometric Determination of Ag, Cd, and In in Synthetic Ternary Mixture According to Procedure Given in Text.
z
z
Ag, Cd, In, 72 Added Found Added Found Added Found 1 72.62 72.61 5.74 5.73 21.64 21.76 80.02 5.12 5.10 14.90 14.81 2 79.98 14.85 14.76 5.12 5.11 3 80.03 80.07 4 79.98 79.96 5.05 5.06 14.97 14.99 79.96 5.05 5.03 14.97 15.09 5 79.98 Tabulated values average of 4 determinations (after correction for the background current). Run No.
Table 111. Controlled Potential Coulometric Determination of Ag, Cd, and In in Ternary Alloys Obtained by Fusion According to Procedure Given in Texta Sample No. Ag, Z Cd, Z In, 5.18 f 0.01 14.50 f 0.04 1 80.4 i 0.1 14.97 i 0.03 5.22 f 0.02 2 79.9 f 0.1 a Tabulated values average of 4 analyses.
z
80% Ag, 15% In, 5 % Cd ternary alloy which is used as a n absorbent material in the stainless steel jacketed control rods of the ROSPO reactor a t Casaccia Nuclear Studies Center (6). Interferences. N o effort was made to study either cationic o r anionic interferences owing to the purity of the starting material. The total content of impurities in the samples to be examined was -360 ppm. The maximum concentration of interfering impurities, namely Cu(II), Tl(I), Pb(II), Fe(III), and Bi(III), can give a maximum error of the order of ~1 part per thousand. Tests were made in the presence of H N 0 3 employed as dissolving agent; chloride was absent a t the end of the dissolution step and no catalytic wave was observed in the reduction of In(II1) at the D M E . Concentrations as low as 0.05M were found to interfere slightly, giving greater results. To achieve the best results, it is necessary to analyze samples after removing nitrate ions by fuming with perchloric acid. In this way, some chloride was observed, resulting in a polarographic catalytic wave starting at -0.65 V cs. SCE, that is after the complete reduction of Cd(I1) in the same conditions. Consequently, no interference results in the reduction of Cd(I1) when in the presence of In(II1). ACKNOWLEDGMENT
RESULTS
Tables I and I1 present some results obtained for the coulometric determination of Ag, Cd, and I n singly and in synthetic mixture as described in the procedure. Electrolysis time for reduction of each ion was generally shorter than 15 min for Cd(I1) and Ag(1) and shorter than 35 min for In(II1). Table I11 presents some results obtained in the analysis of 608
Table I. Controlled Potential Coulometric Determination of Ag, Cd, and In Standard Solutions According to Procedure Given in T e x e
ANALYTICAL CHEMISTRY, VOL. 43, NO. 4, APRIL 1971
The authors are very grateful to Mr. G. Pigozzi who has contributed to the experimental work. RECEIVEDfor review July 1, 1970. Accepted Octobzr 26, 1970. (6) A. Villani, et a/., Nofiziario, 15, 12, 1969, 35-51, Comitato Nazionale Energia Nucleare ed., Roma, Italy.
