Table VII. Analysis of Gold Solutions in the Presence of Large Amounts of Base Metals Sample Relative absorbance 0.1013 Pure standard 5 ppb gold solution 0.0947 2.0% Fe(II1) 5 ppb Au 0.0996 2.5% Ni(I1) 5 ppb Au 0.0980 4.0% Cu(I1) 5 ppb Au 1% Fe(II1) 1% Ni(I1) 1% 0.0964 Cu(I1) 5 ppb Au
+
+ -+ + +
+
gold without interferences from samples containing as high as 100 ppm of complexed mercury. Cyanide solutions also interfere with the chelation procedure ; however, this interference can be obviated by first oxidizing the solution with potassium permanganate-hydrochloric acid solution. The polyschiff base column provides an effective means of
concentrating ionic and colloidal gold from natural water samples. The use of atomic absorption spectrometry, combined with the chelation procedures used here permits the detection limit of this method to be 0.5 ppb/liter of sample. It is possible to lower the detection limit to considerably smaller values by passing the appropriate amount of sample through the column. Because the concentration procedure and measurement of the gold are completely independent from each other, techniques other than atomic absorption spectrometry could be applied as a means of measurement. Such a procedure using a colorimetric end point is presently being investigated. RECEIVED for review May 8, 1969. Accepted August 11, 1969. Investigation supported in part by a grant AP 00308-06 of the National Air Pollution Control Administration, Public Health Service and from an endowment by the Robert A. Welch Foundation.
Activity Measurements in Concentrated Sodium Chloride-Potassi um Chloride Electrolytes Using Cation-Sensitive Glass Electrodes Rima Huston and James N. Butler Tyco Laboratories, Inc., Waltham, Mass. 02154 ELECTRODES made from sodium aluminum silicate and lithium aluminum silicate glasses are well known to be selective for sodium in the presence of other cations, particularly H+and K+. This selectivity and thermodynamic reversibility is well documented in dilute solution ( I ) , as well as in concentrated solutions containing a single salt component (2). Relatively concentrated multicomponent solutions have been studied by means of cells such as ( 3 , 4 ) Ag/AgCl/Na+, C1-, X/glass electrode where X i s a cation or anion which does not interfere with the operation of either the Ag/AgCl or glass electrode. Such data have been verified (for X = Mgz+,Ca2+,and S042-) by measurements with amalgam electrode cells such as (5-7) Ag/AgCl/Na+, C1-, X/Na(Hg) and (for X = MgZ+,Ca2+,Ba2+,SO4+, NO3-, and CIOa-) by isopiestic measurements (7,8). Although considerable attention has been paid to analytical measurements of sodium ion activity in solutions containing potassium ion ( I , 9, IO), verification of the selectivity of these (1) “Glass Electrodes for Hydrogen and Other Cations,” G .
Eisenman, Ed., Marcel Dekker, New York, 1967. (And references cited therein. See especially pp 280-2). (2) A. H. Truesdell, Science, 161, 884 (1968). (3) R. D. Lanier, J . Phys. Chem., 69, 3992 (1965). (4) J. C. Synnott and J . N. Butler, ibid., 72, 2474 (1968). ( 5 ) J. N. Butler, P. T. Hsu, and J. C. Synnott, ibid., 71,910 (1967). (6) J. N. Butler and R. Huston, ibid., 71,4479 (1967). (7) J. N. Butler, Res. Develop. Progr. Rept., 388, Office of Saline Water (1968). (8) R. M. Rush, U. S. At. Energy Comm. Rept., ORNL-4402 (1969). (9) E. W. Moore and J. W. Ross, Science, 148,71 (1965). (10) E. W. Moore, Ann. N . Y.Acad. Sci., 148, 93 (1968).
glass electrodes has generally been done in dilute solutions for two reasons: First, the activity coefficients of the two ions can be calculated from the Debye-Huckel theory for ionic strengths less than O.lm, and are essentially equal in this region. Second, most analytical measurements are made with a reference electrode employing a saturated KC1 salt bridge, and the potential of this liquid junction cannot be assumed constant if the test solution is much more concentrated than O.lm. Neither of these objections applies to the cell without liquid junction which we have studied: Ag/AgCl/Na+, K+, C1-/glass electrode If the glass electrode responded only to sodium ion and not at all to potassium ion, the potential of this cell would give directly the activity coefficient y I 2of NaCl in the mixed electrolyte:
The temperature (T), Faraday Constant ( F ) and Gas Constant (R)as well as the molal concentration of sodium (mXa) and chloride ( m o ) ions in the electrolyte are known accurately. The standard potential Eo is determined by calibrating the glass electrode in an electrolyte containing only NaCl at known concentration, where the activity coefficients are known
(IO A few measurements of this cell at ionic strength l m were reported by Lanier (12), but the electrode he used (Beckman 39137) was made with a glass (NAS-27-5) which shows es(11) R. A. Robinson and R. H. Stokes, “Electrolyte Solutions,”
Butterworth & Co., Ltd., London, 1959, Appendix 8.10. (12) R. D. Lanier, J . Phys. Chem., 69,2697 (1965). VOL. 41, NO. 12, OCTOBER 1969
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Table I. Activity Coefficients of NaCl in NaCI-KCI Electrolytes at 25 OC Total ionic strength
XI(NaCl)
AE, mV
0.4805 0.4834 0.4876 0.4911 0.4952 0.4983
1.oooO 0.8564 0.6585 0.4722 0.2706 0.1145
0 2.25 10.7 18.4 31.7 53.4
0.4805 0.4834 0.4876 0.4911 0.4952 0.4983
1.000 0.8564 0.6585 0.4722 0.2706 0.1145
0 3.1 11.3 19.0 33.4 54.9
0.9323 0.9466 0.9548 0.9703 1,0554 1.0554 1.0554
1 .m 0.7030 0.5329 0.2111 0.0108 0.00137
