Determination of Cyanide in Its Platinum and Palladium Complexes Bernard L. Gilbert, Bert L. Olson, and Wilhad Reuter IBM Thomas J. Watson Research Center, Yorktown Heights, N. Y . 10598
The high toxicity of CN- has generated a widespread interest in analytical methods for its determination in industrial wastes and other waters. Although there exists an extensive relevant literature, none of the published procedures offered a solution to two closely related analytical problems of interest in our laboratory: 1. One of our research groups is interested in the preparation and characterization of Pt(II),(IV) complexes. Such compounds have a columnar structure with mixed oxidation numbers and have strongly anisotropic electrical and magnetic properties ( I ) . Compounds were prepared (2) from solution by coprecipitation of PtIV(CN)4Brz2- in a large excess of Magnus' Salt, [PtII(NH3)4] [PtIIC14]. The concentration of P t I b ' in the product can be determined indirectly from its CN content, provided a reliable analytical method can be developed for the determination of CN strongly complexed by Pt in a large excess of ammonia. 2. In the fabrication of computer elements, some components are electroplated with Pd. Traces of CN- enter the plating bath when the components, which have been previously cleaned in a NaCN solution, are dipped into the bath. Thus, the plating rate of Pd continuously decreases because of the formation of a palladium cyanide complex. For this reason, the CN concentration must be monitored in the plating bath, which also contains a large excess of ammonium salts. Common to both problems is the presence of strongly complexing elements of the Pt group and a high concentration of ammonia. The analysis of CN is considerably complicated by the presence of these two species. Pd(CN)42- is about the most stable cyanide complex, possibly surpassed by Pt(CN)42-, which is "practically not dissociated" (3). The overall stability constant: K , = M(CN),/([M][CN]") as shown in Table I for several metal (M) cyanide complexes covers a range of fifty orders of magnitude. Many workers in this field have recognized the need to break such complexes and to separate CN from the complex-forming metal ion prior to the volumetric or colorimetric determination of the CN content. In agreement with other workers (8-1'4, we have found that most distillation procedures do not yield reasonable recoveries with complexes of high stability. We explored several methods (11-13) as a possible solution to our problem. However, no procedure was found to give satisfactory yields except the F. Mehran and B. A. Scott, to be published. P. S.Gomm and A . E. Underhill, J. Chem. Soc., A , 334 (1972). N . Demassieux and J . Heyrovsky, Bu//. SOC.Chim., 4, 45 (1929) I . Leden, Svensk Kem. Tidskr., 56, 31 (1944). L. H . Jones and R. A . Penneman. J , Chem. Phys., 22,965 (1954). A. E. Martell and M . Calvin, "Chemistry of Metal Chelate Compounds," Prentice-Hall, New York, N.Y.. 1953. R. H . Atkinson and A . R. Raper, J. Hectrodepositors' Tech. Soc., 8, 6 (1933). F. J. Ludzack, W . Allen Moore, and C . C. Ruchhoff. Ana/. Chem.. 26, 1784 (1954). R. Leschbar and H . Schlichting, Fresenius' 2. Anal. Chem.. 245, 300 (1969). F. Hilbert and N . A . Darwish, Fresenius' 2. Anal. Chem., 255, 357 (1971).
Table I. Stability Constants for Metal Cyanides Complex
Log K n
Cd(CN)4'-
18.9 20.7 64 91
A g ( C N )z
~
Co(CN)rj3 Pd(CN)4'-
~
(4)
(5) (6) (7)
Carius sealed tube method (13) using standard KzPt(CN)4. Because of the complication arising from the presence of the large excess of ammonia, this method was abandoned. In the search for a solution to our problem, we finally considered the decomposition of the sample in a flow of hydrogen at an elevated temperature. We developed this idea into an analytical procedure for the quantitative determination of cyanide in the presence of strongly complexing metal ions and large concentrations of ammonium ion. EXPERIMENTAL A p p a r a t u s . The combustion apparatus consists of a "clam shell furnace," fitted with an 18-in. long quartz tube, ll#s-in.0.d. having a female 34/45 standard taper joint for loading the sample and a male 14/35 standard taper joint for connection to the 2 absorption bubblers. Reagents. These are identical with those reported by Epstein ( 1 4 ) for the colorimetric determination of C?j by t h e pyridinepyrazolone technique. Procedure. T h e quartz combustion boat containing a known quantity of the solid or liquid sample is inserted into the center of the quartz tube. For the analysis of the cyanide-bromide platin u m complex, complete recovery of cyanide required t h e addition of several drops of 0.5,V KOH. The hydrogen flow is adjusted to 30-50 cm3/min. HCN is absorbed in two sequentially attached bubblers filled with 40 and 10 ml of 0.21V NaOH. Solutions are first evaporated to dryness at 100 "C in the Hz stream. When the solutions contain large amounts of NH4 salts, the bubblers are preceded by a U-tube filled with glass beads. Heating the tube to about 150 "C during the preliminary evaporation prevents the condensation of water and trapping of cyanide in the U-tube. The temperature is now slowly raised (-30 minutes) to 800 " C . condensing ca. 997~of the ammonium salts in the U-tube. which. in this cycle is externally cooled in an ice bath. The solutions from both bubblers are then combined. and after an appropriate dilution, the cyanide concentration is determined by the pyridinepyrazolone method using Epstein's procedure except for the following modifications, suggested by Kruse and lLlellon ( 2 5 ) . Ten milliliters of M / 1 5 KH2PO*-KazHP04 buffer were added prior to p H adjustment to 6.8 with 0,LV HzS04. After the chloramine-T has reacted to form cyanogen chloride, 15 ml of pgridine-pyrazolone reagent are added. Alternatively. the CN concentration can be determined with a C S ion-specific electrode. We have not however pursued this approach. Traces of S2- present in our a b sorber solution are known to interfere with this method. (11) P. D. Gouden, B. D . Afghan, and P Brooksbank, Anal. Chem.. 44, 1845 (1972). (12) E. Heintz. lnorg. Synth.. 7, 142 (1963). (13) B. Jaselskis and J. G . Lanese. Anal. Chim. Acta. 23, 6 (1960). (14) J . Epstein, Ana/. Chem.. 19, 272 (1947). (15) J . M . Kruseand M . G . Mellon, Anal. Chem.. 25, 446 (1953)
RESULTS AND DISCUSSION The accuracy of this method was tested with K2Pt(CN)4.3H20, purchased from the Varlacoid Chemical Co. Its stoichiometry was verified by Pt and K analyses. Ten CN analyses were made on samples in the range from 65 to 1200 wg using the hydrogen reduction technique. Recoveries of 99 f 4% (STD) were obtained. NH3 present in excess of 50 pg/ml in the final test solution decreases the absorbance of the CN color complex. The NH3 content can be held below this critical level by means of the U-tube trap cooled with ice water as described above. Alternatively, the NH3 content in the absorber solution can be readily determined with Nessler's reagent. Equivalent amounts of ammonia are then added to the standard solutions. Once we recognized this inter-
ference problem, recoveries have been excellent. Kine separate determinations of 43 pg of CN in the presence of a 100-fold excess of Pd and NH3 gave an average recovery of 101 f 5% (STD). Similar to "3, bromide was found to quench the color complex when present in excess of 2 pg/ml in the final test solution. Since some of the Pt compounds of interest to us contained bromide, we subjected the combined absorber solutions to a Serfass distillation (16). The cyanide concentration was then determined in the distillate with excellent yields. Received for review June 6, 1973. Accepted August 6, 1973. (16) E. J Serfass, Platmg, 39, 267 (1952)
Data Reconstruction Techniques for the Technicon AutoAnalyzer R. D. Begg Department of Mechanical Engineering, University of Glasgow, Glasgow, G 12 800, U . K .
The problem of increasing the sample rate through Technicon AutoAnalyzers is still acute in fields where the volume of chemical monitoring is increasing faster than the facilities available. Almost all steps taken to increase throughput, such as smaller sample volumes and higher fluid velocities, result in a degradation of the information contained on the output record, that is on the final graph of concentration distribution along each line of sample segments. To counteract this, some attention has been focused on methods of compensating the output information for the distortion caused by the characteristics of continuous flow analytical methods. In a short paper ( I ) , Walker has demonstrated the benefit of applying a 1st order data reconstruction technique to improve the definition of the output from an AutoAnalyzer. Since then, analog data processing circuits have been developed and tested (2, 3) which carry out this operation before the graphical output. Justification for this technique was based on a very much oversimplified set of equations for the AutoAnalyzer, which equations have now been superseded by a more accurate linear dynamic model ( 4 , 5). By consideration of this new model, it is possible to show why the technique produces acceptable results and to calculate a theoretical value for the coefficient used in the process. Hitherto, the value has been found experimentally. (1) W. H. C. Walker, Clin. Chim. A c t a , 32,305 (1971). (2) W. H. C. Walker, J. Townsend, and P. M. Keane, Clin. Chim. A c t a , 32, 119 (1972). (3) A. Fleck, J. E. Carlyle, and A . S. McLelland, Clin. Chim. Acta, in press. (4) R. D. Begg, A n a l . Chem., 43,854 (1971). ( 5 ) R. E. Thiers. A . H . Reed, and K . Delander, Ciin. Chem., 17 ( l ) , 42 (1971).
ANALYSIS
Walker's Method. The basis of Walker's reconstruction technique is the assumption that the variation of concentration along the sample is governed by a first order equation, which is
E
=
h
+ b(dy/dtj
(1)
where E is the final value of concentration (after many segments or slugs), h is the value of concentration a t any point along the sample, dyldt is the gradient of the concentration curve a t the point, and b is a constant. The reconstruction technique consists of selecting points outlining the curve of concentration us. length along the sample which is the normal form of the AutoAnalyzer output. To the ordinate a t each point is added an amount equal to a constant times the gradient of the curve a t that point. If the constant is satisfactorily chosen, the locus of the amended ordinates provides a much improved definition of concentration maxima without altering their value. It has been shown (3, 4 ) that the variation of concentration along any sample in an AutoAnalyzer tube can be adequately represented by the expression
+
which defines the concentration of the ( n 1)th slug along the sample in the tube in terms of the length of tube traversed (1) and the leakage (carry-over) length constant associated with the particular analytical process ( A ) . In this notation, Walker's equation 1can be written
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