8ot L l
! A
t [L
0
w
w
[L
‘h
io
I
I
:0
M O L A R I T Y ACID
I
I
20
l
0 30
6 40
‘MLS. ELUENT
Figure 1. Efficiency of silver elution YS. nitric acid concentration
nal concentrations were 0.2 ppm and below, final analysis was performed by atomic absorption. Above that level, final analysis was performed using the Volhard titration (Table 111). To demonstrate the selectivity of the column for silver, 1 liter of a solution containing 60 ppm copper, 10 ppm nickel, 20 ppm zinc, 0.25 ppm lead, 20 ppm calcium, 0.22 ppm manganese, 0.06 ppm iron, 20 ppm cadmium, and 20 ppm Ag was passed through it a t a flow rate of 3 ml/min. Recoveries for silver averaged 97.0 f 1.1%.Copperfl) and mercury(1) and (11) were the only interferences. No other ions were retained by the column. The ease of oxidation of Cu(1) left only mercury(1) and (11) as interferences. Mercury works its interference in two ways. Mercury(1) will react with the acetylene to the extent that if 250 ml of solution a t a concentration of 500 ppm of mercury(1) is passed through the column, 14% is retained. At the same concentration, mercury(I1) is retained to the extent of 4%. Mercury(I1) under acidic conditions can hydrate the acetylene to the corresponding ketone (12). However, selective reduction or analysis by atomic absorption provides a means of selectively nullifying the interference.
CONCLUSIONS A commercially available, long chain terminal acetylene coated on a solid support has the ability to selectively concentrate and/or separate silver from a variety of cations over a wide range of concentrations. Its advantages (12) M.Kutscherov, Chem. Ber., 14, 1532 (1881).
Figure 2. Elution curve for silver with 8M nitric acid
lie in its ease of preparation and minimum amount of sample handling and treatment. Cationic interferences are minimal and can be excluded with relative ease. Furthermore, a study of the acetylides formed using differential scanning calorimetry demonstrated no safety hazard requiring unusual precautions for the laboratory use of acetylenics as column materials. Considering the recovery of silver, adsorption effects account for silver losses (13, 14). Radiometric methods using lloAg have been used to follow concentration steps and account for silver losses (15). To obtain reproducible results, one must be mindful of adsorption effects which are buffer, container, concentration, time, temperature, and technique dependent. The overall performance of the acetylenic column is comparable with other existing silver concentration techniques (16). With regard to its selectivity, its performance is unchallenged. Received for review April 30, 1973. Accepted October 5 , 1973. This work was supported under Grant PRF 5399AC by the Donors of the Petroleum Research Fund administered by the American Chemical Society. (13) F. K. West, P. W. West, and F. A. Iddings, Anal. Chem., 38, 1566 (1966). (14) R. Woodriff, B. R. Culver, D. Schrader, and A. B. Super, Anal. Chem., 45, 231 (1973). (15) T. Chao,M. Fishrnan, and J. Ball. Anal. Chim. Acta, 47, 189 (1969). (16) /bid., p 190.
Determination of Total Cyanide in the Presence of Palladium George W. Latimer, Jr., L. Ruth Payne, and Marguerite Smith PPG Industries, P. 0.Box 4026, Corpus Christi, Texas 78408
The problem of determining cyanide in the presence of metal ions which form acid-stable, cyano complexes has been dealt with in a number of ways. If the sample is a solid and free from other nitrogen-containing materials, carbon and nitrogen values have been used (1-3), although not always successfully ( 3 ) . Fusion with potassium (1) F. Feigl and G. B. Heisig, J . Amer. Chem. Soc., 73, 5630-5 (1951). (2) W. L. Magnuson, E. Griswald, and J. Kleinberg, lnorg. Chem.. 3, 88-93 (1964). (3) C. J. L. Lock and G. Wilkinson, J. Chem. SOC., 1962, 2281-5.
in a nickel bomb has proved satisfactory for cyano-rhenium complexes ( 3 ) ,but is tedious and cannot be applied directly to aqueous systems. Many acid-stable complexes are analyzed by distilling the cyanide from acidified mercuric magnesium chloride solution or after refluxing the compound with cuprous chloride ( 4 ) ; however, even with such vigorous conditions, recoveries of cyanide from systems containing palladium, mercury, and cobalt range between 4-90% ( 4 ) . (4) C. T. Elly. J. Water Pollut. Contr. Fed.. 40, 848-56 (1968).
A N A L Y T I C A L CHEMISTRY, VOL. 46, NO. 2, FEBRUARY 1974
311
Table I . Effect of Conditions on Recovery of Cyanide from Pd Solutionsa Cyanide reConditions covered, % Run 1
2 3
4
Schulek titration of sample only, /.e., without distillation Mercaptoacetic acid omitted; 2 0 ml H3P04 present during distillation Mercaptoacetic acid present; H2S04 substituted for H 3 P 0 4 Distillation with mercaptoacetic acid and 20 ml H3P04 present
None
Table 11. Analysis of Pd(CN)2 Wt % Pd(CN)2calculated from
determination of Sample description
Mole ratio,
Pd
CN
C
N
Pd/CN
91.2a 93.2b
90.9 94.F
93.4d ...
93.7d . ..
0.501
91.2a
92.lC
93.4d
93.7d
0.495
Commercial Pd (CN)z
10
Lot 1 Lot 2
90
99.5 f 0.6b
Systems contained weighed amounts (approximately 0.1 g each) of Confidence limits (95%)for 5 determinations.
Pd and K C N .
Although this paper describes a procedure for the determination of cyanide in palladium-containing solutions and in palladium cyanide, the method should be applicable to many acid-stable complexes. EXPERIMENTAL Apparatus. The distillation unit was either commercial Kjeldah1 equipment or a simple ground-glass setup equipped with a separatory funnel for adding reagents to the reaction flask. The delivery tubes, containing wads of glass wool saturated with NaOH solution to ensure intimate contact of the first vapors with base, led directly to W - m ! volumetric flasks which served as the HCN absorbers. Reagents and Solutions. Palladium cyanide was either purchased commercially or prepared by reaction between palladium chloride and mercuric cyanide (3). The palladium standard was prepared by dissolving the metal in aqua regia, adding H ~ S O I , and evaporating to fumes of so3. Standard solutions of palladium and cyanide were prepared by adjusting the pH of a solution containing 0.1 gram of Pd to 10 with ammonia and then adding a weighed amount (about 0.13 gram) of cyanide. The scrubbers used to recover the cyanide contained 10 ml of a 2% ZnClz solution (prepared by dissolving the requisite amount of ZnClz in 100 ml of water and adding sodium hydroxide until all the precipitate which formed redissolved) and about 85 ml of water. Procedure. Samples were placed in distillation flasks containing 1 0 0 ml of water. Solid palladium cyanide samples (-0.1 gram) were dissolved by adding sufficient ammonia to give a pH of 10 and heating gently. The solution was transferred to the distillation equipment and 20 ml of and 10 ml of 2% w/v mercaptoacetic acid were added. After thorough mixing, the solution was distilled to the point that the residue began to char. The ZnClz-NaOH scrubber was acidified with 35 ml of 20% phosphoric acid. cyanide oxidized to BrCN by adding Brz water until the solution retained a deep yellow color, the unreacted Brz removed with phenol. and the BrCN determined iodometrically. (The details of the cyanide completion, known as the Schulek titration, can be found in reference 5.)
0.493
Pd (CN) prepared in this
Laboratory
Determined by fusing t h e sample with pyrosulfate. boiling an aliquot with NaCI, and precipitating the nioximate. Determined on residues left
after distilling the cyanide. The range for the two determinations was 0.8%. C T h e range for two determinations was 0.8%. These samples also show 0.61 wt % hydrogen, equivalent to 11 .O% water.
RESULTS AND DISCUSSION The effects of various experimental conditions on the results of analysis of standards are shown in Table I, the analysis of various palladium cyanide materials in Table II. For comparison, Table II shows palladium cyanide purities calculated from carbon and nitrogen values. According to suppliers, commercial Pd(CN)Z products are analyzed by igniting the material and weighing the residue. Palladium cyanide complexes are exceedingly stable; palladium sulfide does not precipitate when diamminodicyano palladium(I1) is treated with ammonium sulfide (I). However, PdS can be precipitated from the corresponding cyanocomplex in acid solution. Since addition of thiourea to acid Pd-CN solutions and of mercaptoacetic acid to either acid or basic solutions turned the colorless solutions yellow and since cyanide could only be distilled in their presence (cf. Table I), the Pd-thiourea (6) and the Pd-mercaptoacetic acid (7) complexes must be more stable than the cyanide complex. Mercaptoacetic acid was selected for use over thiourea because it appears to form a complex stable over a wider pH range and to minimize H2S production from the hydrolysis of the excess complexing agent. The iodometric titration of the evolved cyanide was selected because sulfide-if present-does not interfere. The remainder of the Pd(CN)2 samples appear to be water. The data suggest that these samples were, in actuality, monohydrates. Received for review June 28, 1973. Accepted August 20, 1973. (6) I . L. Bagbanly and B. Z . Rzaev. Azerb. Khim. Zh., 1967, 117-20;
(5) I . M. Kolthoff and R. Belcher, "Volumetric Analysis 111." science, New York. N.Y , 1947, p 303.
312
Inter-
Chern. Abstr.. 67, 90759 (1968). (7) A. T. Pilipenko and N . N . Naslei. Ukr. Khim. Zh.. 33, 730-4 (1967); Chem. Abstr.. 67, 96555s (1967).
ANALYTICAL CHEMISTRY, VOL. 46, NO. 2, FEBRUARY 1974
