determination of trace levels of gold(i) as its cyano complex by ion-interaction reversed-phase...

536 Anal. Chem. 1900, 60, 536-540

Determination of Trace Levels of Gold(1) as Its Cyano Complex by Ion- Interaction Reversed-Phase Liquid Chromatography with On-Line Sample Preconcentration

Paul R. Haddad* and Natalie E. Rochester

Department of Analytical Chemistry, University of New South Wales, P.O. Box 1, Kensington, New South Wales 2033, Australia

Hlghperformance llqukl chromatography Is applied to the determlnatlon of gold( I ) cyanide uslng on-line sample preconcentration. The complex Is resolved by ion-interactlon chromatography on a C18 column uslng a mobile phase of 3268 acetonitrile-water contalning 5 mM tetrabutylammonh Ion, with detectlon by UV absorptlon at 214 nm. Samples are preconcentrated by passage through a C18 precolumn previously condltloned with the above m M e phase. The cholce of Ion-lnferactlon reagent is discussed In terms of the Ionic retentlve capacity of the precolumn and the llnear range of the calibration plot. Under optimal condltlons quantitative blnding of aurocyanide was observed for sample volumes of up to 3 mL, giving a detectlon llmH of 0.43 ppb gold. The preclslon of the method at the 10 ppb gold level was 0.9% relatlve standard devlatlon. The chromatographic condltlons employed are shown to be suitable for the simultaneous determination of ultratrace levels of the cyano complexes of Au( I) , Pd( I I) , and pt( I I ) In solutlons contalnlng high concentrations of free cyanide ion.

In an economic climate where the price of precious metals is high, it becomes feasible to process even very low grade ores. This in turn produces a demand for accurate analytical procedures for these elements which are applicable to trace and ultratrace concentrations. In gold-processing plants and in geological exploration, it is often necessary to analyze solutions containing precious metals in the 1-10 ppb range.

For many years, spectroscopic and electrochemical methods have proved successful for the analysis of precious metals, especially gold ( I ) . Apart from the traditional fire-assay method, atomic absorption spectroscopy (AAS) has been the most widely used method. Flame AAS is suited to the determination of gold a t levels of approximately l ppm and higher, whereas graphite furnace AAS is applicable to much lower concentrations. When analyses in the low parts per billion range are required, it is generally necessary to pre- concentrate the sample by solvent extraction, typically using a liquid ion-exchanger in MIBK as the extracting solvent (2 , 3 ) . Other analytical techniques for gold such as inductively coupled plasma atomic emission spectrometry ( 4 ) , electroan- alysis ( 5 ) , X-ray fluorescence (6), and neutron activation analysis (7) either have insufficient sensitivity for ultratrace applications or are very time-consuming.

In a recent report (8), we have described a chromatographic method for the determination of Cu(I), Ag(I), Fe(II), Co(II), Fe(III), Au(I), Pd(II), and Pt(I1) as their cyano complexes. In this method, the metal complexes were separated by ion- interaction chromatography (IIC) using either a C18 or CN stationary phase and an eluent containing acetonitrile-water and an appropriate ion-interaction reagent (IIR). Detection was achieved by UV absorption a t 214 nm, giving a detection limit of 0.26 ppm for gold. While separation of the above eight

metal complexes required a relatively long time (up to 35 min), the main advantages of the method were that several metals could be determined simultaneously, the eluent was noncor- rosive, and the method was suited to use with conventional reversed-phase columns. Previously published procedures for the separation of metal cyano or chloro complexes by ion exchange have employed corrosive eluents such as perchloric acid (9), sodium chloride ( lo) , and hydrochloric acid ( I O ) , requiring the use of specially designed hardware in which all solvent-wetted parts were constructed of noncorroding ma- terials.

In this paper we describe the application of the above chromatographic method to the determination of gold(1) cyanide in the ultratrace range. Chromatographic conditions are optimized and an on-line sample preconcentration step using a precolumn is incorporated. The method is shown to be suitable for the simultaneous determination of the cyano complexes of gold(I), palladium(II), and platinum(I1).

EXPERIMENTAL SECTION Instrumentation. The liquid chromatograph consisted of a

Waters (Milford, MA) Model U6K injector, Model M590 pro- grammable pump, Model 441 UV absorbance detector operated at 214 nm, and a M730 data module. Samples were loaded onto the precolumn using either a Waters M45 pump or an Eldex (Menlo Park, CA) Model A-30-S single-piston pump. The eluent flow direction was controlled by a Rheodyne (Cotati, CA) Model 7000 six-port high-pressure switching valve which was operated either manually or electronically through the pump microprocessor and an appropriate events unit.

The analytical column was a Waters Nova-PAK C18 column (150 X 3.9 mm i.d.) and the precolumn used for sample preconcentration was a Waters C18 Guard-PAK (5.0 X 6.0 mm i.d.) housed in a Waters Guard-PAK precolumn module. The nitrate determinations required for the evaluation of equilibrium ionic retentive capacities of the concentrator columns were performed by use of a Waters IC Pak A ion chromatography column (50 X 4.6 mm i.d.) with UV detection at 214 nm.

Reagents. The mobile phases used for ion-interaction separations comprised water treated with a Millipore (Bedford, MA) Milli-Q water purification system, acetonitrile (Waters chromatographic grade, UV cut-off 190 nm), and an IIR. For the latter reagent, Waters Low UV PIC A and PIC A and tetraethylammonium chloride (Sigma Chemicals Co.) were used.

Mobile phases were prepared by diluting the appropriate amount of acetonitrile with water, adding the IIR to give a final concentration of 0.005 M, and then diluting to 1 L in a volumetric flask. The resulting solution was filtered through a 0.45-fim membrane filter and degassed in an ultrasonic bath before use.

The ion exchange mobile phase used for the determination of nitrate in the ionic retentive capacity studies contained 25 mM methane sulfonate at pH 7.4, prepared by diluting 2.4 g of methane sulfonic acid (Tokyo Chemical Industries, Tokyo, Japan) to YO0 mL with water in a I-L volumetric flask, adjusting the pH of the solution by the dropwise addition of 1.0 M lithium hydroxide, and finally diluting to volume. The pH was measured with an Activon Model 101 pH meter (Activon Scientific Products, Sydney, Australia).

0003-2700/88/0360-0536$0 1 S O / O CZ 1988 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 60, NO. 6, MARCH 15, 1988 537

Stock solutions of cyano complexes were prepared by dissolution of an accurately weighed amount of salt in 100 or lo00 ppm KCN solution adjusted to pH 9 with 0.1 M NaOH, followed by dilution as required. Analytical grade potassium aurocyanide, KAu(CNI2, was obtained from Fluka AG (Swtizerland), and potassium tet- racyanoplatinate(I1) trihydrate, K2Pt(CN),.3H20, and potassium tetracyanopalladate(I1) trihydrate, K2Pd(CN),.3H20, were syn- thesized as described below.

Throughout this paper, the concentrations of standard solutions (expressed as parts per million or parts per billion) or absolute amounts (micrograms or nanograms) refer to the amount of metal present, rather than to amounts of cyano complexes.

Synthesis of Cyano Complexes. Potassium Tetracyano- platinate(ZZ) Trihydrate. A solution of potassium hexachloro- platinate(1V) was stirred vigorously on a steam bath while a hot solution of hydrazine sulfate (WARNING: this reagent is highly toxic) was added over a period of 15 min. The mixture was stirred on the steam bath for a further 30 min and then filtered to remove any undissolved K2PtC&. The filtrate was then concentrated and cooled to precipitate K2PtC14, which was then added to a cold, saturated solution of KCN, and the K2Pt(CN)4.3H20 salt filtered off and dried a t 110 "C.

Potassium Tetracyanopalladate(ZZ) Monohydrate. Palladi- um(I1) chloride was dissolved in warm water containing a few drops of hydrochloric acid. A solution of the equivalent amount of KCN was added dropwise to precipitate yellow palladium(I1) cyanide. The gelatinous precipitate was collected on a Buchner funnel, washed well with water, and dissolved in a solution of the equivalent number of moles of KCN. After filtration, the solution was evaporated to induce crystallization. The salt was recrys- tallized from water and dried a t 110 "C.

Chromatographic Procedures. General Procedure. All chromatographic separations were carried out at room temperature using a mobile phase flow rate of 1.0 mL/min. Various flow rates were used to load the sample onto the concentrator column during preconcentration determinations.

The analytical and concentrator columns were equilibrated with 60 mL of eluent. Equilibration was established when a steady base line was observed and retention of a standard solution was reproducible. For the equilibrium of the precolumns alone, a volume of only 30 mL of eluent was required.

Sample Preconcentration. Preconcentration of samples was carried out using a standard switching valve configuration (IO), with a flow paths varied according to the following sequence:

(a) Equilibration of the Columns. With both the analytical column and concentrator column in the eluent flow path, 5 mL of eluent was pumped through the system a t 1 mL/min.

(b) Loading Sample onto the Concentrator Column. The auxiliary pump was primed with sample and 10 mL was pumped through the flow lines to eliminate contamination from previous solutions. The swtiching valve was then rotated to place the concentrator column in line with the concentrator pump, while the analytical column remained in the eluent flow path. When the Eldex pump was used as the concentrator pump, the sample volume loaded was determined by measuring the volume of effluent from the concentrator waste line. With the Waters concentrator pump, a fixed flow rate was used and specified volumes were pumped through the concentrator column by varying the pumping time.

(c) Elution of Sample from the Concentrator Column. The switching valve was rotated to the position used in (a) above and the solutes were eluted from the concentrator column and carried to the analytical column for subsequent separation.

Measurement of Ionic Retentive Capacity. The ability of the precolumn to retain ions (defined in this paper as the "ionic retentive capacity") was determined under equilibrium and dynamic conditions. In the equilibrium method the concentrator column was conditioned with a mobile phase containing the desired concentrations of acetonitrile and IIR. A solution of sodium nitrate (5 mM, 100 mL) was then pumped through the concentrator column at 1 mL/min to equilibrate the column with excess nitrate ion. The interstitial nitrate was removed by pumping 250 pL of distilled water through the concentrator column a t 0.2 mL/min, and the bound nitrate was then quantitatively displaced by passing 20 mL of an 8 mM solution of sodium sulfate through the column using a flow rate of 1 mL/min. The column effluent

I I I I I

0 2 L 6 8 Time (minl

Figure 1. Optimized chromatogram for the determination of aurocyanide by direct injection; sample, 25 pL of a 20 ppm (as Au) aurocyanide in 100 ppm cyanide.

Table I. Retention Behavior and Detection Limits for Precious Metal Cyano Complexes under Different Mobile Phase Conditions

cyano retention time, min detection limit, ppb complex 23% ACN 32% ACN 23% ACN 32% ACN

Au(I) 25.2 7.0 260 40

Pt(I1) 34.1 5.5 94 15 Pd(I1) 29.3 6.0 124 19

was collected in a 25-mL volumetric flask and diluted to volume with distilled water. The nitrate content of this solution was then determined by ion chromatography using the conditions specified above. The equilibrium ionic retentive capacity of the concentrator column was equated to the number of microequivalents of nitrate found in the final solution.

The dynamic or effective ionic retentive capacity was determined by initially equilibrating the concentrator column with a mobile phase containing the desired concentrations of acetonitrile and IIR. The detector absorbance signal was zeroed and a gold(1) cyanide standard solution (5 ppm in 30 ppm cyanide) pumped through the concentrator column at 1 mL/min with the effluent being passed through the UV detector. The absorbance signal was monitored until complete breakthrough of the gold(1) had occurred, as indicated by the attainment of a plateau in the absorbance signal. The breakthrough point was considered to be when the absorbance reached 5% of its plateau value, and the effective ionic retentive capacity was then calculated in microequivalents.

RESULTS AND DISCUSSION Optimization of the Direct Injection Method. Before

proceeding with the sample preconcentration approach, the existing direct injection ion-interaction method (8) was modified to maximize the sensitivity for Au(I), Pd(II), and Pt(I1). The chromatographic conditions previously reported (23:77 (v/v) acetonitrile-water containing 5 mM Low UV PIC A) had been selected to achieve the resolution of eight metal cyano complexes and under these conditions the above precious metals eluted late in the chromatogram and suffered from poor peak shape. The mobile phase composition was therefore altered to 32:68 (v/v) acetonitrile-water containing 5 m M Low UV PIC A to achieve more rapid elution of the precious metals. Figure 1 shows a chromatogram for gold(1) cyanide obtained under these conditions and Table I shows retention times and detection limits (determined at a signal to noise ratio of 3 for a 25-pL injection) for both the 23% and 32% acetonitrile mobile phases.

From Table I it can be seen that the detection limits showed the expected decrease corresponding to earlier elution and

538 ANALYTICAL CHEMISTRY, VOL. 60, NO. 6, MARCH 15, 1988

Table 11. Comparison of Equilibrium and Effective Ionic Retentive Capacities of Reversed-Phase Precolumns Conditioned with 5 mM Low UV PIC A in Varying Percentages of Acetonitrilea

equilibrium acetonitrile, 7' effective IRC, pequiv IRC, pequiv

5 0.088 0.81 15 0.074 0.70 25 0.048 0.64

Values shown are the average of triplicate determinations.

that, even in the stronger mobile phase, resolution of the three precious metal cyano complexes was possible. It is interesting to note that the change in elution order of the aurocyanide complex in the two mobile phases: we have noted previously (8) that the relative retention times of Au(I), Pd(II), and Pt(I1) were strongly dependent on mobile phase composition. Under optimal conditions, a plot of peak area versus concentration was linear up to 10 ppm of each of the above precious metals.

Preconcentration Using IIC. Trace enrichment using a concentrator column to trap solutes from a large sample volume is a suitable method for the analysis of ions (11-13) and the concentrator column is usually packed with an appropriate ion exchange material. Band broadening in t& system is minimized if the solute ions are back flushed from the concentrator column; that is, they are eluted in the reverse flow direction to that in which they were loaded.

Column preconcentration has been used extensively and successfully with precolumns having chemically bound ion- exchange functionalities but has found limited application to IIC. IIC is a modified reversed-phase liquid chromatographic technique for ionized solutes which involves the addition to the mobile phase of a hydrophobic ion, called the IIR, which has a charge opposite to that of the solute ion. Adsorption of the IIR onto the column surface results in the formation of an ion exchanger ( 1 4 , 1 5 ) and this leads to an increase in retention of the solute ion. When IIC is employed to convert a reversed-phase precolumn into an ion exchanger suitable for the preconcentration of precious metal cyano complexes, the main potential problem is loss of adsorbed IIR during sample loading. This, in turn, could result in incomplete binding of the solute ions during the loading step and hence poor precision or nonquantitative recovery of the solute.

Extensive studies were undertaken to determine the ionic retentive capacities (IRCs) of concentrator columns prepared by equilibrating a C18 precolumn with different mobile phases. The percentage of acetonitrile was varied while the [IIR] in the conditioning eluent was maintained at 5 mM. Both the equilibrium IRC obtained by equilibration of the column with excess nitrate ion and the effective IRC obtained by using breakthrough techniques with a standard solution of aurocyanide were used. Table I1 compares the measured equilibrium and effective IRCs of the precolumns.

A linear decrease in effective IRC was observed for increasing percentages of acetonitrile in the conditioning eluent, with effective IRC falling to zero a t about 55% acetonitrile in the eluent. The mobile phase composition found to be optimal for detection sensitivity and resolution of the precious metal cyano complexes was 32% acetonitrile (see Table I) and a t this composition, the effective IRC of the concentrator column was measured to be 0.04 yequiv. This corresponded to 7.8 mL of a 1 ppm gold solution and was ample for the intended application of the concentrator column. The large disparity between the equilibrium and effective IRCs was consistent with previous results for chemically bonded ion- exchange precolumns (16) and styrene-divinylbenzene precolumns permanently coated with hydrophobic IIRs (17) . The results suggested that some of the bound IIR was not acces-

c PIC A PIC A

i 2 3 L 5 Volume (ml)

Flgure 2. Effect of the type of I I R on the linearity of preconcentration calibration plots; sample, 50 ppb (as Au) aurocyanide in 2 ppm cyanide, loaded at 1.0 mL/min.

sible for solute binding under dynamic conditions and showed that the equilibrium IRC was not a reliable indicator of the extent to which a solute ion can be bound to a concentrator column during sample loading.

Nature of the IIR. The effect of changing the nature of the IIR was studied by preparing calibration plots for aurocyanide by loading increasing volumes of a 50 ppb solution in 2 ppm cyanide onto columns conditioned with mobile phases containing different IIRs. Waters Associates PIC A and Low UV PIC A and tetraethylammonium chloride (TEA+Cl-) were used as IIRs. The first two IIRs are pro- prietary preparations containing tetrabutylammonium ions with different counterions.

The results are given in Figure 2 which shows that the two tetrabutylammonium IIRs gave linear calibration, and hence quantitative binding of aurocyanide, up to a sample volume of approximately 3 mL, whereas the TEAtC1- IIR showed linearity only up to 0.5 mL of sample. The departure from linearity in each case occurred at a point well below the measured effective IRC operating under the eluent conditions used; for example, the effective IRC for the Low UV PIC A reagent was 0.04 yequiv, whereas linearity was lost when 0.0008 pequiv of aurocyanide was loaded. One possible factor con- tributing to the onset of incomplete binding of aurocyanide was loss of adsorbed IIR resulting from the passage of sample through the concentrator column. It should be remembered here that a sample volume of 3 mL was equivalent to approximately 60 column volumes for the concentrator column used, and hence some loss of the adsorbed layer of IIR can be expected occur. The results can be rationalized in terms of the relative hydrophobicities of the IIRs, with the more hydrophobic tetrabutylammonium IIRs showing better ad- hesion to the column than the less hydrophobic tetraethylammonium IIR.

For all subsequent studies, the Low UV PIC A reagent was employed as the IIR because of the improved detectability at 214 nm offered by this reagent. A typical chromatogram obtained for the preconcentration of 2 mL of a 50 ppb aurocyanide standard solution is given in Figure 3. Comparison of the peak widths for aurocyanide obtained with direct injection (Figure 1) and preconcentration (Figure 3) illustrates that the solute was retained as a compact band on the concentrator column.

Reproducibility of Column Conditioning. The reproducibility of the conditioning procedure used to prepare the concentrator columns was evaluated by use of a number of new and used precolumns. The performance of these columns was assessed quantitatively by determining the effective IRC and then using each precolumn in a preconcentration run. Table I11 lists t,he effective IRCs calculated for each preco-

ANALYTICAL CHEMISTRY, VOL. 60, NO. 6, MARCH 15, 1988 539

Table IV. Effect of Sample Loading Parameters on Recovery"

sample concn, loading flow

sample vol, mL PPb rate, mL/min recovery, %

2.0 50 0.5 97.6 2.0 50 1.0 98.9 2.0 50 2.0 89.0 2.0 50 3.0 87.2 2.0 50 5.0 83.1 1.0 100 1.0 98.5 3.0 67 1.0 92.7 5.0 20 1.0 28.9

10.0 10 1.0 14.1

"In all cases the amount of aurocyanide loaded was identical (100 ng). -

O L 8 1 2 Time IminJ

Figure 3. Typical chromatogram obtained for a preconcentrated aurocyanide sample; sample, 2 mL of 50 ppb (as Au) aurocyanide In 2 ppm cyanide.

Table 111. Reproducibility Data for Chromatographic Behavior of Different Precolumns Conditioned with 32% Acetonitrile Containing 5 mM Low UV PIC A

effective capacity factor precolumna IRC, bequiv for aurocyanide recovery, %

A B C D

0.088 4.28 93.5 0.090 4.20 93.5 0.118 4.60 99.7 0.164 4.36 95.6

"See text for a description of the histories of the precolumns used.

lumn, along with the capacity factor for aurocyanide and recoveries obtained from the preconcentration determinations. Here the recovery was assessed by comparing the area of the aurocyanide peak obtained by using a preconcentration run with that from a manual injection of an equivalent amount of aurocyanide. That is, a preconcentration run using 2 mL of a 50 ppb solution was compared with a direct injection of 10 pL of 10 ppm; in both cases, the total amount of aurocyanide was 100 ng.

Precolumn A had been previously used as a concentrator column, and when compared to the new precolumns (B, C, and D), i t can be seen that the effective IRC of A was somewhat less than the average value obtained for the new columns. Differences were observed in the effective IRCs of the new precolumns, but the recoveries obtained were essentially constant. This was expected since a difference in recovery would have been evident only when the amount of solute loaded approached the effective IRC of the concentrator column.

I t was also noticed that the newly purchased precolumns did not initially provide the expected degree of binding of solute ions during the effective IRC determinations. Treat- ment with acetonitrile prior to equilibration with the eluent was found to rectify this problem, and this initial washing step has been found necessary by other workers (17, 18). The performance of the concentrator columns was essentially constant with use up to the point where voids appeared in the packing material as a result of mechanical damage caused by the pressure shocks incurred when the columns were switched into and out of the eluent stream.

Sample Loading Parameters. Two possibilities existed for variation of the amount of sample loaded onto the concentrator column, either the flow rate a t which the sample

was passed through the concentrator column could be changed or a constant flow rate could be maintained with the time for which the sample was loaded being varied. The relative merits of these approaches were evaluated by determining recoveries under different sample loading conditions. Firstly, the flow rate used for sample loading was varied, while keeping constant the total amount of sample ions concentrated at a level well below the effective IRC of the concentrator column. In this way, the recoveries were not influenced by effects relating to the IRC. The selected experimental range was 0.5-5 mL/min, with the loaded amount being equivalent to a 2-mL sample containing 50 ppb of aurocyanide.

Secondly, the effect of variation of the sample volume was studied by concentrating samples with volumes in the range 0.5-20 mL at a flow rate of 1 mL/min. Sample concentrations were adjusted so that the total amount of solute ions loaded in each case was constant (2 mL of 50 ppb aurocyanide). I t should be noted here that the samples used in this aspect of the study were made up in 100 ppm cyanide, so the larger sample volumes contained a proportionally higher total amount of ionic species.

The average results from duplicate measurements are given in Table IV from which it can be seen that the recoveries showed only a slight dependence on flow rate over the experimental range studied; however recoveries were strongly influenced by sample volume. The observed dependence of recovery on the flow rate used for sample loading differed from that found in previous studies on the preconcentration of solutes using concentrator columns with chemically bound functionalities (191, where recoveries were constant for flow rates up to 8 mL/min. I t can be expected that desorption of the IIR from the stationary phase of the concentrator column would be accelerated under conditions where flow turbulence would exist.

On the other hand, a strong dependence of recovery on the volume of sample was apparent, with quantitative recoveries being obtained only for sample volumes of 2.5 mL or less. This behavior was attributable either to desorption of bound IIR during passage of the sample or to competition for ionic sites by the increased amounts of cyanide ions present in the larger sample volumes. On consideration of the fact that the calibration plot prepared with Low UV PIC A as the IIR showed a departure from linearity a t approximately the same sample volume when only 2 ppm cyanide was present in the sample, the former of the above explanations seems the more likely.

Preconcentration of Precious Metal Complexes. With the establishment of the optimal conditions for sample preconcentration, calibration plots were prepared with 2 mL of sample loaded at 1.0 and 2.0 mL/min. The results showed that linearity was preserved a t least up to sample concentrations of 100 ppb, although the slope of the calibration plot

540 ANALYTICAL CHEMISTRY, VOL. 60, NO. 6, MARCH 15, 1988

r l i i , , , 0 2 L 6 8 1 0 1 2

Tlmelmin I

Figure 4. Ultratrace analysis of aurocyanlde in a high cyanide matrix.

0 1 i 6 i Ib1'2 Tune lmin 1

Fbgure 5. Simultaneous determination of the cyano complexes of ANI), Pd(II), and R(I1).

was slightly lower for the higher flow rates. This highlighted the importance of maintenance of constant sample loading conditions for all analyses. Figure 4 shows a chromatogram obtained for a 2-mL sample containing 10 ppb gold in a matrix containing a large excess of cyanide (100 ppm). Here, the retention time of aurocyanide was increased slightly in comparison to that shown in Figure 3 and this can be attributed

to displacement of the band of aurocyanide along the concentrator column by the high concentration of cyanide during sample loading, leading to later elution from the concentrator column in the back flush step. The detection limit was calculated to be 0.43 ppb for a 2-mL volume loaded onto the precolumn. The relative standard deviation of the aurocyanide peak area in 10 replicate sample loadings under the conditions shown in Figure 4 was 0.9%.

The possibility of resolving other precious metal cyano complexes by using the same chromatographic conditions was also investigated. Figure 5 shows a chromatogram obtained by preconcentrating 2 mL of a solution containing 10 ppb Au(1) and 5 ppb each of Pd(I1) and Pt(II), made up in 100 ppm cyanide. The three cyano complexes were clearly resolved, showing that the proposed method was suited to the simultaneous determination of these precious metals a t ultratrace levels. The additional peaks present in the chromatogram shown in Figure 5 are caused predominantly by residual sample remaining in the interstices of the concentrator column. I t is also possible that metal cyanides (e.g. Fe(II), Fe(III), and Ni(I1)) may be formed by reaction of the cyanide matrix solution with the large surface area steel end-frits used in the column.

Registry NO. Au, 7440-57-5; Pd, 7440-05-3; Pt, 7440-06-4; CK, 57-15-5; Bu~N', 10549-76-5.

LITERATURE CITED (1) Beamish, F. E.; Van Loon, J. C. Analysis of Noble Metals; Academic:

New York, 1977. (2) Brooks, R. R.; Holzbecher, T.; Ryan, D. E.: Zhang, H. F.; Chatterjee, A.

K. At. Spectrosc. 1981, 2 , 151-154. (3) Groenewald, T. Anal. Chem. 1988, 40, 863-866. (4) Wemyss, R. B.; Scott, R. H. Anal. Chem. 1978, 50, 1694-1697. (5) Alexander, R.; Kinsealla, B.; Middleton, A. J . Nectroanal. Chem.

1978, 93, 19-27. (6) Coombes, R. J.; Chow, A. Talenta 1979, 26 , 991-998. (7) Hoffman, E. E.; Naklrett, A. J.; Van Loon, J. C.; Hancock, R. G. V.;

Manson, A. Anal. Chim. Acta 1978, 702, 157-166. (8) Hllton, D. F.; Haddad, P. R. J. Chromatogr. 1986, 357, 141-150. (9) Seymour, M. D.; Fritz, J. S. Anal. Chem. 1973, 45, 1394-1399.

(10) Rocklln, R. D. Anal. Chem. 1984, 56, 1959-1962. (11) Haddad, P. R.: Heckenberg, A. L. J . Chromatogr. 1985, 378,

279-288. (12) Heckenberg, A. L.; Haddad, P. R. J. Chromatogr. 1985, 330, 95-111. (13) Jackson, P. E.; Haddad, P. R. J. Chromatogr. 1986, 355, 87-97. (14) BMlingmeyer, B. A. J. Chromatogr. Sci. 1980, 78, 525-539. (15) Haddad, P. R.: Heckenberg, A. L. J. Chromatogr. 1984, 300,

357-394. (16) Jackson, P. E.; Haddad, P. R. J. Chrornatcgr. 1987, 389, 65. (17) Haddad, P. R.; Jackson, P. E. J. Chrornatcgr. 1987, 407, 121. (18) Dreux, M.; Lafosse, M.; Agba-Hazoume, P.; Chaabane-Doumandji, B.;

Gilbert, M.; Levl, Y. J . Chromatogr. 1986, 354, 119. (19) Haddad, P. R.; Jackson, P. E. J. Chromatogr. 1988, 267, 301-309.

RECEIVED for review June 29,1987. Accepted November 27, 1987. Presented in part a t the 9th Australian Symposium on Analytical Chemistry, Sydney, Australia, April 1987.

determination of trace levels of gold(i) as its cyano complex by ion-interaction reversed-phase...

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