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ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978
Simultaneous Determination of Platinum Group Metals and Gold, in Ores and Related Plant Materials by Inductively Coupled Plasma-Optical Emission Spectrometry R. B. Wemyss JCI Minerals Processing Research Laboratory, P.O. Box 130 17, Knights 74 13, Republic of South Africa
R. H. Scott" National Physical Research Laboratory, CSIR, P.O. Box 395, Pretoria 000 7, Republic of South Africa
A method has been investigated for the simultaneous determination of trace quantities of the platinum group metals in aqueous solutions derived from ores and related plant materlals. The method is applicable to both high and low grade rnaterlals, and it is necessary in the case of the low grade materials to do a preliminary collection of the platinum group metals in a nickel sulfide button. Preliminary work was undertaken using an inductively coupled plasma (ICP) source and a monochromator, and the final analysis was carried out on a commercial ICP/spectrometer system with computer. Results obtained on some standard materials were compared with recommended values and values obtained by atomic absorption spectrometry. The ICP method was found to yield satisfactory results, and is recommended as an alternative analytical method for the rapid determination of platinum group metals in the above materials.
Trace quantities of t h e platinum group metals can be determined colorimetrically ( I ) , but spectroscopic methods (2) generally provide a more rapid and convenient means of determining these elements. T h e development of the inductively coupled plasma source has revived interest in the emission spectrometric analysis of
solutions. In view of the multielement capability of emission spectrometry, and the favorable reports on the ICP source with regard to detection limits, reproducibility, and relative freedom from matrix effects ( 3 ) , it was decided to investigate the determination of the platinum group metals using ICP-OES (inductively coupled plasma-optical emission spectrometry). On hand was an ICP source with monochromator which was used for studying various spectral emission lines and a commercial ICP/spectrometer system with computer, which provided for rapid multielement analysis. To evaluate the ICP method, a number of "in house" standards were analyzed. Results were compared with recommended values and also with values obtained by atomic absorption spectrometry. S t a n d a r d s a n d Sample Preparation. Stock Solutions. Solutions containing 1000 pg/mL of the following metals were prepared: Pt, Pd, Rh, Ir, Ru, Os, Au, Cu, Xi, and Fe. The preparative procedure for the platinum group metals and gold is given in reference 4. The base metal solutions were prepared from Johnson Matthey Specpure metals by acid dissolution. The above solutions were diluted and combined as required. All solutions aspirated contained 10% v / v "OB. Ores and Related Plant Materials. Sample masses and dilution factors were chosen so that the anticipated concentrations of platinum metals in the final solutions were in the calibration ranges given in Table 111. The samples were dissolved as follows (duplicate solutions were prepared for each sample).
Table I. Instrumentation System 1 R F generator spectrometer
readout
computer plasma torch assembly nebulizer and spray chamber
System 2
frequency 27 MHz, stabilized R F forward power frequency 27 MHz, power fixed at 1.25 kW (Applied Research Laboratories adjustable from 0-4 kW, ll/, turns load coil (International Plasma Corp. Model PM 1 4 0 - 2 7 ) 33000 LA) 0.5-m Jarrell-Ash monochromator, grating ruled ARL 3 3 000: 1-m Sequentometer, grating ruled 1920 lines mm-l, 0.5 nm mm-' 1180 lines m m - ' , 1.6 nm mm-' reciprocal reciprocal linear dispersion (1st order), linear dispersion (1st order), slit width 20 pm primary slit width 20 Mm, secondary X 5 m m slit height, Hamamatsu type R106 slits normally 50 o r 7 5 Mm, EM1 9750 photomultiplier phototubes Linear picoammeter with bu,ilt-in preamplifier, digital readout of integrated signal zero suppression and variable damping (Keithley Instruments, Model 4 1 7 ) . Stripchart recorder with 0.65-s fsd time constant (Hitachi, Model QD 15) dedicated mini-computer with 8 K not applicable memory (Digital Equipment Corp PDP 1105) fused quartz with capillary injector, fused quartz with capillary injector ( 7 ) (design by ARL but similar to ( 7 ) ) glass pneumatic concentric nebulizer glass pneumatic concentric nebulizer (8) (design by J. E. Meinhard) into dual (design by CSIR) and Tefloniglass crossflow tube spray chamber similar to (8). nebulizer (IO). Both used with dual tube Solution pumped at a constant rate to spray chamber ( 9 ) . nebulizer by peristaltic pump
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0003-2700/78/0350-1694$01 0010
C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 12, OCTOBER 1978
EXPERIMENTAL
Table 11. Operating Conditions for Plasma System 1 forward R F power reflected power argon coolant/support gas flow rate argon flow rate for aerosol transport height of observation above load coil sample solution uptake rate integration time ~~
System 2 (ARL) Instrumentation. The two ICP systems are described in Table
1.0 kW
