Inductively coupled plasma optical emission spectrometry (ICP-OES) determination of platinum was optimized using 2-level, 4-factor full factorial design and response surface methodologies. Four factors, namely carrier gas flow rate, sample solution flow rate as represented by the pump speed, plasma observation height and RF power, were employed in the factorial design. Analysis of variance (ANOVA) at a p-value significance level of 0.05 was used to assess the significance of the factors on platinum analytical line emission intensity. The main effects of carrier gas flow rate and plasma power, and the interaction effect of carrier gas flow rate and plasma power, were found to be statistically significant and were varied during subsequent optimization procedure using contour map and response surface methodologies. Plasma observation height and pump speed were found to have an insignificant effect on the platinum intensity and were held constant at 10 mm above the load coil and 30 revolutions per minute, respectively during the optimization procedure. The optimized procedure comprised of a carrier gas flow rate of 0.70 L/min and plasma power of 1400 W, and was validated by analysis of Certified Reference Materials (CRMs) AMIS 0132 for low platinum grades and AMIS 0164 for high platinum grades. The instrumental limit of detection (LOD) and limit of quantization (LOQ) obtained were 0.035 µg/g Pt and 0.105 µg/g Pt, respectively, and highly precise determinations of Pt (0.21 to 0.24% RSD) were obtained when three batches of PMG ore floatation concentrates were analyzed using the optimized ICP-OES parameters.
Key words: Factorial experimental design, response surface methodology, optimization, inductively coupled plasma atomic optical spectroscopy, platinum.