Factorial design for multivariate optimization of an on-line preconcentration system for platinum determination by ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry

A system for on-line preconcentration and determination of platinum by ultrasonic nebulization (USN) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) was studied. It is based on the chemical sorption of platinum on a column packed with polyurethane foam loaded with thiocyanate reagent. The optimization step was carried out using two level full factorial design. Three variables (pH, loading flow rate (LFR) and eluent concentration) were regarded as factors in the optimization. Results of the two level factorial design 23 with three replicates of the central point for platinum preconcentration, based on the variance analysis (ANOVA), demonstrated that the factors and their interactions are not statistically significant. The proposed procedure allowed the determination of platinum with a detection limit of 0.28 μg l−1. The precision for 10 replicate determinations at 10.0 μg l−1 Pt level was 3.8% relative standard deviation (R.S.D.), calculated from the peak heights obtained. A total enhancement factor of 100 was obtained with respect to ICP-OES using pneumatic nebulization (10 for USN and 10 for preconcentration). A sampling frequency of 50 samples per hour was obtained. The effect of other ions in concentrations agreeing with water samples was studied. The addition/recovery experiments in the samples analyzed demonstrated the accuracy and applicability of the system developed for platinum determination in spiked water samples.