Method development for simultaneous multi-element determination of transition (Au, Ag) and noble (Pd, Pt, Rh) metal volatile species by microwave induced plasma spectrometry using a triple-mode microflow ultrasonic nebulizer and in situ chemical vapor generation

Abstract

The analytical potential of a coupled continuous-microflow ultrasonic nebulizer triple-mode micro capillary system (μ-USN/TCS)-Ar/He mixed gas microwave induced plasma-optical emission spectrometry (MIP-OES) has been evaluated for the purpose of determination of metal volatile species (Au, Ag, Pd, Pt, Rh). An extremely short reaction time between sample, acid and reductant and a rapid separation of the reaction products is obtained by mixing the sample, acid and the sodium borohydride reductant solution at the quartz oscillator, converting liquids into aerosol at the entrance to the spray chamber. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Results showed that the analytical performance of the new system was superior to that of ultrasonic nebulizer dual-mode capillary system. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the μ-USN/TCS observed at a 15 μL min−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of the standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1.2, 1.5, 1.1, 2.9 and 1.8 ng mL−1 for Au, Ag, Pd, Pt and Rh, respectively. The method offers relatively good precision (RSD ranged from 7 to 8%) for liquid analysis and microsampling capability. The accuracy of the method was verified using certified reference materials (TORT-1, NIST 2710, NIST 1643e, IAEA-336) and by the aqueous standard calibration technique. The measured contents of elements in reference materials were in satisfactory agreement with the certified value (Ag) and added amounts (Au, Pd, Pt, Rh).