Method Development for Simultaneous Determination of Transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and Noble (Pd, Pt, Rh) Metal Volatile Species by Microwave-Induced Plasma Spectrometry Using Ultrasonic Micronebulizer Dual Capillary Sample Introduction System

ABSTRACT

The commercial ultrasonic nebulizer NOVA-DUO (Optolab, Warsaw, Poland) has been evaluated for the simultaneous determination of transition (Au, Ag, Cd, Cu, Mn, Ni, Pb, Zn) and noble (Pd, Pt, Rh) volatile metal species by microwave induced plasma–optical emission spectrometry (MIP-OES). Simultaneous mixing and nebulization of the two solutions (acidified sample and reductant) on the piezoelectric transducer, with the possibility of flow rate adjustment, permits a wide variation of sensitivity. The vapor-phase species were rapidly transported via a stream of Ar carrier to an MIP–OES for simultaneous multi-element determination. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the ultrasonic nebulizer/dual capillary system (USN/DCS) observed at 15 µL min⁻¹ flow rate. An improvement in detection limits was achieved compared with pneumatic nebulization. Detection limits are superior to conventional pneumatic nebulization of elements. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of standard deviation of the blank (LOD, 3σ_blank criterion, peak height), were 2.49, 1.75, 3.39, 2.13, 4.80, 6.21, 4.26, 2.01, 7.65, 3.92, and 4.65 ng mL⁻¹ for Au, Ag, Cd, Cu, Mn, Ni, Pb, Pd, Pt, Rh, and Zn, respectively. The method offers relatively good precision (RSD ranged from 8 to 12%) for liquid analysis and microsampling capability. The accuracy of the method was verified by the use of digested certified reference materials (NRCC TORT-1, NIES CRM-13, NIST SRM 2710, INCT SBF-4) and by aqueous standard calibration technique. The measured elements content in reference materials was in satisfactory agreement with the certified values.

KEYWORDS:

• chemical vapor generation
• dual-mode sample introduction system
• microwave-induced plasma–optical emission spectrometry
• transition and noble metals
• ultrasonic nebulizer

ACKNOWLEDGMENT

Financial support by the Committee for Scientific Research, Poland (Grant No. COST/48/2006), is gratefully acknowledged.

Notes

^a Detection limit defined by three blank criterion (n = 6).

^b For sample weights of 300 mg.

^c Sample solution flow rate of 15 µL min⁻¹.

^d Enhancement (improvement factor).

^a Results are expressed in µg g⁻¹.

^b Mean ±standard deviation (n = 3).

^c Added amount.

^d Below detection limit.

^e Information (uncertified) value.