Cadmium Assisted Photochemical Vapor Generation of Tungsten for Detection by Inductively Coupled Plasma Mass Spectrometry

Efficient photochemical vapor generation (PVG) of tungsten has been achieved for the first time using a 19 W thin film flow-through photoreactor. The volatile product (most probably tungsten hexacarbonyl) was generated using a flow injection mode and 40% (v/v) formic acid as the reaction medium. An inductively coupled plasma mass spectrometer was utilized for ultrasensitive detection. The addition of Cd2+ as a sensitizer was critical, enhancing the overall PVG efficiency some 30 000-fold. At an optimal irradiation time of 19 s, a 6.1-fold enhancement factor and an overall PVG efficiency of 43% were determined from a comparison of the response to direct solution nebulization when using a sample flow rate of 2 mL min(-1) and 500 mg L-1 Cd2+ as a sensitizer. A limit of detection of 0.9 ng L-1 and repeatability (RSD) of 2% at 100 ng L-1 were achieved. Interference from inorganic acids (HNO3, HCl, H2SO4, and HF) was investigated with respect to analytical application to real samples. The accuracy and practical feasibility of this ultrasensitive methodology was successfully verified by analysis of Certified Reference Material CTA-FFA-1 (Fine Fly Ash) and six natural water samples with low W concentrations.