Efficient Photochemical Vapor Generation of Molybdenum for ICPMS Detection

Photochemical vapor generation (PVG) of Mo was accomplished using a 19 W high-efficiency flow-through photoreactor operating in a flow injection mode using 30-50% (w/v) formic acid as a reaction medium. The generated volatile product (most probably molybdenum hexacarbonyl) was directed by an argon carrier gas to a plastic gas-liquid separator and introduced into the spray chamber of an inductively coupled plasma mass spectrometer for detection. Particular attention was paid to the determination of overall PVG efficiency relative to that for liquid nebulization. Utilizing a sample flow rate of 1.25 mL min^-1, corresponding to an irradiation time of 38 s, PVG efficiencies in the range 46-66% were achieved. The efficiency could be further enhanced by the presence of mg L^-1 added Fe³⁺ ions. A limit of detection of 1.2 ng L^-1 and precision of 3% (RSD) at 250 ng L^-1 were achieved. Interferences from inorganic anions likely to be encountered during analytical application to real samples (NO₃^-, Cl^-, SO₄^2-, NO₂^-, and ClO₄^-) were investigated in detail. The accuracy and applicability of this sensitive methodology was successfully verified by analysis of fresh water Standard Reference Material NIST 1643e, two seawater Certified Reference Materials (NASS-7 and CASS-6), and by analysis of two samples of commercial dietary supplements solubilized in formic acid.