Herein,
we report a discovery that photochemical vapor generation
(PCVG) of molybdenum (Mo) can be synergistically enhanced dramatically
by cobalt and copper ions sourced from acetates in the medium of formic
acid, utilizing a flow-through reactor. The nature of this new PCVG
was probed for the first time by an electron paramagnetic resonance
(EPR) spin trapping technique for its possible reaction mechanism.
Carboxyl and hydroxyl free radicals were verified during PCVG processes,
and the results indicate that variations in the relative amounts and
proportions of free radical species may account for the synergistic
effect from concomitant Co2+ and Cu2+, as well
as the generation of molybdenum hexacarbonyl from the UV-induced photolysis
of formic acid. Under “dry” plasma conditions, the simultaneous
spiking of Co2+ and Cu2+ to 20% (v/v) formic
acid solutions and a 60 s irradiation time could give rise to a 15-fold
enhancement in signal intensities, together with a blank-limited but
still impressive limit of detection of 6 ng L–1 (6
ppt) by inductively coupled plasma mass spectrometry (ICP-MS). The
accuracy and reliability of this methodology was validated by analysis
of molybdenum in a seawater certified reference material, CASS-6,
as well as two varieties of drinking water and seawater samples, with
satisfactory spike recoveries (91–101%).