Time-of-flight mass spectrometric detection of mono- and di-substituted benzenes at parts per million concentrations by way of liquid microjet injection and laser ionisation
Wl. Holstein et al., Time-of-flight mass spectrometric detection of mono- and di-substituted benzenes at parts per million concentrations by way of liquid microjet injection and laser ionisation, INT J MASS, 207(1-2), 2001, pp. 1-12
266 nm 1+1 resonance-enhanced multiphoton ionisation has been used in conju
nction with a liquid microjet time-of-flight mass (TOF) spectrometer to det
ect anisole, 4-methoxyphenol and hydroquinone in ethanol solution. We have
demonstrated a detection limit of 1 ppm for the parent molecular ion of hyd
roquinone. A comparison of TOF mass spectra of samples introduced by way of
the liquid beam with those entrained in a supersonic free-jet expansion sh
ows that the solute molecules are ionised after evaporation from the surfac
e of the liquid beam. Extensive fragmentation of each parent molecular ion
is attributed to excess energy available to the molecules by way of additio
nal photon absorption following the initial photoionisation event. Hydroqui
none photoion fragmentation patterns are found to be independent of laser p
ower in the range 2.4-7.1 GW/cm(2), suggesting that saturation of the multi
photon fragmentation channels has been achieved. (C) 2001 Elsevier Science
B.V.