PULSED SAMPLE INTRODUCTION INTERFACE FOR COMBINING FLOW-INJECTION ANALYSIS WITH MULTIPHOTON IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY

A pulsed sample introduction (PSI) interface is developed to combine f low injection analysis with a time-of-flight mass spectrometer. In PSI , sample molecules carried by a liquid carrier such as methanol at a f low rate of 0.5 mL/min are vaporized by passing through a heated capil lary tube and then through a sample vaporizer of a high-temperature pu lsed nozzle. The resulting sample vapors are introduced into the mass spectrometer in a pulsed form and ionized by laser-induced multiphoton ionization. The applicability of this interface for the detection of volatile and nonvolatile compounds is studied. It is found that a vari ety of chemicals including molecules with environmental or biological significance can be studied by this method. Preliminary studies of the performance of this interface are reported. It is shown that reproduc ible results from repeated injection of the same concentration of samp les can be readily obtained. The average relative standard deviation i s in the range 4-8%. No memory effects and severe peak tailing are fou nd with this PSI interface. The detection limits of the present techni que are compound dependent. For aniline, tryptamine, and indole-3-acet ic acid, the detection limits are found to be 3, 4, and 140 ng, respec tively. Excellent linearity over 2 orders of magnitude of analytical r ange can be obtained for quantitation. It is also shown that cluster f ormation during the supersonic expansion is not a major problem in thi s technique.