On-line concentration by analyte adsorption and subsequent laser desorption in supersonic jet spectrometry.

A narrow capillary, the tip of which was restricted to form a supersonic jet, was employed for sample introduction in time-of-flight mass spectrometry. The analyte was adsorbed at the tip of the capillary, due to a temperature decrease by the Joule-Thomson effect. Then, the analyte was desorbed using a pulsed laser emitting at 532 nm, and was entrained into a carrier gas. The analyte in the jet was subsequently ionized using a pulsed laser emitting at 266 nm. The duration of the analyte passing through the ionization region was 5.4 mm in length (9 micros in time), and the signal intensity was enhanced 310-fold. This technique can also improve selectivity by controlling the nozzle temperature, since volatile compounds are not trapped at the tip of the capillary and then are not concentrated in the jet. In this approach, the analyte can be injected in a pulsed mode into a vacuum without using a complicated mechanical valve even at a repetition rate of >1 kHz from the nozzle heated at a temperature of >300 degrees C.