LASER-DESORPTION FAST GAS-CHROMATOGRAPHY - MASS-SPECTROMETRY IN SUPERSONIC MOLECULAR-BEAMS

A novel method for fast analysis is presented. It is based on laser de sorption injection followed by fast gas chromatography-mass spectromet ry (GC-MS) in supersonic molecular beams. The sample was placed in an open air or purged laser desorption compartment, held at atmospheric p ressure and near room temperature conditions. Desorption was performed with a XeCl Excimer pulsed laser with pulse energy of typically 3 mJ on the surface. About 20 pulses at 50 Hz were applied for sample injec tion, resulting in about 0.4 s injection time and one or a few microgr ams sample vapor or small particles. The laser desorbed sample was fur ther thermally vaporized at a heated kit glass filter located at the f ast GC inlet. Ultrafast GC separation and quantification was achieved with a 50-cm-long megabore column operated with a high carrier gas flo w rate of up to 240 mL/min. The high carrier gas flow rate provided ef fective and efficient entrainment of the laser desorbed species in the sweeping gas. Following the fast GC separation, the sample was analyz ed by mass spectrometry in supersonic molecular beams. Both electron i onization and hyperthermal surface ionization were employed for enhanc ed selectivity and sensitivity. Typical laser desorption analysis time Tvas under 10 s. The laser desorption fast GC-MS was studied and demo nstrated with the following sample/matrices combinations, all without sample preparation or extraction: (a) traces of dioctylphthalate plast icizer oil on stainless steel surface and the efficiency of its cleani ng; (b) the detection of methylparathion and aldicarb pesticides on or ange leaves; (c) water surface analysis for the presence of methylpara thion pesticide; (d) caffeine analysis in regular and decaffeinated co ffee powder; (e) paracetamol and codeine drug analysis in pain relievi ng drug tablets; (f) caffeine trace analysis in raw urine; (g) blood a nalysis for the presence of 1 ppm lidocaine drug. The features and adv antages of the laser desorption fast GC-MS are demonstrated and discus sed. (C) 1998 American Society for Mass Spectrometry.