Ultra-micro analysis of liquids and suspensions based on laser-induced plasma emissions

Spectrochemical analysis of liquids and suspensions using laser-induced plasma emissions was investigated. Nd:YAG pulsed-laser 532-nm.ablation of aqueous samples produced plasmas that were hot few eV.and extensively ionized, with electron density in the 1018 cmy3 range. Analyte line signals were initially masked by intense plasma continuum emissions, and would only emerge briefly above the background when the plume temperature dropped below 1 eV during the course of its very rapid cooling. In contrast, 193-nm laser ablation at similar fluence generated plasmas of much lower -1 eV. temperature but comparable electron density. The plasma continuum emissions were relatively weak and the signal-to-background ratio was a thousand times better. This ‘cold’ plasma was ideal for sampling trace amounts of biologically important elements such as sodium and potassium. By ablating hydrodynamically focused jets in a sheath-flow, and with acoustic normalization for improved precision, the single-shot detection limits of sodium and potassium were 8 and 50 fg, respectively. Using the sheath-flow arrangement, the amounts of sodium and potassium inside single human red blood cells were simultaneously determined for the first time. The intracellular contents for a given blood donor were found to vary significantly, with only very weak correlation between the amounts of sodium and potassium in individual cells. q1998 Elsevier Science B.V.