DIRECT LIQUID ABLATION - A NEW CALIBRATION STRATEGY FOR LASER-ABLATION ICP-MS MICROANALYSIS OF SOLIDS AND LIQUIDS

Trace elements in microliter quantities of aqueous solutions were anal ysed by direct liquid ablation using an 193 nm excimer with an inducti vely coupled plasma mass spectrometer (ICP-MS). Fractionation resultin g from splashing and evaporation can be minimised by covering the liqu id surface with a thin plastic film, through which a 20 mu m hole is d rilled with the laser. Particle-size distribution and oxide formation in the plasma resulting from the direct liquid ablation are similar to those generated by solid ablation. The ICP-MS response in cps/ppm is approximately 100 x higher for the direct ablation, but is proportiona l to the response from solid ablation, within an accuracy < 15% for mo st trace elements in NIST 610 and NIST 612 glass standards. A matrix l oad up to 2.5 wt.-% NaCl in the solution does not affect the proportio nality of trace element responses. Thus, direct liquid ablation is not only suited for analysing small volumes of complex aqueous solutions (e.g., the quantitative microanalysis of fluid inclusions in minerals) , but also provides a new approach for calibrating laser ablation ICP- MS microanalysis of solids.