CHEMICAL FRACTIONATION DURING INFRARED AND ULTRAVIOLET-LASER ABLATIONINDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY - IMPLICATIONS FOR MINERAL MICROANALYSIS

The silicate glass standard reference material NIST SRM 610 has been r epeatedly analysed by UV and IR laser ablation ICP-MS in procedures de signed to mimic typical analytical procedures adopted during mineral a nalysis, Trace element fractionation during both IR and UV laser ablat ion is observed and relationships between fractionation trends and ion ic radius, charge and melting temperature of the elements determined a re defined and discussed, In particular the high field strength elemen ts (e.g., Nb, Ta, Zr, Hf) all show decreasing fractionation trends wit h respect to Si in the NIST SRM 610 glass during repeated laser ablati on, whilst the low field strength and large ion lithophile elements (e ,g., Rb, Sr, Pb, Ba, Ca) all show increasing trends with respect to Si , For IR laser ablation the degree of fractionation observed in the an alysis of the REEs is strongly correlated to their ionic radii, In all the analytical procedures studied, fractionation arising from IR lase r ablation is considerably greater than UV laser ablation and simple c hanges to analytical procedure to reduce trace element fractionation a re suggested, For UV laser ablation, the effect of laser focus on anal ytical precision is assessed, Active focussing of the laser during abl ation under computer control significantly improves analytical precisi on.