A calibration strategy for LA-ICP-MS analysis employing aqueous standards having modified absorption coefficients

Laser ablation ICP-MS is a powerful technique for the direct elemental analysis of solids with spatial resolution down to a few microns. However, its range of application is limited by the lack of calibration standards. This paper describes a novel approach to calibration that employs aqueous standards whose absorption coefficients are modified, by the addition of a chromophore, to produce the desired ablation yield. Chromophores for the important laser wavelengths at 193, 248 and 266 nm are given. The mechanism of ablation and parametric dependences for the modified aqueous standards were investigated and it was concluded that ablation proceeds by a three step process leading ultimately to nebulisation of the bulk liquid. This is important as such a process should not involve fractionation between elements. Calibration curves produced using the aqueous standards were linear and reproducible, but internal standardisation is required to provide linked calibration for real samples. NIST standard Reference Material 613 Trace Elements in Glass and low density polyethylene were analysed and the results agreed with reference values or those obtained by other techniques.