AE Pillay, S Stephen, A Abd-Elhameed and JR Williams
Keywords: ICP-MS, depth-profiling, gels/waxes/pastes, laser ablation, liquid nitrogen pre-treatment.
Abstract: A rapid procedure involving liquid nitrogen pre-treatment of gelatinous samples prior to laser ablation was developed. Laser depth-profiling is usually limited to solid samples. Our technique with liquid nitrogen pre-treatment provides the unique capability to study elemental profiles in gels, waxes and “soft” samples. A range of samples including globules of hair gels, face creams, toothpaste and soap were petrified in aliquots of liquid nitrogen and immediately subjected to laser irradiation. The study was largely qualitative to demonstrate the potential of the pre-treatment approach. This format lends itself to direct multi-elemental analysis and obviates the tedium of digesting samples in mild acidic media. Depth-profiling was limited to specific depths, and rapid spatial and sub-surface distributions of metal components in the petrified samples were achieved well before “thawing” set in. An Nd:YAG deep UV (213-nm) laser ablation system was attached to a high-precision ICP-MS instrument. Irradiations were conducted with a flat-beam profile of 60% total energy and 55 ?m diameter. The laser dwell time was 5 s and the repetition rate was 10 Hz. Following iterative surface scanning on a 9-point sample grid, the laser ablated a total depth of 25 ?m at 5 ?m-intervals at each point. The experimental results showed promise and the distinct capability to record spectra in the absence of “splashing” effects. This pre-treatment approach is, therefore, highly viable, and a useful contribution to analytical science and instrumental analysis.
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