High efficiency aerosol dispersion cell for laser ablation-ICP-MS

Abstract

A novel ablation cell for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed. The “high efficiency aerosol dispersion” (HEAD) ablation cell is based on the use of a directed gas flow expansion of the laser generated aerosol at the ablation site and a venturi effect created by two nozzles to extract the aerosol into the main make up gas stream, which finally transports the particles into the ICP. The figures of merit were evaluated based on the ablation of glass SRM NIST 610 using two different cell gases (Ar and He). The investigation of the capabilities of this type of aerosol extraction (using a Nd:YAG laser, λ = 266 nm) demonstrates that a laser generated aerosol can be modified (HEAD effect) by shifting the original particle size distribution towards smaller particle sizes. This effect was obtained for both gases (Ar and He) for increasing cell gas flows and showed an optimum at a flow rate of 100 ml min⁻¹. In comparison with standard cell results, elemental ratios (e.g. U/Th) showed reduced elemental fractionation effects attributed to reduced agglomeration and, therefore, an improved vaporization of the aerosol within the ICP. Most importantly, stability and reproducibility of the ion-signals were significantly improved without compromising sensitivity. In addition to the glass analysis, the HEAD ablation cell was also used for the ablation of brass samples, as this matrix is known to show pronounced elemental fractionation effects due to the thermal volatility difference of Cu and Zn. The temporal stability of element ratios (e.g. Cu/Zn) achievable using such an extraction approach (5%) was significantly improved in comparison with previously reported Cu/Zn ratios (30%) measured using standard cell configurations.