A comparison of 266 nm, 213 nm and 193 nm produced from a single solid state Nd:YAG laser for laser ablation ICP-MS

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Abstract
Laser ablation using wavelengths of 266 nm, 213 nm and 193 nm as a sampling method for ICP-MS was compared. Unlike previous studies, this was performed under essentially identical laser ablation conditions with the exception of wavelength. This was achieved by using a single solid state laser source (1064 nm Nd:YAG) for harmonic generation together with sum frequency mixing and optical parametric oscillation. Experiments were carried out on the NIST 600 series silicate glasses. Particle size distributions for all three wavelength were measured and increased in the order 193 nm < 213 nm < 266 nm. This effect is related to the absorption behaviour of the sample opaque < transparent at each wavelength. The change towards larger particle sizes with increasing wavelength is influencing the noise in the transient signals and their intensity ratios. A smaller number of particles with diameters of >150 nm are produced in comparison to longer wavelengths when ablating with 193 nm. Due to the decreased amount of particles above 0.15 µm vaporisation induced elemental fractionation within the ICP, especially for more transparent samples is reduced. Data on the behaviour of 213 nm ablation and resulting ICP-MS response demonstrated that this wavelength is intermediate between 193 nm and 266 nm, but biased towards 193 nm for more opaque samples and biased towards 266 nm for those more transparent. This study (maintaining laser parameter constant and not exceeding depth to diameter ratios of 2∶1) shows that the wavelengths in first instance are responsible for particle size distribution and that their distribution leads to enhanced vaporisation, atomisation and ionisation effects within the ICP. Until now, only 193 nm produced particle sizes (as shown for the selection of silicate samples) can be stoichiometrically converted into ions using common ICP-MS instruments.