Influence of particle size on fractionation with nanosecond and femtosecond laser ablation in brass by online differential mobility analysis and inductively coupled plasma mass spectrometry

A differential mobility analyzer (DMA) passes laser ablation (LA) particles and agglomerates within a narrow range of electrical mobilities to the inductively coupled plasma mass spectrometer (ICP-MS). No particle collection or offline particle analysis is required. Fractionation is assessed with the Cu+/Zn+ signal ratio. Results presented in this paper support previous findings that ns LA provides many small Zn-rich particles and some much larger Cu-rich particles and that fs LA produces large agglomerates of small particles. The composition of the aerosol produced by fs LA falls between the relatively Zn-rich and Cu-rich extremes of ns LA. Femtosecond LA provides elemental ratio measurements that remain more stable with respect to time, which allows a greater degree of confidence in LA results. Even though some parameters besides pulse length differ between the lasers compared in this study, the suppression of particle size related fractionation with fs LA can be attributed to pulse length.