Evaluation of laser-induced and ICP-induced elemental fractionation using laser ablation-ICP-TOFMS†

The composition of laser-generated aerosols produced during single spot ablation was analyzed via inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOFMS) and compared with that of the same material deposited on the sample surface. Differences between the signals recorded from single spot ablation and the subsequent deposit analysis enabled studying and exploring non-stoichiometric processes at the ablation site. These measurements allowed for the determination of the transport efficiencies of the elements present in NIST SRM 610, which were element-specific and always higher than 85%. A mass balance of ²³⁸U⁺/²³²Th⁺ signal intensity ratios allowed the differentiation of laser-induced and ICP-induced elemental fractionation using only LA-ICP-TOFMS data, without the need for the off-line analysis of the collected material. All phenomena reported herein were studied using a range of parameters for single spot ablation including different laser fluences (7.4–25 J cm⁻²) and number of pulses per spot (100–600 pulses). The method presented here provides direct access to important parameters that influence the accuracy of quantitative analysis using LA-ICPMS, such as the amount and composition of the deposited material around the crater and information about the aforementioned transport efficiencies of individual elements. In addition, the proposed analysis and calculation procedure allowed to distinguish between laser- and ICP-induced elemental fractionations for different LA and ICPMS operating conditions. Knowledge about these parameters will help understand the ablation behavior of different matrices and may therefore improve non-matrix matched quantification using LA-ICPMS.