Inter-element fractionation and correction in laser ablation inductively coupled plasma mass spectrometry

Inter-element fractionation in laser ablation inductively coupled plasma ma ss spectrometry (LA-ICP-MS) analysis is one of the major challenges for usi ng the technique for in situ trace element determination and isotopic ratio measurement of geological, environmental and biological solid samples. Att empts have been made to reduce inter-element fractionation in LA-ICP-MS ana lysis. However, this fractionation cannot be eliminated. The mechanism of t he fractionation in LA-ICP-MS analysis is not very well understood. This st udy investigated the inter-element fractionation of seven elements (Ca, V, Zn, Ga, Sr, La and Nd) in three different sample matrices (NIST 613, BCR-2 and SY-4) using a UV 266 nm laser. The study showed that the inter-element fractionation depends on the sample matrices and varies with time. The inte r-element fractionation behaviour of V, Zn and Ga in the synthetic silicate glass NIST 613 is different from that in the quenched glass of fused silic ate rocks (BCR-2 and SY-4). Relative to Ca, V, Zn and Ga show less fraction ation in NIST 613 but larger fractionation in BCR-2 and SY-4. The relative internal standard normalized element intensity (RISNEI) is not linear with time for a laser ablation period of 210 s. Therefore, data acquisition usin g prolonged laser ablation without a matrix match will not improve the prec ision and accuracy for elements whose fractionation behavior is different f rom that of the internal standard element. The RISNEI versus time relations hip for the first 100 s laser ablation can be treated as linear to simplify the data calculation. In this paper, the internal standard normalized frac tionation factor (ISNFF) is defined as the sum of the second half average R ISNEI and the difference between the second and first half average RISNEI, divided by the second half RISNEI of data acquisition, for the analyte conc entration calculation. The ISNFF was applied for the correction of the data reduction in LA-ICP-MS analysis. The data accuracy for these seven element s is generally improved, particularly for an element whose calibration stan dard normalized ISNFF is significantly greater or less than 1 (e.g., Zn and Ga in this study). Good accuracy can be obtained for elements without ISNF F correction and matrix matches only if the calibration standard normalized ISNFF of the elements is close to 1.