Predicting instrumental mass fractionation (IMF) of stable isotope SIMS analyses by response surface methodology (RSM)

Instrumental mass fractionation (IMF) of isotopic SIMS analyses (CAMECA 1280HR, CRPG Nancy) was predicted by response surface methodology (RSM) for the 18O/16O determination of plagioclase, K-feldspar, and quartz. The three predictive response surface models combined instrumental and compositional inputs. The instrumental parameters were: (i) X and Y stage positions, (ii) the values of LT1DefX and LT1DefY electrostatic deflectors, (iii) chamber pressure, and (iv) primary-ion beam intensity. The compositional inputs included: (i) anorthite content (An%) for the plagioclase model, and (ii) orthoclase (Or%) and barium (BaO%) contents for the K-feldspar model. The three models exhibited high predictive power. The coefficients R2 and prediction-R2 were, respectively, 90.47% and 86.74% for plagioclase, 87.56% and 83.17% for K-feldspar, and 94.29% and 91.59% for quartz. The results show that RSM can be confidently applied to IMF prediction in stable isotope SIMS analyses by the use of instrumental and compositional variables.