Perchlorate (ClO4-) is found in both Earth and Martian surface environments, yet its formation mechanism remains enigmatic. ClO4- isotope composition can help to identify the formation mechanism/source, but the conventional gas-source isotope ratio mass spectrometry (IRMS) method requires micromole or larger sample sizes together with tedious mineral precipitation steps. Here, a capable method for measuring δ37Cl, δ18O, and Δ17O values of trace ClO4- (6) can improve Δ17O precision, but inducing scale distortion caused by space-charge effects for the δ18O and Δ17O. Our method could reach the accuracy of 0.6‰ for Δ17O (AGC Target ≈ 2 × 106) and 0.6‰ and 0.7‰ for δ37Cl and δ18O (AGC Target ≈ 1 × 106), respectively, in 8.40 nmol sample. Across a sample size range of 0.84 to 8.40 nmol of ClO4-, the uncertainties remained ≤1.4‰ under both optimal and nonoptimal electrospray conditions. Man-made ClO4- from commercial sources and natural ClO4- from the Atacama Desert exhibited IRMS differences within 1‰ after purification and concentration control by ion chromatography. The method enables perchlorate isotope application to atmospheric, environmental, and planetary samples previously inaccessible due to sample scarcity.
Zhu et al. (Thu,) studied this question.