Copper Isotope Analyses Using Solution Nebulization And Femtosecond Laser Ablation-multiple Collector Inductively Coupled Plasma Mass Sepectrometry

An accurate and precise analytical method of Cu isotopic compositions was developed using solution nebulization (SN) and femtosecond laser ablation (fsLA) multiple collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Two candidate reference materials for the Cu isotope ratio studies were proposed for Cu isotope measurement using standard-sample bracketing method. The instrumental details were also discussed regarding to SN/fsLA-MC-ICP-MS analyses. The main achievements are as follows:1. Chemical digestion methods for rock standards, sulfides and native copper were established. Purification of Cu isotopes was developed using AG MP-1M Bio-Rad resin. The total procedure blank was less than 0.23 ng while the recovery was more than 99.84%. High-purity nitrogen was flown into the ion exchange column in order to improve separation efficiency about 3 times when the gas flow rate was 50 mL/min. The total separation time was reduced by 67%. and the recovery rate of Cu remained more than 99.96%.2. Accurate measurement of Cu isotopes using MC-ICP-MS was developed after careful optimization of the instrument parameters, acidity effect, concentration effect and matrix effect. The experiments revealed that the concentration difference between sample and standard affected Cu isotopic compositions up to 0.73%o, while the concentration difference needed to maintain less than 20% in order to keep the variation of Cu isotopes less than 0.04%o. The results of some international reference materials agreed well with published values within 2SD analytical uncertainties.3. Two reference materials (NWU-Cu-A and NWU-Cu-B) were prepared for Cu isotopes measurement based on the commercial available pure copper metal. The two candidate standard solutions were determined simultaneously in three different key laboratories to evaluate the homogeneity and Cu isotopic compositions relative to NIST NBS 976. The copper isotopic compositions (865Cu) of NWU-Cu-A and NWU-Cu-B were 0.91±0.03%o (2SD, n=42) and -0.05±0.03%o (2SD, n=49), respectively. The external precision of both standards were better than 0.05%o (2SD), which was consistent with the reported results of international laboratories within 2SD uncertainties.4. An in situ measurement of Cu isotopic compositions of solid sample was developed using a fsLA-MC-ICP-MS. Based on experimental results, the Cu isotope fractionation caused by fsLA could be ignored. The optimized laser ablation parameters were laser energy density 0.77 J/cm2-0.85J/cm2, laser frequency 5Hz, and scanning rate 1?m/s. The Cu isotopic compositions of fifteen analyses of NWU-Cu-A was 0.94±0.13%o (2SD, n=15, standard material was NWU-Cu-B and corrected to NIST NBS 976), which agreed well with the results obtained by SN-MC-ICP-MS.