Improving the quality of 63Cu/65Cu ratio determination by ICP-QMS through a careful evaluation of instrumental performances

Abstract

An alternative validated analytical protocol for the determination of ⁶³Cu/⁶⁵Cu isotopic ratios via ICP-QMS is here proposed. Preliminary experiments and a careful evaluation of the instrumental performances have led us to propose a markedly different protocol from methods reported in literature: a modified bracketing method was chosen over the utilization of a long-term standard bracketing approach or the utilization of internal standards. As a result, accurate ratios with relative standard deviations as low as 0.025% can be obtained within an overall machine time (samples, blanks and standards) of 1 h per sample. Noticeably, this precision is only 2–5 times higher than the one attainable for ⁶³Cu/⁶⁵Cu ratio determinations with sector-field multi-collector machines. The required machine time is markedly lower than the one necessary for typical standard bracketing protocols (1 h vs. 2–4 h per sample, respectively). In contrast with internal standard based methods, the required machine time is definitely lower, but with our protocol no time consuming sample purification pretreatments are needed. The protocol has been validated and used for the determination of ⁶³Cu/⁶⁵Cu isotopic ratios on various copper minerals coming from historical mines spread along the Italian Apennines and Alps.