| Abstract: |
The capabilities of Cu isotope ratio measurements are often restricted by the small volumes of sample
available and/or their low Cu concentration. In this work, an analytical approach was developed for
performing Cu isotopic analysis via multi-collector ICP-mass spectrometry (MC-ICP-MS) at ultra-trace
level using Ga as an internal standard for mass bias correction. The minimum concentration of Cu
required for accurate and precise isotope ratio measurements was established to be 20 mg L-1 with wet
plasma conditions and 5 mg L-1 with dry plasma conditions. The use of Ga as an internal standard for
mass bias correction provided several advantages compared to Ni, i.e. improved internal precision on
d65Cu values and lower blank levels. Ga can also be used at a 4-fold lower concentration level than Ni.
However, in wet plasma conditions, the signals of 36Ar16O2
1Hþ and 40Ar15N16Oþ interfered with the signals
of 69Gaþ and 71Gaþ, respectively, while in dry plasma conditions, realized by the use of a desolvation
unit, 69Gaþ suffered from spectral interference from 40Ar14N2
1Hþ. These interferences were resolved by
using medium mass resolution. For validation purposes, the approach was applied to commercially
available blood and serum samples. The d65Cu values for the samples measured at a concentration level
of 5 mg L-1 Cu and 5 mg L-1 Ga using dry plasma conditions were in good agreement with those obtained
for isotope ratio measurements at the “standard” concentration level of 200 mg L-1 Cu and 200 mg L-1 Ni
using wet plasma conditions. In addition, the d65Cu values obtained for micro-samples of serum/blood
(volume of 100 mL) were in good agreement with the corresponding ones obtained using the “standard”
volume for isotopic analysis (500 mL). |
