3.2. Calibration and detection limits of IC and IC-ICPMS
We generated calibration curves with the IC in standard mode (without
chloride removal), and with the coupled IC-ICPMS setup with chloride
removal, using both the conductivity detector in the IC and the SEM
detector in the ICP-MS. In all cases, the data show good linearity over
the concentration ranges that were tested, with correlation coefficients
(r2) better than 0.999 (Fig. 3, 4). As shown in Fig.
3, the performance of the conductivity detector in the IC is not
negatively impacted by the presence of the Cl-removal setup. Good
linearity was obtained with and without chloride removal, as illustrated
here with phosphite and nitrate. This observation demonstrates that the
Cl-removal may also be useful for analyses of ions such as nitrate that
cannot be analysed by ICP-MS. Furthermore, it gives confidence that the
clean-up column does not introduce random error performs as expected.
Regarding detection limits, the coupling of the IC to the ICP-MS
resulted in significant improvement, as expected. In standard mode
without chloride removal (Fig. 3a), we were able to confidently quantify
phosphite peaks down to ca. 0.32 µmol/L (10 ppb P) using the
conductivity detector alone. With the IC-ICPMS setup and the SEM
detector in the ICP-MS, a resolvable peak was obtained for as little as
0.003 µmol/L (0.1 ppb P, Fig. 4a). Slightly lower concentrations may
still be detectable. Our results are thus similar to the detection limit
of 0.002 µmol/L reported by Ivey & Foster
(2005)[4], despite a significantly smaller sample
loop (37 µL instead of 800 µL). Reproducibility in our IC-ICPMS setup
was 13% at 0.032 µmol/L.