On-line chloride removal from ion chromatography for trace-level
analyses of phosphite and other anions by coupled IC-ICPMS
Abstract
Rationale: Ion chromatography combined with inductively-coupled
plasma mass spectrometry is an ideal tool for measuring low
concentrations of anionic species such as phosphite; however, the high
concentration of chloride and other anions in natural solutions may
negatively impact chromatographic separation and data quality.
Method: We developed an on-line mechanism of removing chloride
from the sample within the ion chromatograph, using an additional valve
and a separation column that transfers chloride to waste while phosphite
and most other anions are retained. We installed this system in a
coupled IC-ICPMS system (ICS6000 and Element 2 in medium resolution
mode) and determined linearity and detection limits. In addition, we
measured phosphorous species by NMR for comparison as an alternative
method for phosphite determination. Results: Chloride was fully
removed from the samples while phosphite was retained and could be
analysed by IC-ICPMS. Concentrations could be measured down to 0.003
µmol/L and possibly less with good linearity over the explored range (up
to 1.615 µmol/L; r 2 = 0.999). In contrast, the
detection limit by NMR was 6.46 µmol/L. Conclusions: The
on-line removal mechanism works well for simplifying sample matrices. It
removes the need for costly pre-analytical sample treatment with OnGuard
columns. We confirm that IC-ICPMS is the most powerful technique for
quantifying phosphite in natural solutions. The new Cl-removal method
may also be applicable to analyses of other anions.