Speciation of Elements in Water Samples by HPLC-ICPMS

Riccardo Magarini, PerkinElmer (Italia), Milano, Italy

The elemental species distribution (chemical form) is important for environmental monitoring since the element form can determine toxicity, bioavailability, and potential for migration in the environment. Chromium and arsenic are environmental important elements which may exist in various forms are. For chromium, the trivalent form (Cr3) is considered a nutrient, while the hexavalent species (Cr6) is toxic.  For arsenic, the trivalent form (As3) is more toxic than the pentavalent species (As5), and both of them are much more toxic than organic As.

Speciation of Cr (As and Br) can be easily performed by HPLC-ICPMS, taking advantage from power of detection and selectivity of ICP-MS and separation capabilities of HPLC. The availability of dedicated HPLC-ICPMS chromatographic software makes this combination even more attractive and user friendly. However, Cr determination can be affected by spectral interferences, most critical are ArC⁺ and ClOH⁺ for ⁵²Cr⁺ and ⁵³Cr⁺.  Being carbon and chloride ions normally present in environmental waters, the Cr detection at low levels may be inhibited. These interferences can easily be removed by “cleaning” the sample ion beam with ion-molecule chemistry in a reaction cell. Over than this, the cell, located before analyser quadrupole, contains a quadrupole that can be optimised to prevent/reject unwanted by-products that may lead to new unexpected interferences. Cell design allows to use different gases, including reactive ones, to specifically target interfering species to be removed.

This lecture describes the usage of HPLC-ICPMS to measure both trivalent and hexavalent chromium in drinking waters by using a simple sample preparation. Detection is accomplished in DRC mode to eliminate the spectral interferences with a reaction gas, thereby allowing for Cr low-level determination, The goal is to present a suitable methodology for determining the range of concentrations encompassed by some new legislation. Some results are also provided for the speciation of bromine, where DRC mode is applied to confirm the presence of Br species.