The determination of trace elements in liquid samples such as seawater presents a number of challenges for Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The high dissolved solids content (approx. 3.5%) of seawater can supress analyte signal, cause interelement interferences and clog the interface sampler and skimmer cones.

The seawater sample can be diluted, but at the expense of detectability, as some elements of interest in the 5 to 50ppt (ng/L) range. An alternative is a sample preparation that can selectively preconcentrate trace elemets of interest while having much less affinity for major matrix components such as Na, Ca and Mg.

A chelating polymer resin called SPR-IDA (Suspended Particulate Reagent - Iminodiacetate) can be used for preconcentration/matrix elimination of seawater. The reagent consists of 10 microns diameter polymer beads derivatized with the chelating agent iminodiacetate. The beads are supplied as a 10% suspension in deionized water, and can be easily pipetted into a sample. The resin suspension aliquot is typically 0.1ml per 15mL of seawater sample.

After an aliquot of the resin suspension is added to the sample, the pH of the sample is adjusted to 8 and the resin is separated by centrifugation. The supernatant liquid is removed, and the resin is washed to remove more of the remaining unbound sample matrix. Nitric acid is then added to the resin to release the bound analytes and the acid extract analyzed by ICP-MS.

For more information please see the SPR-IDA Application Note or contact a CETAC Representative.