Screening Samples for Metals using ICPMS

Introduction

Inductively coupled plasma-mass spectrometry (ICPMS) can be used to screen samples for metals contamination.  In a typical scan of a sample in solution, data may be  collected for masses 5-250 amu over a 

How's it done?

In a typical test, a sample is put into solution usually by digesting or diluting in acid.  The sample solution is spiked with known concentrations of three elements (usually Sc, In, and Tb).  Standards of common elements, blanks, and the sample solution are then introduced to the ICPMS  The element concentrations in the samples are then determined one of two ways:   (1) for the elements that are  in the

 standards, the elements are determined quantitatively (within 15% for most) or (2) for the elements not in the standards, the elements are estimated (within 50%) by comparison with internal standard responses. Unlike many other spectroscopic techniques ICPMS has a fairly uniform response, so fairly accurate estimates can be made.

For more information on the analytical technique, click here.

Pros

Since each element has a unique isotope mass, interferences are usually minimal.  Since detection limits are in the sub ug/L range, even tiny samples (1-10 mg) can be analyzed with excellent detection limits.  This is a very efficient way to test expensive or rare samples like synthetic peptides or proteins, or even samples from ancient artwork. 

Only 2-5 mL of sample solution are needed.  Usually a minimum of 10 mL is requested so that duplicates, spikes, and dilutions can be analyzed.  Do you suspect metals contamination is causing a problem with your product?  This is an excellent method for solving this problem.

Some non-metallic elements are usually reported using this method: Br, I, and P.

Cons

High concentrations of elements that are predominant in the sample can cause interferences for other elements.  These are usually elements of neighboring masses, oxides, halides, argides of some elements, and doubly charged ions.  For example Ca based products have an interference for Ni from CaO, and carbon based samples have an interference for Cr from ArC.  All of these potential interferences are considered and flagged in your report.  Our systems have collision cells to minimize molecular ion interferences.

Some elements are not determined by this technique: gaseous elements, C, S, F, Cl, and the internal standard elements that are spiked (usually Sc, In, and Tb).   Some samples are very difficult to place in solution (e.g. silicates).   Alternatives such as X-ray fluorescence which do not require solutions may be considered. 

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Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group