Metals Testing using ICPMS

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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

1-2 minute period with sensitivity in the sub ug/L range for most elements. This means that the concentration of more than 60 elements can be determined quickly. Using this technique, WCAS offers a test which we call a "Metals Screen" to measure the concentration of over 60 elements in a sample. An example report appears below:

Sample: Acid Leachate
Metals Screen Report
Inductively Coupled Plasma - Mass Spectrometry


	`ppb`	`Detection Limit`		`ppb`	`Detection Limit`
`Aluminum`	`1660`	`0.7`	`Mercury`	`ND`	`0.1`
`Antimony`	`0.9`	`0.1`	`Molybdenum`	`ND`	`0.1`
`Arsenic`	`ND`	`0.1`	`Neodymium`	`2`	`0.1`
`Barium`	`19`	`0.1`	`Nickel`	`ND`	`0.3`
`Beryllium`	`0.2`	`0.1`	`Niobium`	`0.5`	`0.1`
`Bismuth`	`ND`	`0.1`	`Osmium`	`ND`	`0.1`
`Boron`	`ND`	`3`	`Palladium`	`ND`	`0.1`
`Bromine`	`ND`	`50`	`Platinum`	`ND`	`0.1`
`Cadmium`	`ND`	`0.1`	`Praseodymium`	`0.4`	`0.1`
`Calcium`	`9100`	`100`	`Rhenium`	`ND`	`0.1`
`Cerium`	`3`	`0.1`	`Rhodium`	`ND`	`0.1`
`Cesium`	`ND`	`0.1`	`Rubidium`	`0.8`	`0.1`
`Chromium`	`ND`	`1`	`Ruthenium`	`ND`	`0.1`
`Cobalt`	`ND`	`0.1`	`Samarium`	`0.3`	`0.1`
`Copper`	`0.8`	`0.2`	`Selenium`	`ND`	`1`
`Dysprosium`	`0.3`	`0.1`	`Silver`	`ND`	`0.1`
`Erbium`	`ND`	`0.1`	`Sodium`	`230`	`3`
`Europium`	`ND`	`0.1`	`Strontium`	`18`	`0.1`
`Gadolinium`	`0.3`	`0.1`	`Tantalum`	`ND`	`0.1`
`Gallium`	`0.6`	`0.1`	`Tellurium`	`ND`	`0.1`
`Germanium`	`ND`	`0.1`	`Thallium`	`0.8`	`0.1`
`Gold`	`ND`	`0.1`	`Thorium`	`ND`	`0.1`
`Hafnium`	`ND`	`0.1`	`Thulium`	`ND`	`0.1`
`Holmium`	`ND`	`0.1`	`Tin`	`ND`	`0.4`
`Iodine`	`ND`	`0.1`	`Titanium`	`6`	`0.2`
`Iridium`	`ND`	`0.1`	`Tungsten`	`ND`	`0.1`
`Iron`	`ND`	`50`	`Uranium`	`0.3`	`0.1`
`Lanthanum`	`2`	`0.1`	`Vanadium`	`0.9`	`0.2`
`Lead`	`1`	`0.1`	`Ytterbium`	`ND`	`0.1`
`Lithium`	`1`	`0.1`	`Yttrium`	`2`	`0.1`
`Lutetium`	`ND`	`2`	`Zinc`	`10`	`0.2`
`Magnesium`	`1400`	`0.4`	`Zirconium`	`3`	`0.1`
`Manganese`	`120`	`0.1`

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.

Some elements have reduced sensitivity and higher detection limits, the most problematic being iron (Fe). Because the plasma has a background of argon oxide (ArO, mass 56) which is an interference for the most abundant ⁵⁶Fe isotope, the less abundant isotope

⁵⁷Fe is used, leading to reduced sensitivity and higher detection limits (20-100 ug/L). One alternative for Fe is graphite furnace atomic absorption (GFAA), however this is not very advantageous since GFAA has a detection limit for Fe of about 10 ug/L coupled with many more potential interferences and experimental difficulties.

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.

For a quotation......

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