We have purchased a new Agilent 8900 ICP-MS instrument. We will be updating these pages over the next year.
Our instrument is an Agilent 8900 ICP-MS. It is capable of analyzing most elements in the periodic table any sample that can be put into aqueous solution, or ablated with a laser. Detection limits and analytical precision vary widely with analytical protocol, blank contamination, interferences, matrix composition, and isotope abundance, but ranges from <0.1 ppt (parts per trillion) to >100 ppb (parts per billion) in aqueous solution. Analytical relative deviation is typically <3%, 1σ.
Internal standards are used to correct for instrument drift during a run. You can choose any internal standard elements you want, but consider the following:
Internal standards typically used are:
If possible, all bottles, volumetric flasks, pipettes, and other things that hold the liquids should be plastic, not glass. Solutions should never be stored in glass.
We have used a wide variety of digestion containers, including graphite crucibles for LiBO2 fusions (note: not permitted with our present instrument), 17 ml and smaller Teflon Savillex® containers for low-pressure acid digestions, cheap polypropylene or polystyrene test tubes for easily dissolved samples like calcite or phosphate shells, and 30 ml Teflon Picotrace high-pressure digestion vessels.
Reagents should preferably be of "ultra high-purity" grade, not the commonly used "reagent grade". 18 MΩ deionized or sub-boiling distilled water should be used.
HNO3 is preferred because it generally causes the fewest problems with polyatomic ion interferences. A major exception is 28Si, where HNO3 increases the background from N2+ interference. HCl, HClO4, and H2SO4 result in in a variety of polyatomic ion interferences (e.g. ClO+, ArCl+, SO+). Many of these interferences can be enormously reduced or made irrelevant with proper use of the reaction cell. HF can be used so long as it is largely removed prior to analysis so it does not damage the glassware, or if the HF-resistant sample introduction system is installed.
Although clean room facilities are not strictly necessary for preparation of routine samples, it is extremely important to keep the work area clean, especially free of dust, including dust falling from above. Don't assume new plasticware is free of contamination, clean or test it. If necessary, Teflon digestion vessels should be cleaned under the same conditions under which dissolutions are done.
Use standards as similar as possible to the unknowns. Because of the linear response of the instrument over 9 or more orders of magnitude (ppq-ppm), use of a blank and one well-characterized standard is possible, though perhaps not wise. It is also wise not to use standards having element concentrations vastly different than the unknowns. Here is a list of solid standards we have.
Most elements, including the rare earths, seem to be stable in dilute acid solutions forever. Other elements are not stable, depending on the composition of the host solution. For example, elements such as Ti, Nb, and Ta tend not to be stable in most solutions, though a little fluoride stabilizes these. Time also allows contaminants in the storage containers to leach into solution, or elements in solution to stick to the container walls. In general, it is better to analyze samples quickly rather than waiting a long time
Certain elements are "sticky" in the ICP-MS sample introduction system. The offenders I have come across can include Li, B, platinum group elements, Ag, Au, Hg, Nb, Ta, and W. Some can be rinsed from the sample introduction system by extended (>1 minute) wash times between samples with ≥5% HNO3. Others can be washed out by adding different acids, such as HCl, if the element complexes well with chloride (e.g., many transition elements). Sticky sulfide-forming elements can be washed out with an L-cysteine solution.