Saturday, April 29, 2006

Sensitivity vs. Stability

As a result of some really sloppy behavior on the part of our instrument yesterday, we tore the whole front end apart, put it back together, and then tuned it back up from first principles. It was a kick-ass learning experience, even if it did take all morning, because when we tuned it back up, we tuned for stability instead of sensitivity. I haven’t actually done that before.

Sensitivity is all the rage these days. You’d think that the geological community’s ICP-MS scientists were a bunch of SNAGS at a speed dating festival, the way they constantly go on and on about their sensitivity, counts per ppm and limits of detection. But stability is also important. Especially in certain contexts.

Yesterday, for example, we were measuring lithophiles in basalt. This sort of measurement doesn’t require sensitivity- any triple-thumbed numbnuts could detect them. In fact, the dilution factor is generally increased to prevent excess detector wear. The errors on the elemental ratios are not count-rate limited; they are limited by the drift in relative sensitivity for the various elements. So we managed to address that really well, and everybody went home happy on Friday afternoon.

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