Tuesday, August 15, 2006

Unheard of ICPMS drift: Rabbit Pump Drift

Fellow mass spectrometerists, check this out. I'm running some calibration standards and all the sudden, from the 100ppb to the 200ppb, internal standard recovery changes from 100% to 80%. Naturally thought it was sample introduction; checked for clogs, changed cones, changed to new nebuliser, still same drift, sometimes after 5 cups. Then it eventually, 5 cups or so, it kind of creeps back up around 100%.

Today, I was looking at the real time display, in deep thought while I watched the 115In and 209Bi signal intertwine bouncing across the 20 in. flat screen when I figured it out. I accessed the accessory window and switched the peristaltic pump into rabbit mode[1]. Sure enough, the signal drops, probably around 80%, but just going off counts per second at the time. Let it equilibrate and switch it back to regular pump speed, 24%. Oh, man, took like 3 or 4 minutes for the counts to get back up to where they were before rabbit pump.

Edited ACL script, no rabbit pump, calibrated fine, loaded samples, got to name a new type of drift: Rabbit Pump Drift.

I also named Seesaw Drift, this is when the low mass internal standards drift up while the high mass internal standards drift down, or the other way around.

[1] This is what the software that runs the ICPMS calls max speed pumping. Good for washing the probe during rinse.

1 comment:

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