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Measurement and Results - High background counts at mass 220 using ICP-MS

 
We operate a ICP-MS and last week I changed the sampler, skimmer & hyper-skimmer cones. Since then I have been unable to get the Background 220 counts to <1, the recommended value. The first set of cones I tried showed signs of excessive corrosion & 'peeling' of the nickel at the orifices, after using a 'mild' matrix - 2% HCl & a daily performance solution (1% HNO3). These cones were retired & a new set installed yesterday - same result. So I did an extended 'conditioning' of the cones overnight using a 25% tap water in 2% HNO3 solution, as advised by the ICP-MS manufacturer. This morning, I changed the pump tubes, cleaned the cones, allowed the instrument to stabilize before running a daily performance check, and the background counts before & after full optimization were the same, ~4 cps. Also, last week when the new cones failed, I put an old set back in & they were ok! Any thoughts or suggestions to help explain this behavior?
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admin Total posts: 529
Even though there are no spectral features at mass 220 there numerous factors can affect measured intensities at that mass, such as instrument parameters like lens voltages, rod offsets, etc., or sample introduction details like nebulizer type (cross-flow vs. micro-concentric). As the variable with respect to the sample introduction system in this case only appears to be the cones (we’re assuming all other things being equal), it’s possible that tuning the various ‘downstream’ instrument parameters such as the lens voltages, etc., might correct (and explain) the discrepancy.
Posted: 09/05/18 22:25:29

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