ICP-MS7900 Accuracy Issues

Question

Hi, we are running samples on our ICP-MS7900 to determine zinc content of samples. Recently we have had issues with some samples coming back with low results (have cross references with another machine, and the sample is not the issue). However, some samples come back fine, whilst others are low, even within the same batch. We have performed maintenance, but are wondering whether there is anything else we could try to improve the accuracy of our machines results? 
 Cheers

Agilent · Answer

Hello zoeg , 
 Zinc suffers a lot from contamination. From my experience, sometimes the following occur: 
 1) Memory effects - is the rinsing time between the samples enough to clean out remaining Zn from samples in the batch? To check this, you can introduce some blank solutions as BlkVrfy between the samples so you can get a better look. 
 2) Check the standards - Zn standard may be contaminated (with more Zn than it should), reflecting in the determination of your samples. Do you have another Zn standard to run as a sample to check the accuracy, or a CRM? Besides, are you using a multielemental standard or are you mixing monoelemental standards to come to a final intermediary multielemental standard? If so, you should check each standard to see if Zn is coming from any monoelemental standard. 
 3) Have you tried running the same sample multiple times, and see the RSD between the final reads? This should give you some insight over sample/instrument stability. 
 4) Are you running other elements in the same batch? Does the problem occur with other elements? 
 5) Have you tried other Zn isotopes? I know they may be not as sensible as the m/z 66, but it is worth the try. 
 
 Hope this helps, Rodolfo

ICP-MS7900 Accuracy Issues

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