Dear colleagues, I hope someone could help me. I have too high recoveries (over 150%) for internal standard in He mode: as the batch progresses, in each subsequent sample the recovery is higher and higher. In No gas mode everything seems ok, recoveries are around 100%. My ICP-MS is Agilent 7700x. Thank you in forward.
Your question is a little open ended at the moment. Perhaps you can elaborate with some additional information?
- What is the internal standard element (and concentration)
- What are your elements of interest?
- What is the sample type, and how have you prepared it for analysis? What acid(s) have you used and how pure/clean are they?
- How does the sample get from the vial to the nebuliser? What tubing or other materials might be interacting with the sample on the way?
Hi Milica
If standard mode is stable, then I would suspect the gas supply for the ORS. My first guess would be some residual air in the He-line, which washes out over time. In this case the sensitivities should stabilize at some point, but that may take several hours. I would check by flushing the He-line with a small flow rate (maybe 1 ml/min) over night and see if sensitivities drift again the next day.
Hope that helps,
Bodo
I have worked again few days ago, and everything was just perfect. Recoveries for internal standard have recovered :). It seems that day ago was not day for my ICP-MS :). The only thing that I did was prolonging the time of He flow 5 ml/min through collision cell (around 15 min) in stand by mode. Thank you for your suggestion. Bodo Hattendorf Warm greetings from Belgrade!
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