ICP-MS Sensitivity Optimization
Using an ICP-MS DRC machine, Nor noticed that after several months, the counts for some of the metals in his standard had dropped. The multi-element standard solution was expired, but not all of the metal counts had dropped. Some even increased over time. Nor wanted to know what might cause this phenomenon.
ICP-MS sensitivity as per atomic number is influenced by the sample argon flow rate (higher flows generally cause higher sensitivity for the lower atomic numbers) and the settings on the ion optics. Even though the voltages may be the same, the optics will change with time and need to be optimized on a regular basis. The use of a different nebulizer, even though it is made by the same manufacturer, can cause this difference.
The use of the same type, but different torch and/or spray chamber can also be a factor. When a new or different torch is used, alignment is very important. Even the peristaltic pump tubing will 'stretch with use' and change the overall sensitivities as well as the relative sensitivities.
Last but not least is the aging of the sampler and skimmer cones. As they age the overall sensitivity goes down. ICP-MS has many more parameters than ICP-OES that analysts must address. I can identify with the problems you are having and can only encourage you to keep checking and optimizing these parameters. I find this necessary on a daily basis. After several years of operating our ICP-MS, it still takes about two hours from the time I fire the instrument up to the time that I feel comfortable collecting data.
Thank you for contacting Inorganic Ventures and please feel free to call or email with any questions.
Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures & Fellow Chemist
DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question. Feel free to contact us to verify whether these suggestions apply to your unique circumstances.