You have partly answered your own question: You need a reference material to confirm that the analysis is not biased in some way and that you can recover entire concentration of Se.

Se is one of the more difficult elements to measure by ICPMS (for a number of reasons).

Some questions might help us solve your problem:

• How much He gas are you running? Perhaps your settings are not fully optimised for such low concentrations of Se?
• Which Se isotope(s) are you using? It may be a less abundant isotope, and knocked out by the He collision gas to below or near the detection limit of the instrument.
• Have you checked the limits of detection and uncertainty of measurement? Perhaps the He collision mode is just not sensitive enough.
• What is your calibration range? If your lowest calibrator is 50 ppB, then you don't really know when you start measuring noise below that, rather than "real" signal.

Have you tried spiking a sample of your bovine serum with several concentrations of Se (e.g 20, 40, 80 ppb). This might give you an indication of whether you can recover all the Se accurately through your acid digestion and ICPMS analysis. Hopefully the recovery will be the same for each gas mode.

Matthew Wheal

Thanks your comments.

It was difficult to purchase a CRM because it was not frequently analyzed.

In addition, the samples after digestion given to me are not a sufficient amount of sample to even spike with analysis for several confirmations.

In the end, I couldn't confirm it, and my analysis stopped.

The amount of He met the manufacturer's recommended amount, and he checked all isotopes, but most of the isotopes could not use the calibration curve.

Next time, I will compare them together using ICP-QQQ and try to use the internal standard together. It seems necessary to confirm whether this is a phenomenon caused by the characteristics of the serum sample.

Since you don't have a CRM, just try spiking the samples so you can check the Se recovery in different gas modes.