Low but stable Internal standard recovery on ICPMS 7900

Is it possible that you do not have the same matrix in your rinse and the standards? It seems to me a matrix issue. Otherwise you would have a random pattern or a continuous up/down drift, if there was an issue in your sample introduction. ISTD% recovery will be calculated against the calibration blank, so you might measure the calibration blank multiple times at the beginning, to see if there is an issue in your uptake time settings. Afterwards you can switch between different versions of the calibration blank in the data analysis to see the difference. Keep in mind that you will need to configure only one calibration blank at the end. So, you can define the other cal. blank measurements as rinse or sample.    

I checked every single point you mentioned above and finally found out the blank I was using was contaminated in the preparation lab somehow. So we prepared a new batch and everything is back now. Thanks again

I checked every single point you mentioned above and finally found out the blank I was using was contaminated in the preparation lab somehow. So we prepared a new batch and everything is back now. Thanks again

Thanks for knowing us the solution. Have fun with the ICP-MS. Cheers.