Dear all,

I would like to ask for your help regarding a problem with Agilent 7850 ICP-MS.

I am experiencing deviations in the internal standard recoveries (mainly Ge72 and Ir193) of up to +/-20% in He (5 ml/min He) and HEHe (10 ml/min He) modes. This affects calibratoin and entails failure of QC tests of As75, Se78 and Hg202.

Here are some clues:

1)Calibration, QC, and ISTD are prepared with the same blank solution 0.5% HNO3 + 1% HCl

2) Instrument routine maintenance is performed and cones and lenses are cleaned regularly.

3) If I exclude ISTD from calculations, the calibration dramatically improves and QC are within 10% tolerance.

4)Deviations occurs on Ir193 in He mode which is the ISTD of Hg202 (He mode), however Ir193 in no gas mode used for the detection of Pb208 does not suffer from the same deviations.

5) I tried to purge the Collision/reaction chamber with He 10 ml/min for 15 minutes before an analytical session, however it did not prevent the problem.

6) Since it happens on in He and HEHe mode, I thought that it is not a ISTD mixing and pumping issue.

Should I flow He to purge the collision reaction chamber for longer time before a session?

Is it normal than during tuning the signal for mass 89 is 2179 cps in HEHe mode and just 956 cps in He mode?

I'd be very grateful if you can share your opinions and experience with me and I am available for any further detail you might need.

All the best,

Andrea