We have an API 3000 LCMS and we are experiencing high sodium conatamination in our MS. The sodium adduct is more abundant than our molecular ion. It appears to be in the source or MS. When I infuse a sample I see mainly the sodium adduct. I have done the normal cl;eaning and have changed the peak tubing in the source. Is there any other way to minimize the sodium in the system?

Thanks

Just some things to try, and you may have already tried these:

- You mentioned infusion. Are you sure the sodium isn't coming from your sample? Even standards will often have trace impurities. To eliminate this possibility, inject your compound onto a reverse phase column, and do a gradient starting at high aqueous and ramping up organic until your compound elutes. Acquire the data in full scan and see if the sodium adduct is decreased substantially. If so, then the sodium was in your sample. (This won't work if your compound isn't amenable to reverse phase).

- For infusion, if this is positive ESI, try adding ~ 0.1 to 1% acetic or formic acid to your sample, if you aren't already. For LC/MS, add acid to your mobile phase if you aren't already.

- If your water is from a purification system on-site, try using bottled HPLC water and compare the difference. Flush out all channels of your LC system with the HPLC water first.

- On the API-3000, try adjusting DP upward and see if this improves the ratio of MH+ versus MNa+. Or go through the usual optimization scheme with DP, FP, and EP on your MH+ ion if you haven't already, then see what your full scan spectra look like.

- Ask yourself if this compound is amenable to your ionization mode, especially if this compound is neutral or acidic and you are working in ESI positive.

If your sample contains sodium you may remove it using an Anion Suppressor as used in Ion Chromatography. Our Metrohm Suppressor Module has been used successfully in this way. It fits all instrument types.
For more information see:
http://www.metrohm.com/products/07/833/suppressor/833sup.html