Requirements for water for LC-ESI_MS (quantitative analysis)

[chern_es]

Dear colleagues,

Could you, please, recommend a kind of water to use for LC-ESI_MS (quantitative analysis)?
I've heard opposite opinions: some people say - use deionized water with resistance more than 18 MOm; others say - don't do it, and suggest to use bidistilled water.
It is too inconvenient to us to buy HPLC-grade bottled water.

What do you think about it?

Best regards,
Elena

[Kostas Petritis]

Can you use Millipore or similar water purifiers, a lot of labs use those as a suitable alternative to bottle HPLC grade bottled water?

Other solutions might work, and at the end of the day it is your baseline and background at the m/z that you are analyzing that will determine if the water is of good enough purity (well... tab water won't work...). Another (sometime invisible) problem might be ion-suppression due to impurities

Try equilibrating a C18 column at 97% water for a couple of hours and then do a gradient to 80% ACN... Use different water sources for each run... you'll get a good feeling after that of what works and does not work...

[Hugo_Chav]

In my experience the biggest problem is not the source, Bottled gradient HPLC grade or Millipore are both fine, it is what happens to it after, Machine washing of reagent bottles, accumulation of dust and "bugs" growing, are bigger issues to manage. the most reliable way of working in my opinion is to buy bottled water, add any additives directly to the bottle, formic acid for instance, and run your chromatograph directly from this reservoir and discard it afterwards, with one caveat that water directly from a modern water purifier is better quality when it really counts, that is less liable to induce ion suppression.