Chromatography Forum

Dear Friends,

I have a question?

1. What is the limit of concentration you can minimally use for detection in ZQ4000 mass spectrometer from WATERS with ESI probe?

2. Do you weigh the samples or just take a bit and dissolve in the appropriate solvent and then dilute them?

3. Also is there a problem for analysing coordination compounds Does it spoil the ESI probe and what do you think is the best way to clean the probe after each injection to prevent carryover?

Are you just doing flow injection analysis to monitor a synthesis reaction or get a mass spectrum of a pure product?
I worked in a synthetic lab with an "open-access" setup and usually we'd just take a drop of the reaction mixture using a pasteur pipette, dilute it up to about 1 mL with methanol and/or water and inject it.

1) LOD is very variable depending on what sort of sample you are running and how it ionises. 1 pg/ul may be a practical limit though I'm sure Waters will quote much lower.

2) I'd definetly weight your sample so you know how much "a bit" is and at what level you get reasonable results and when you don't. Too concentrated is also a problem.

3) precipitated salts can be an issue - they may block your probe but are more likely to block your cone resulting in reduced sensitivity. You can try just running plain solvent afterwards which may clear the lines. This is unlikely to clean the cone. There are procedures in your manual (available from Waters website if you've lost it) for cleaning the cone.