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- Posts: 34
- Joined: Tue Apr 25, 2006 12:08 pm
Hello,
I am having problems to get a good sensitivity with an Esquire LC-MS (electrospray-ion trap).
I will explain a little what I am doing. I want to extract different acidic pharmaceuticals from sewage and river water and then analyse the extract with LC-MS. The extract solutions are 15 microlitres of 0.5M ammonium carbonate pH: 9.1. Then have added after different amounts (5 or 10 microlitres) of different solutions (acetonitrile, water, methanol or mixture) containing formic acid (5 or 10%). Then we injected into the LC-MS. The MS parameters were optimised with water-based solutions containing the analytes. The column is C8, 2.1 mm inner diameter. Flow rate 0.15 mL/min. We have tested different gradients mixing acetonitrile and 5 mM ammonium acetate, pH 4 adjusted with formic acid. E.g. we start with 10% acetonitrile for a minute and then we raised to 90% ACN in 10 min. We leave it for 4 minutes and then we decrease it again to 10% in a minute, stop time 25 min.
The problem is the ion suppression we get when we extract river-sewage water compare to for example distillated or tap water. The ion suppression compared to standard solution (0.5 mM ammonium carbonate) is enormous leading to very poor sensitivity. Is there anything we could do to improve the sensitivity?
Thanks,
I am having problems to get a good sensitivity with an Esquire LC-MS (electrospray-ion trap).
I will explain a little what I am doing. I want to extract different acidic pharmaceuticals from sewage and river water and then analyse the extract with LC-MS. The extract solutions are 15 microlitres of 0.5M ammonium carbonate pH: 9.1. Then have added after different amounts (5 or 10 microlitres) of different solutions (acetonitrile, water, methanol or mixture) containing formic acid (5 or 10%). Then we injected into the LC-MS. The MS parameters were optimised with water-based solutions containing the analytes. The column is C8, 2.1 mm inner diameter. Flow rate 0.15 mL/min. We have tested different gradients mixing acetonitrile and 5 mM ammonium acetate, pH 4 adjusted with formic acid. E.g. we start with 10% acetonitrile for a minute and then we raised to 90% ACN in 10 min. We leave it for 4 minutes and then we decrease it again to 10% in a minute, stop time 25 min.
The problem is the ion suppression we get when we extract river-sewage water compare to for example distillated or tap water. The ion suppression compared to standard solution (0.5 mM ammonium carbonate) is enormous leading to very poor sensitivity. Is there anything we could do to improve the sensitivity?
Thanks,
