Chromatography Forum

Hello all,

I have attempted to create a gradient elution that minimizes baseline drift at low levels as much as possible with our AS18 column but haven't had too much luck. I have posted previously about what I am trying to accomplish, but to summarize, I am trying to achieve a single run that can achieve fluoride, acetate, formate, nitrite, nitrate, sulfate, and phosphate in under an hour (ideally under 45 minutes).

At the levels that we analyze at, an isocratic elution would be the best route to a "clean" looking run. The problem is that phosphate elutes so much later than the other analytes and increasing the eluent concentration causes poor separation between fluoride, acetate, and formate.

I will detail our system below, but my question is: is there a better column suited to what we are trying to accomplish? We use the AS18 currently, but I have narrowed it down to AS11-HC, AS18-Fast, and the AS19 as other options. Will changing the type of column help the situation? Does anyone use any of the columns mentioned above?

Any information will be appreciated. Thank you in advance.

System: Dionex ICS-5000/ IC-6000
Column: AS18 4 x 250mm
EGC: EGC KOH 500 RFIC
Suppressor: ADRS 600
Injection Volume: 100µL

As-18 fast gets phosphate off the column in under 15 minutes but you won't be able to separate fluoride acetate and formate well. My RTs are 2.08 minutes fluoride, 2.18 minute acetate and 2.3 minute formate. I tried lowering the eluent on it and that doesn't help separate anions as well as it does on a regular as-18 column. In order to move sulfate around I increase the temperature, but that doesn't help with acetate or formate. I just looked at some published chromatograms from Fisher on the AS-11 4 mm and it looks pretty good to me.