By Anonymous on Friday, May 31, 2002 - 08:47 am:
Hi MS experts,
I am having trouble in getting repeatibility and linearity for 4-methoxyphenol using LC/MS/MS (ES-)method. I have a PDA connected in series before mass spec. I got good result on the PDA detector but not mass spec. My standard range is only from 1ppm to 12 ppm. Any suggestions on why the mass spec is not linear and reproducible?
By Jimmy on Friday, May 31, 2002 - 08:57 am:
We would need more info to provide reasonable suggestions. Phenols are ionized only at high pH (>9 or 10). Is your MP alkaline enough? Is anything coeluting in significant ammounts? Has the MP got enough buffer capacity? Is the analyte eluted at dead time? I haven't worked on phenols but I believe that they will have more retention on phenyl and PEG columns.
Best wishes
By Anonymous on Friday, May 31, 2002 - 09:19 am:
Hi Jimmy,
Thank you for the response. I am using a phenyl column with MeOH/water mobile phase. The mobile phase is not buffered. The retention time is close to dead time (about 2 minutes, dead time is about 1.2 min.). I will try a high pH mobile phase.
By Anonymous on Friday, May 31, 2002 - 10:40 am:
we use RP-18 for phenolics, with 0.4% acetic acid in the aqueous phase. We use either 64% aCN or 70% methanol as the organic, detection at 280nm, can get low ppm range easily with UV, peaks good.
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