Hi,

I'm trying to identify some carboxilic acids (without nitrogen atom) by HPLC/MS. I have very low sensitivity with the HPLC/MS method that I'm working, and then the minor impurities (which should be also a carboxilic acids), can't be identified. Flow 1.0 ml/min, Mobil Phase pH 2.O/ACN (1:1)on Kromasil (C-18 15 x 4.6).

Does anyone any idea to help me.

Thanks

Basil

Basil,

What type of interface are you using? If you are using an API instrument, try bringing the pH up to around neutral and try running in the negative ion mode. I've used this approach successfully for low level (<100 ppb) for some carboxilic acid derivatives.

Good Luck

Joe

Thanks Joe,

I could work with ESI or APCI.
I've been working with ESI and positive mode.
The problem could be to separate the impurities if I change the pH of the mobil phase.

I accept your suggestions

Basil

Basil,

One further suggestion...it's more of a pain, but you can tee in an alkaline buffer prior to the MS interface (sort of a post-column derivatization type setup) and therefore run your separation under acidic conditions and still use negative ion for the MS. I'd use this as a last resort, from experience, but it can work if nothing else does. Good Luck.

Joe

IC-MS works very well for organic acids, with detection limits in the range of 0.5-2 ppb depending on the organic acid. Many organic acids are well separated on a Dionex AS11 column using hydroxide eluent. A suppressor removes the nonvolatile eluent and counterions, and minimizes signal suppression. I use a single quad in -ESI mode at 0.25 mL/min. The MS that I have can run SIM mode and Full scan at the same time so you can get maximum s/n for the target anions and also collect full scan information for the unknowns. I have used this for drinking waters, waste waters, physiological samples, geological core samples, drugs etc.