Chromatography Forum

Hi,

I'm going to start using the LC-MS-MS to continue my forced degradation studies.

As far as I know I cannot degrade the samples using HCl or NaOH due to incompatibilities with the MS-MS. Can anyone suggest another method how to hydrolyse my drug since I need pH 1 and 14.

Also does anyone have any experience with forced degradation studies of herbal drugs. It seems that no matter what condition I am trying, the drug is not degrading and I am getting the same chromatographic profile throughout.

Thanks so much

Can you neutralize just before you inject the sample? Or are you looking for degradation in the analytical system?

If injecting 10ul or less of sample the buffering of the mobile phase should take care of the small amount of HCL or NaOH in the samples before they reach the source.

Yes I will be neutralising my samples.

My mobile phase is 0.1% Formic Acid and 0.01%TFA in water and Methanol, so it is not exactly a buffer system.

Do you think I can still run the samples on MS-Ms or do I risk damaging the MS probe due to HCL/NaOH

Yes I will be neutralising my samples.

My mobile phase is 0.1% Formic Acid and 0.01%TFA in water and Methanol, so it is not exactly a buffer system.

Do you think I can still run the samples on MS-Ms or do I risk damaging the MS probe due to HCL/NaOH

If you'll be neutralizing it, then your main concern is the [Na+] concentration. What kind of concentrations are we talking here?

A small injection that contains non-volatile electrolytes, followed by a long enough chromatographic run, is unlikely to cause any rapid accumulation in the source as long as you do regular maintenance anyway. Moreover, once you are sure of your method you can divert flow to waste until some point between the end of the void volume and the elution of your first peak. In RPLC you can expect most elemental ions to elute with the void.

I don't know much about degradation, but the most common acid or base induced reactions are hydrolysis. Maybe your compounds of interest are just very stable to hydrolysis. What about oxidation, reduction, photodegradation etc?

For example I was analyzing some water samples for several pesticides including aldicarb and I prepared a calibration in DI water with 0.1% formic acid. Aldicarb did not degrade in my calibration solution, but my spike into the water sample had very poor aldicarb recovery. If I waited an hour after spiking, it was totally gone. On a whim I scanned for aldicarb sulfoxide and found it eluting at an earlier time in the spike but not my standards. I then tried spiking our own local drinking water and found the same thing happening albeit at a much slower rate. Turns out that in chlorinated water, aldicarb oxidizes very easily.

You may be able to carry out whatever form of hydrolysis or degradation reaction you want by whatever method you want, but then afterwards isolate the product and target reactant by solid phase extraction (or liquid/liquid extraction). This will remove most if not all the Na+ if using NaOH and acid if using acid.

Without knowing what your compound is, or what you want to do to it exactly, it is hard to give solid advice.

Alp