I have been using ion exclusion chromatography (ICPAK column with 1mMol HCL at 1 ml/min) to quantitative organic acids in samples of ground water.

In my D-Lactate standards (95% purity) there has always been a mysterious peak that elutes 1 minute (RT 6.3) before that peak representing Lactate acid (at RT 7.9). This peak is absent in standards made of L-Lactate (97% purity), in which one peak at RT 7.9 occurs. This peak at RT 6.3 is exaggerated in reagent grade mixtures that claim to contain equal amounts of each enantimer. These mixtures claim to be a certain purity, however % recovery of lactic acid from this mixtures has been as low as 60%.

The reason for my concern is that I have been finding significant peaks at RT 6.3 in the samples I have been analyzing and I would like to identify this mystery compound. Lactate is almost always present in such samples.

The most significant peak at RT 6.3 I have found is in samples where polylactate is being degraded. Is it possible that this mysterious peak is a lactate dimmer? Or is it possible that my column is separating L and D lactate at different retention times?

I’ve been wrestling with this problem for quite a while, and any input you have would be greatly appreciated!

Carlie

What's the wavelength? have u ever tried mutiple wavelength on both D- and L- lactate?

Right now we only use a conductivity detector, I might be able to borrow a UV detector if you believe it might shed some light on my problem. I'm relatively new to IC (just graduated from college) so forgive me if I sound like I don't quite know what I’m talking about... but you would expect D and L lactate to absorb differentially at different wave lengths? I can always take the different fractions from the IC to a UVvis to investigate.

Anyway you're input is GREATLY APRECIATED!

Carlie

You could have a lactate dimer as that does happen, but the environment has to be right. Usually an anhydrous or low water environment would be needed. Otherwise, the lactic acid could oxidize to pyruvic acid, which would have a greater extinction in the low UV than lactic acid due to the keto-group. FWIW, in my experience with ion exclusion, pyruvic acid does elute before lactic acid as well.

Best of luck!