Chromatography Forum

I would like to analyse lactic acid in combination with other organic acids in water without derivating this compounds by GC-FID.
Is there anyone who has experience with this analyse or who has any suggestions?
At this moment I use a Aqua-wax column but Lactic acid doesn't appear.
Reason?

Helena,

You are trying to do one of the most difficult analyses in GC. The polarity of lactic acid is high and it will stick to any dirt or active surface in your G.C. It is much more difficult to analyze than normal straight chain acids like acetic and proprionic acids. The detector sensitivity for lactic acid is also lower than the other acids.

I got best results for this analysis using a packed column from Supelco (Carbopack B-DA with 4% Carbowax). One of the advantages of a packed column is that you can inject the samples directly on to the column-no place for the lactic acid to get adsorbed in an injection liner. Also, water produces a ton of vapour which can backflush from small capillary injectors.

I would consider doing this by HPLC-not sure about the comparative sensitivity but you shouldn't have as many problems.

Victor,
the lactic didn´t decarbonylate at the temps needed for this? What was the temperature?

I've used this published GC procedure; it uses derivatization but works good. One of the analytes detailed is lactic acid. "Simultaneous Determination of Alpha and Beta Hydroxy Acids in Personal Care Products by Capillary Gas Chromatography", J. Cosmetic Science, Vol. 53, March/April 2002, pp. 121-126

In addition to decarboxylation lactic acid can undergo oligomer formation at higher temperatures, dimer of lactic acid could also form cyclic by-product. If the sensitivity is not an issue I would use HPLC for these purposes. Check the following link-it describes separation of lactic acid and oligomer, which always present in lactic acid.

http://allsep.com/makeCmp.php?cmp=Cmp_156

Hi
Last year I also tried to analyse lactic acid in conjunction with other acid but I finally dropped as lactic acid peak appeared and disappeared from one injections to another one. Very bad reproducibility and repatibility achieved

HWM,

The column temperature used for lactic acid analysis was 175 degrees.

The retention time was higher than for butyric acid and I obtained only a single peak, although did not do MS to confirm absolutely that nothing had happened to the lactic acid. However, results were reasonable precise and gave linear calibration.

I always used ion chromatography. Excellent sensitivity.