Yes lactic acid is not volatile enough to be analyzed by GC. Infact, we have not been able to detect it in human foot odor volatiles so far and I believe this could be the reason. For its analysis probably one needs an LC or better LC-MS due to its polarity. But better still it can be derivatives to an ester, detected and quantified by GC although you have to contend with micro to nano scale chemistry!

There are difficulties quantifying difficult but obviously bioactive components like L-lactic acid, which is highly water soluble. A recent MS thesis online describes its GC-MS using readily available derivative-making  materials from Aldrich Chemical Co.  

Follow this and additional works at: http://commons.emich.edu/theses

Harrison, Charles, "Quantification of Short-Chain Fatty Acids in Cecal Material by Gas Chromatography-Mass Spectrometry" (2010).

Master's Theses and Doctoral Dissertations. Paper 277.  

In addition to pentafluoryl benzoyl bromide (PFBB), literature articles commonly report TMS derivatives being prepared when analyzing OH- fattyacids involving preparation of the fatty acid in an ester linkage to a trimethylsilyl group (13). TMS derivatization requires a greater reaction time (80oC/30 min) and an increase in temperature above ambient conditions. Through internal trials and replications of standard calibration curves, optimal ratios of derivatizing reagent, catalyst, and SCFA were determined and are reported in the Experimental section. Future directions of this project could lead to the incorporation of multiple SCFA analysis with one assay quantifying multiple chemical compounds. As reported in the literature, lactate is a SCFA that has known health benefits when present in the GI system. Therefore, the assay could be further developed to remove inconsistencies in the reaction and improve reaction conversions. This may be accomplished by replacing BSFTA with 1% TMCS with 10% TMCS.

Good work but for biological samples one needs to directly detect and quantify the lactic acid directly without derivatization especially when conducting EAG studies. Furthermore, the TMSX would react with many other components of the sample with OH, SH, and NR2 groups thus making the sample more complex! Combinatorial Chemistry! Furthermore, my experience in nanoscale chemistry of insect pheromone identification and synthesis discourages derivatization of biological samples. I still bet LC or LC-ESI-MS using RP column would be a better method of quantifying lactic acid in biological samples

I found a few relevant hits for this good question in PubMed using "lactic cid" malaria:

http://www.ncbi.nlm.nih.gov/pubmed/24967767

 Four syndromes demonstrating hypoglycaemia+hyperlactataemia were found: 1) paracetamol-induced acute liver failure, 2) severe malaria, 3) lymphoma and 4) glucose-6-phosphatase deficiency."

As well as

http://www.ncbi.nlm.nih.gov/pubmed/24200840

in "plasma and urine samples from five patients with severe falciparum malaria; five acids had increased concentrations in plasma"

David, the second website given by Istvan confirms what I have been saying all along. Thank you Istvan

I'm not a chemist but you may want to have a look at Benier and others (2000 and 2001) analyzing skin emanations. They were able to detect Lactic acid through conventional GC-MS in spite of the difficulty.Picking from the work of Benier, the Takken lab at Wagenigen university, Netherlands have evaluated Lactic acid as a synergistic attractant of Anopheles gambiae s.l.. The compound is now considered an active part of synthetic blends for trapping malaria mosquitoes (Kline et al 2007; Okumu et al 2010; Olanga et al 2010; Mukabana 2012). The effectiveness of these blends is currently being evaluated in relatively large field trial in Rusinga Island under the umbrella of Solarmal - a malaria project that seeks to reduce malaria transmission using odour-baited mosquito traps. This might be totally irrelevant. I just though I might add it here :)

I have Dr, Bernier's dissertation on my office shelf. We all agree that LA is present in and on people-breath, blood, skin and in other living animals.  This single difficult-to-analyze component has part of a good attractive blend since Fred Acree published the first definitive paper in Science in 1968 before GC-MS. Acree et al were catching female Aedes aegypti in olfactometers with LA and CO2.  Making these things plus feet/ammonia based materials work in the field is the real challenge!  Thanks for the new citations.

PS: We never had Anophelines to work with.