A Gas-Liquid Chromatographic Method for Volatile Fatty Acids in Milk

Gas-liquid partition chromatography provided a means for a rapid and accurate analysis for the volatile fatty acids in milk.The chromatographic apparatus utilized a 6-ram.I.D. glass column 4 ft.long and packed with Celite 545 containing 25% liquid phase.The liquid phase consisted of silieone-stearic acid (95/5 w/w) mixture.The operating temperature of the colunm was controlled by use of a heating jacket through which glycerol could be circulated.Analysis for formic, acetic, propionic, butyric, valeric, caproie, and caprylic acids could be completed in 90 rain.This was achieved using a constant nitrogen gas pressure of 100 cm. of mercury and progressively increasing the colmnn temperature from 60-160 ° C. Quantitative recovery of a mixture of the seven pure acids was obtained in all trials.The water soluble-ether extractable acids were obtained from milk, using a modified Roese-Gottlieb procedure on acid filtrates.Recoveries of acids added to milk varied for each acid investigated.Recoveries of formic, acetic, and butyric acids were 57%, 86%, and 81%, respectively.Propionic, valerie, caproic, and capry!ic acids were recovered quantitatively.Replicate analyses revealed that the extraction procedure provided results reproducible within ---+ 5%.Gas-liquid partition chromatography is an extension of the theory and principles of gas chromatography to apply to relatively volatile liquids.Phillips (6) has reviewed the theory and applications of this technique for the separation of various organic compounds.James and Martin (2) introduced this procedure in 1952 for the separation and micro-estimation of volatile fatty acids, and for the methyl esters of fatty acids (3).Certain modifications in the James and Martin procedure for fatty acids were made by Van de Kamer et al. (7) to improve the separation and yields of volatile fatty acids from formic through dodecanoic in one-column analysis.Gas-liquid chromatography was used qualitatively by Jennings (4) to study the volatile compounds in starter culture distillate.Preliminary attempts in our laboratory to employ the gas-liquid chromatographic method of Van de Kamer et at.(7,8) resulted in unsatisfactory yields and incomplete resolution of some acids.Consequently, work was undertaken to develop a reliable method.After this study was completed, Hawke (1)reported the use of a different liquid phase for the volatile adds.He applied this method to quantitative analysis of volatile fatty acids in milk fat and applied gas-liquid chromatography of methyl esters for the analysis of nonvolatile fatty acids in milk fat.