Identification of dissolved volatile metabolites in microbial cultures by membrane inlet tandem mass spectrometry

A membrane inlet tandem mass spectrometer is used for easy identification of volatile metabolites in microbial cultures. Filtrates of the cultures are without further purification placed into a measuring cell and introduced via a membrane inlet into a triple-quadrupole mass spectrometer. The samples are analysed with electron impact and chemical ionization mass spectrometry and tandem mass spectrometry. An extra dimension of separation is obtained by utilizing differences in response time due to differences in transport rates through the membrane. The following examples are used to demonstrate the technique. (i) Filtrates from cultures of three parasitic protozoa (trichomonads); two different strains of Trichomonas vaginalis isolated from humans and from Tritrichomonas foetus isolated from cattle were analysed. Indole was found in all samples; dimethyl disulphide was also present in cultures of the two organisms isolated from humans. (ii) The yeast Brettanomyces was grown in the presence of coumaric acid, ferulic acid, vanillic acid or syringic acid and the filtrate analysed for volatile products. In all cases ethyl acetate was found; coumaric acid biotransformation also gave 4-ethylphenol, whereas ferulic acid also gave 4-ethyl-2-methoxyphenol.