Waters Silica Sep-Pak cartridges were evaluated for their performance in trapping short chain fatty acid ethyl esters. Liquid solutions of ethyl butyrate, ethyl valerate and ethyl caproate were injected onto cartridges. All the esters bound to the matrix and were eluted with four bed volumes of ethanol for ethyl butyrate and two bed volumes of ethanol for ethyl valerate and ethyl caproate. Samples of esters stripped with an air stream for 1 min and trapped on cartridges were found to vary by less than 8% for ethyl propionate, ethyl butyrate, ethyl valerate and ethyl caproate. Production of ethyl butyrate by Pseudomonas fragi CRDA 037 resting cells during biotransformation was efficiently evaluated using these cartridges. Variations between samples were found to be less than 10%.