Determination of volatile fatty acids in tofu wastewater by capillary gas chromatography with flame ionization detection: A Comparison of extraction methods

Abstract

Volatile fatty acids (VFA) are intermediate products during the anaerobic digestion process of complex waste. Accurate quantification of VFA is a useful measurement of the process. This study evaluated two extraction methods for gas chromatography determination of the following VFA: acetic acid, propionic acid, butyric acid, and valeric acid to find a simple and efficient preparation approaching on Green Analytical Chemistry methods. Tofu wastewater was used as the sample. The extraction was performed using diethyl ether and carried out either by vortex mixing or shaken by hand. The measurement was performed using gas chromatography with HP-INNOWax column and flame ionization detector. The linearity, precision, accuracy, limit of detection and limit of quantification were evaluated. VFA determination was linear at the concentration range of 5-500 μg/mL for all VFA. The precision of 2.59-12.63 % was obtained for both methods. The recovery of the fortified sample (10 μg-VFA/mL) was 75.33-98.31 % for vortex extraction and 99.81 to 103.80 % for shaken by hand extraction. Limits of detection and quantification of vortex extraction were 0.38-2.78 μg/mL and 1.06-3.03 μg/mL, respectively. Limits of detection and quantification using hand shaken extraction were 0.09-1.13 μg/mL and 0.55-1.61 μg/mL, respectively. Based on the high recovery and low limits of detection and quantification, shaken by hand extraction method can be used for rapid and accurate quantification of VFA.