title: The gas chromatographic determination of volatile fatty acids in wastewater samples: evaluation of experimental biases in direct injection method against thermal desorption method.
abstract: The production of short-chained volatile fatty acids (VFAs) by the anaerobic bacterial digestion of sewage (wastewater) affords an excellent opportunity to alternative greener viable bio-energy fuels (i.e., microbial fuel cell). VFAs in wastewater (sewage) samples are commonly quantified through direct injection (DI) into a gas chromatograph with a flame ionization detector (GC-FID). In this study, the reliability of VFA analysis by the DI-GC method has been examined against a thermal desorption (TD-GC) method. The results indicate that the VFA concentrations determined from an aliquot from each wastewater sample by the DI-GC method were generally underestimated, e.g., reductions of 7% (acetic acid) to 93.4% (hexanoic acid) relative to the TD-GC method. The observed differences between the two methods suggest the possibly important role of the matrix effect to give rise to the negative biases in DI-GC analysis. To further explore this possibility, an ancillary experiment was performed to examine bias patterns of three DI-GC approaches. For instance, the results of the standard addition (SA) method confirm the definite role of matrix effect when analyzing wastewater samples by DI-GC. More importantly, their biases tend to increase systematically with increasing molecular weight and decreasing VFA concentrations. As such, the use of DI-GC method, if applied for the analysis of samples with a complicated matrix, needs a thorough validation to improve the reliability in data acquisition.
authors.affiliation: Department of Civil ﻿and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul 133-791, Republic of Korea.
authors.forename: Md Ahsan
authors.initials: MA
authors.lastname: Ullah
authors.affiliation: Department of Civil ﻿and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul 133-791, Republic of Korea. Electronic address: kkim61@hanyang.ac.kr.
authors.forename: Ki-Hyun
authors.initials: KH
authors.lastname: Kim
authors.affiliation: Department of Civil ﻿and Environmental Engineering, Hanyang University, 222 Wangsimni-Ro, Seoul 133-791, Republic of Korea.
authors.forename: Jan E
authors.initials: JE
authors.lastname: Szulejko
authors.affiliation: ﻿Department of Environment & Energy, Sejong University, 98 Goon Ja Dong, Seoul 143-747, Republic of Korea.
authors.forename: Jinwoo
authors.initials: J
authors.lastname: Cho
mesh_terms: D002138:Calibration; D002849:Chromatography, Gas / Q000379:methods*; D004777:Environment; D005232:Fatty Acids, Volatile / Q000032:analysis*; D007267:Injections; D012722:Sewage / Q000737:chemistry*; D013696:Temperature
chemical_list: D005232:Fatty Acids, Volatile; D012722:Sewage
keywords: Heating mantle vaporization; Matrix effect; Retention time shifting; Volatile fatty acid; Wastewater