Cost-Effective Detection of Perfluoroalkyl Carboxylic Acids with Gas Chromatography: Optimization of Derivatization Approaches and Method Validation

Abstract

The reliable quantification of perfluoroalkyl carboxylic acids (PFCAs) in environmental samples like surface water by using gas chromatography (GC) remains challenging because the polar PFCAs call for derivatization before injection and problems involving the integration of sample pretreatment and derivatization procedures. Here we proposed a cost-effective method for the GC based determination of C4–C12 PFCAs in surface water samples by integrating solid phase extraction and PFCAs anilide derivatization. First, we assessed the performance of different PFCAs derivatization methods, namely esterification and amidation. Esterification was unable to derivatize C4–C6 PFCAs. On the contrary, amidation procedures by using 2,4-difluoroaniline (DFA) and N,N′-dicyclohexylcarbodiimide (DCC) could successfully transform all the PFCA analogs to produce anilide derivatives, which could be easily detected by GC. Then the reaction conditions in the amidation approach were further optimized by using orthogonal design experiments. After optimizing the instrumental parameters of GC, the limits of detection (LOD) of this derivatization method were determined to be 1.14–6.32 μg L−1. Finally, in order to establish an intact method for the quantification of PFCAs in surface water samples, solid phase extraction (SPE) was used for extraction and cleanup, which was further integrated with the subsequent amidation process. The SPE-amidation-GC method was validated for application, with good accuracy and precision reflected by the PFCAs recoveries and derivatization of triplicates. The method reported here could provide a promising and cost-effective alternative for the simultaneous determination of C4–C12 PFCAs in environmental water samples.

A Rapid Derivatization for Quantitation of Perfluorinated Carboxylic Acids from Aqueous Matrices by Gas Chromatography–Mass Spectrometry

“…Although this causes the standard preparation to be more laborious, there are significant benefits. The biggest advantage is correction for losses occurring during the N 2 evaporation step (Section S4 and Tables S2–S4), which has been reported across analytical methodologies even when the extract is not evaporated to dryness . In addition, allowing the standards to procedurally mirror more of the sample preparation provides better methodological error control during sample preparation.…”

“…While volatility is less of a concern for other alkyl derivatives, , they still have minimal intermolecular interactions imparted to facilitate selectivity in chromatographic separation. The more recent approach of phenyl derivatization methods such as benzyl, pentafluorobenzyl, or 2,4 difluoroaniline addresses the selectivity issue by introducing potential for phenyl–phenyl interactions between derivatives and stationary phases for the otherwise inert fluoroalkyl chains. To date, only 2,4-difluoroaniline derivatization has demonstrated the ability to separate and quantify C2 and C3 PFCAs, which requires a complex extraction process …”

Extraction and derivatization for perfluorocarboxylic acids in liquid and solid matrices: A review

“…The aim of the research of Li and Sun was cost‐effective detection of PFCAs using GC‐MS. They applied solid phase extraction and anilide derivatization for surface water samples 76 . However, the method is not simple.…”

“… 57 They used Empore™ strong anion exchange disks to extract PFCAs from groundwater collected from fire‐training facilities. The use of SAX, 76 WAX, 54 and C18 78 as SPE phases for PFCA has been described in the literature.…”

“…They applied solid phase extraction and anilide derivatization for surface water samples. 76 However, the method is not simple. The presented derivatization procedure is similar to this described above: pH adjustments, addition of NaCl and ethyl acetate, re‐extraction, washing, drying with Na 2 SO 4 , and evaporation under nitrogen.…”