Optimization and validation of a derivatization method with boron trifluoride in ethanol for analysis of aromatic carboxylic acids in water

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Authors: Mette Kristensen, Peter Christensen, Jan H. Christensen


Gas-chromatography (GC) analysis of carboxylic acids is limited by the high polarity and low volatility of most of these compounds. Boron trifluoride (BF3) mediated alkylation reactions is one of the most commonly used derivatization methods for making carboxylic acids GC compatible. A semi-automated BF3·EtOH (ethanol) derivatization method was optimized for comprehensive two-dimensional gas chromatography high-resolution mass spectrometry (GC × GC–HR MS) analysis of carboxylic acids in solid phase extraction (SPE) extracts of oil polluted water. The optimal derivatization method were found to be with addition of 300 μL BF3·EtOH per 200 μL sample and reaction at 75 °C for 24 h. Derivatives of eight selected acids (aliphatic, mono- and di-aromatic) were stable over 12 h with relative standard deviations (RSDs) of 2.0–10.7 %, the derivatization method was repeatable (RSDs of 3.2–17.2 %), detection limits (DL) and limit of detections (LODs) was in the range of DL = 0.53–1.63 ppb and LOD = 0.19–2.51 ppb for pure acid standards, and DL = 0.18–3.41 ppb and LOD = 0.28–5.46 ppb for matrix matched acid standards. Finally, the method was validated on the acidic fraction of a mixed anion-exchange SPE of oil polluted water. Thousands of degradation products from parent alkylated polycyclic aromatic hydrocarbons (PAHs) and aliphatic hydrocarbons, such as aliphatic acids and mono-, di- and tri- aromatic acids were analyzed by the applied method and compound groups were tentatively identified.

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