Determination of alkyltrimethylammonium chlorides in river water by gas chromatography/ion trap mass spectrometry with electron impact and chemical ionization

This work describes a modified method to analyze alkyltrimethylammonium chlorides (ATMACs) in river water samples. The proposed method involves adding solid potassium iodide to water sample (pH adjusted to 10.0) as a counterion to enhance the extraction of ATMAC residues by dichloromethane liquid-liquid extraction. The iodide-ATMA⁺ ion pairs were demethylated to their corresponding nonionic alkyldimethylamines (ADMAs) by thermal decomposition in a GC injection port. The corresponding ADMAs were then identified and quantitated by gas chromatography/ion trap mass spectrometry (GC/ MS) in electron impact and low-pressure positive ion chemical ionization (PICI) modes. A relatively high abundance of ADMAs was detected at a demethylation temperature above 300 °C in the injection port. Experimental results indicate that the proposed method is precise and sensitive in ATMACs analysis and allows quantitation at ≤0.01 μg/L in 500 mL of the water samples. The enhanced selectivity of quasi-molecular ion chromatograms of C₁₂-C₁₈-ADMA, obtained using methanol PICI-MS, enables ATMAC residues to be identified at trace levels in environmental samples. Recovery of the ATMACs in various spiked water samples ranged from 70 to 94% while RSD ranged from 3 to 12%. The concentrations of total measured ATMAC residues in river water samples ranged from nondetectable to 1.24 μg/L.