Automated Method for the Sensitive Analysis of Volatile Amines in Seawater

Methylamines are polar, volatile, and organic nitrogen-containing compounds. They are challenging to analyze, limiting our understanding of their occurrence and role within the marine nitrogen cycle. We describe an automated headspace solid-phase microextraction method, coupled with gas chromatography and nitrogen phosphorus detection (HS-SPME-GC-NPD), for analyzing methylamines in seawater. Three SPME conditions were investigated: temperature, equilibration, and extraction. The method was 6-24 times more sensitive to trimethylamine (TMA) than to dimethylamine (DMA) and monomethylamine (MMA). DMA and TMA were detected in small seawater volumes (2.5-10 mL), at volumes 100-400 times that previously reported. Detection limits of 19.1, 6.6, and 4.1 nM (nMol L^-1) for MMA, DMA, and TMA, respectively, were measured in 10 mL sample volumes. Sample throughput was 4-6 times greater than previously reported similar methods. According to the Blue Applicability Grade Index (BAGI) metric, the method was considered “practical” and scored 62.5. The method was used to measure methylamines in seawater samples collected from the Southern Ocean. DMA and TMA were detected at concentrations from < LoD-35 nM and < LoD-48 nM, respectively. This study offers a systematic and standardized method for MA analysis in seawater and can significantly advance understanding of their role in marine systems.