Quantification of isoprene in coastal ecosystems by gas chromatography–mass spectrometry using cumulative headspace injections

Abstract

AbstractIsoprene is a biogenic volatile organic compound (BVOC), which is predominantly emitted by terrestrial plants but also from marine systems. However, the marine contribution to isoprene emissions is less understood due to the difficulty of measuring trace concentrations in seawater. Previous methods using “purge and trap” coupled with flame ionization detection and/or chemiluminescence have been developed, although these methods have limitations including large sample sizes, excessive manipulation, and potential interference from other BVOCs. These limitations could lead to overestimations or sample loss due to the high volatility and reactivity of isoprene. Here, we present an improved method for measuring isoprene in coastal marine ecosystems with elevated isoprene concentrations using cumulative headspace injection coupled with gas chromatography–mass spectrometry (GC‐MS). Sampling technique, preservation, and analytical conditions were tested and optimized using an analytical cycle time of 13 min. The analytical precision was 2.6% (n = 7), limit of detection was 15 pM, limit of quantification was 285 pM, accuracy based on recovery was 79% ± 2.8%, and reproducibility yielded a coefficient of variation of 15%. This method provides an improved way to measure isoprene from seawater using a simple sampling technique and fast, automated analysis, reducing isoprene loss through sample manipulation, and human error. This method meets analytical requirements to accurately measure isoprene at pM concentrations, which are typical of tropical coastal marine habitats. This method can also be adapted to measure other BVOCs in seawater such as dimethyl sulfide, providing a versatile method for marine research.