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

Abstract

Isoprene 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.

Heat stress decreases the diversity, abundance and functional potential of coral gas emissions

“…Isoprene concentrations were analysed using a GC‐MS (Agilent Technologies 6890N, 5973N) fitted with a Gerstel multipurpose sampler (MPS 2XL) as detailed in Hrebien et al. (2020). Briefly, from each vial, 1 ml of headspace was cumulatively extracted and injected onto a Tenax liner, kept at 20°C, three times.…”

“…Nubbins were removed from their epoxy holds and placed in 100 ml amber crimp cap vials (Chromalytic Technology) with 70 ml of water from the aquaria and sealed with PTFE/White Silicone septa caps (Agilent Technologies Pty Ltd) before adding 300 µl of saturated mercuric chloride solution (AJAX Chemicals). Isoprene concentrations were analysed using a GC-MS (Agilent Technologies 6890N, 5973N) fitted with a Gerstel multipurpose sampler (MPS 2XL) as detailed in Hrebien et al (2020). Briefly, from each vial, 1 ml of headspace was cumulatively extracted and injected onto a Tenax liner, kept at 20°C, three times.…”

Mangrove Creeks Are a Sink for Isoprene—A Functional Link Between Ecosystems

“…For isoprene, 70 mL was syringed from the Schott bottle into 100‐mL amber glass sample bottles filling from bottom up, ensuring no bubbles and crimped with Teflon septa crimp caps (PTFE/S, Agilent Technologies). The samples were poisoned with 150 µL 8% solution of HgCl 2 to cease any enzymatic activity and stored in the dark at 4°C (Hrebien, Deschaseaux, Eickhoff, et al., 2020). For DOC, 30 mL was filtered through precombusted GF/F filters into 40‐mL glass screw top bottles preacidified with 100 µL of 85% phosphoric acid.…”

Coral reefs as a source of climate-active aerosols

“…Seasonal peaks in phytoplankton biomass are usually found during the summer wet season when fluvial nutrient loads to the inshore GBR are high ( Gabric, Hoffenberg & Boughton, 1990 ; Brodie et al, 2007 ). Given the remote location and vast size of the GBR, seasonal shifts in stress-induced emissions of DMS from corals, and other volatile organics such as isoprene from reef sediments ( Swan et al, 2016 ; Hrebien et al, 2020 ), may be driving the increase in aerosol in spring and summer.…”