Samples were filtered straight from Niskin bottles following established protocols for trace-metal clean sampling (Sample handling protocols for GEOTRACES cruises).
Samples for DOC concentration were acidified to pH 2.5 and analyzed by high-temperature combustion on a Shimadzu TOC-L. DOC was calculated as the mean of between three and five injections using a six-point standard curve.
Lignin-derived phenols were determined following Yan and Kaiser (2018; Anal. Chem), and Yan and Kaiser (2018; Analytica Chimica Acta). Briefly, C18 extracts were redissolved in 200 μL of 1.1 mol L−1 argon- sparged (10 min) NaOH in a 400 uL Teflon vial (Savillex Corp) and amended with containing 500 mg CuO, and amended with 10μL of10 mmolL−1 CuSO4 and 10μ L of 0.2 molL−1 ascorbic acid. Oxidation was at 150 C for 120 minutes. Following oxidation, the samples were spiked with with a surrogate standard mixture of p- hydroxybenzoic acid-13C7, vanillin-13C6, and syringaldehyde-13C6 and acidified to pH ≈ 2.5 with 6 mol L−1 sulfuric acid in the reaction vials. Clean-up of samples was performed with Waters HLB cartrides and final sample eluates were dried under ultra-high purity argon. Phenols were quantified by liquid chromatography/electrospray ionization-tandem mass spectrometry using a five-point calibration curve bracketing the concentration range. Quantified phenols (TDLP included vanillin, acetovanillone, vanillic acid, syringaldehyde, acetosyringone, syringic acid, coumaric acid, ferulic acid, p-hydroxy-benzaldehyde, p-hydroxy-acetophenone, and p-hydroxy-benzoic acid.
Samples were filtered straight from Niskin bottles following established protocols for trace-metal clean sampling (Sample handling protocols for GEOTRACES cruises)
Samples for DOC concentration were acidified to pH 2.5 and analyzed by high-temperature combustion on a Shimadzu TOC-L. DOC was calculated as the mean of between three and five injections using a six-point standard curve.
Lignin-derived phenols were determined following Yan and Kaiser (2018; Anal. Chem), and Yan and Kaiser (2018; Analytica Chimica Acta). Briefly, C18 extracts were redissolved in 200 μL of 1.1 mol L−1 argon- sparged (10 min) NaOH in a 400 uL Teflon vial (Savillex Corp) and amended with containing 500 mg CuO, and amended with 10μL of10 mmolL−1 CuSO4 and 10μ L of 0.2 molL−1 ascorbic acid. Oxidation was at 150 C for 120 minutes. Following oxidation, the samples were spiked with with a surrogate standard mixture of p- hydroxybenzoic acid-13C7, vanillin-13C6, and syringaldehyde-13C6 and acidified to pH ≈ 2.5 with 6 mol L−1 sulfuric acid in the reaction vials. Clean-up of samples was performed with Waters HLB cartrides and final sample eluates were dried under ultra-high purity argon. Phenols were quantified by liquid chromatography/electrospray ionization-tandem mass spectrometry using a five-point calibration curve bracketing the concentration range. Quantified phenols: TDLP included vanillin, acetovanillone, vanillic acid, syringaldehyde, acetosyringone, syringic acid, coumaric acid, ferulic acid, p-hydroxy-benzaldehyde, p-hydroxy-acetophenone, and p-hydroxy-benzoic acid.
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