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Station DO (mg·L− 1) Temp (°C) Salinity pH Chl a (μg·L− 1) DOC (μmol·L− 1) DFAA (μmol·L− 1) DCAA (μmol·L− 1) NO3− (μmol·L− 1) NO2− (μmol·L− 1) PO43 − (μmol·L− 1) NH4+ (μmol·L− 1)
Ship channel 8.7 18 32 8.08 NM NM 0.15 3.10 NM NM NM NM
T2 6.6 25.2 19 NM 0.82 258.3 NM NM 15.99 BD 0.11 1.97
NM: not measured.
BD: below detection limit (0.03 μmol·L− 1).
Table options
The peptide incubation procedure followed the protocol of Liu et al. (2010). Briefly, AZD8055 were incubated in 250 mL amber glass bottles at room temperature (24 °C) under dark. At each time point (0, 2, 6, 9, 21, 30, 45, 54 h), duplicate samples (1.5 mL) were taken out and filtered through 0.2 μm syringe filters (PVDF) for peptide and DFAA analyses. Samples were stored frozen at − 20 °C until HPLC–MS and HPLC analysis.
3. Results and discussion
3.1. Method optimization
3.1.1. Assessing different mobile phases for HPLC
Acetonitrile and methanol (mobile phase B) were compared to find an optimal choice for the AVFA detection due to their wide application in peptide measurement. With 10 mmol·L− 1 ammonium acetate as the mobile phase A, AVFA (20 μmol·L− 1) in nanopure water with an injection volume of 100 μL was tested with different B mobile phases. The HPLC gradient program for assessments was as described in the HPLC–MS protocol above, except RNA transcript the flow rate was 1 mL·min− 1. The AVFA peak occurred 2.3 min later in the methanol elution than in the acetonitrile elution (Fig. 2A, B). Since sea salt usually occurs at the beginning of HPLC chromatograms, the further away the sea salt peak is from the AVFA peak, the less likely is sea salt to be introduced to the MS. Therefore, methanol is a better organic solvent than acetonitrile for our application.