Toc vcph analyzer

Concentrations of total organic carbon and total nitrogen were measured by the high-temperature catalytic oxidation (HTCO) method using a commercially available automatic TOC-V_CPH analyzer (Shimadzu, Japan). Samples were filtered through 0.45 μm filters and used for analysis. One blank deionized water and positive control of known TOC and TN concentration were analyzed along with the samples. The TOC-V_CPH analyzer with a TNM-1 add-on is routinely used in conjunction with a Shimadzu ASI-V autosampler in non-purgable organic carbon (NPOC) mode, following the methodology recommended by Shimadzu. For flow cytometric analysis on Accuri C6 flow cytometer (BD Biosciences, San Jose, CA), 700 μL of water samples were stained with 7 μL of SYBR Green I (1:100 dilution in DMSO) (Invitrogen, Carlsbad, CA), and incubated in the dark for 10 min at 35°C before measurement. Where necessary, samples were diluted accordingly to achieve less than 4000 events/s at a pre-set flow rate of 35 μL/min.

Samples for measurements of various ions (F⁻, Cl⁻, SO₄²⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺), dissolved organic carbon (DOC) and total nitrogen (TN) were gathered in 125 mL low-density polyethylene (LDPE) bottles after being filtered from the water through 0.45 μm PES syringe filters and stored at −20 °C until laboratory analysis [57 (link)]. Samples for dissolved inorganic carbon (DIC) measurements were gathered in 125 mL brown, gastight, glass bottles (precleaned using ultrapure water). To prevent biological degradation and photodegradation, DIC samples were poisoned with a 0.2% saturated HgCl₂ solution and stored at 4 °C in the dark [51 (link)]. DIC, DOC, and TN were analyzed with a SHIMADZU TOC-VCPH analyzer (Shimadzu Corp, Kyoto, Japan). The pH and conductivity of sediment were determined using a soil parameter meter (STEPS COMBI5000, Nuremberg, Germany) with a sediment/water (1:5) suspension. The sediment moisture content was gravimetrically measured by drying the 5 g sediment samples with an oven to a constant weight at 105 °C. Approximately 50 g homogenized sediment was freeze-dried with a Labconco FreeZone 2.5 A freeze-dried system (Kansas City, MO, USA), and then sieved by 100 mesh sieves to analyze the total organic carbon (TOC). Finally, we analyzed the TOC of the sediment with the SHIMADZU TOC-VCPH analyzer (Shimadzu Corp., Kyoto, Japan).

Duplicate samples for DOC measurements were unfrozen at room temperature, acidified with 18 μL of phosphoric acid (H₃PO₄; pH < 3), and analyzed in triplicate by high-temperature catalytic combustion on a Shimadzu TOC-VCPH analyzer with an ASI-V auto-sampler. All inorganic carbon and purgeable organic carbon was removed by a sparging process of acidified samples.