881 compact ic pro

All
C-IC measurements were carried out using an ASC-240S autosampler and
an AQF-2100H combustion oven (Mitsubishi Chemical Analytech, Yamato-shi,
Japan). For absorption, a GA-210 absorption unit (Mitsubishi Chemical
Analytech) was used. Furthermore, an 881 Compact IC pro (Metrohm,
Filderstadt, Germany) with a conductivity detector was used for the
detection of chloride. A scheme of the whole setup is shown in the
Supporting Information (Figure S1). Table 1 comprises the detailed
experimental setup and parameters used for each measurement.
For all measurements, 20 mg of each silica gel obtained
from THF
extracts was weighed onto ceramic boats and were combusted at about
1000 °C for 18 min. The absorption solution consists of 300 mg/L
H₂O₂ (30% solution, Sigma-Aldrich, Schnelldorf,
Germany) in 10 mL of MilliQ water. As an internal standard, 5 mg/L
phosphate (1000 mg/L phosphate solution, Merck) was added.

Extracted permafrost filtrates were analyzed for anions by ion chromatography using a Metrohm 881 Compact IC pro with detection by suppressed conductivity. Anion determinations were performed using a Metrosep A Supp 7/250 column with 3.6 mM Na₂CO₃ eluent (0.8 mL/min) at 45°C. A complementary set of determinations were performed targeting organic acid anions using a Metrosep Organic Acids 250/7.8 column with 0.5 mM H₂SO₄ eluent (0.5 mL/min) at 30°C.
Soluble NH₄⁺, NO₃^–, and NO₂^– measurements were carried out using batch-automated spectrophotometry (Aquakem 250, Thermo Fisher Scientific, United States). Ammonium was determined using the Phenate method [United States Environmental Protection Agency (U.S. EPA) method 350.1]. Nitrite was determined by diazotization with sulfanilamide and nitrate was catalytically reduced to nitrite using soluble nitrate reductase in the presence of reduced nicotinamide dinucleotide (NADH; EPA Method 353.1). All samples were analyzed in duplicate. Final DOC, DIN, and SCFA data were corrected for dilution and gravimetric water content.

In total, 3.75 g of Na₂S·9H₂O were dissolved in 500 mL distilled water creating a standard solution and was stored at 4 °C (pH~10.2) in dark conditions. A daily solution was prepared from the standard solution at a sulfide concentration of 9–11 mg/L while keeping initial pH of 8.
For each experiment, the sulfide and sulfate concentrations were measured before and after irradiation. Sulfide was measured according to the colorimetric method [37 (link)]. The examined water sample was diluted by distilled water according to the expected sulfide concentration. A 2.3 mL water sample was inserted into a test tube containing 0.2 mL of a reagent mixture (0.5 g/L N,N-dimethyl-p-phenylenediamine + 0.75 g/L FeCl₃·6H₂O + HCl)). The solution was mixed for 20 min, which is the time required for full-color development, then the color is stable for many hours. Color intensity was measured at 670 nm by a spectrophotometer (Genesys 10uv scanning, Thermo Fisher Scientific, Madison, WI, USA). The colorimetric method was calibrated using the iodometric method [38 ].
Sulfate (SO₄²⁻) was measured using Ion Chromatograph (881 Compact IC pro, Metrohm, Switzerland), and in addition, for closing the sulfur balance, sulfite (SO₃²⁻) concentrations were measured by the iodometric titration method (4500- SO₃²⁻ [38 ]).