Toc 5000

Analytical techniques used to characterize AOM and membrane fouling included LC–OCD, FEEM spectrometry, and organic carbon analyzer. Raw water samples were filtered through a 0.45 µm filter in preparation for the analyses. The organic content of the samples was analyzed with a TOC analyzer (TOC-5000; Shimadzu, Japan). The UV-light absorption at 254 nm (UVA₂₅₄) and UV-Vis spectra were measured using a Shimadzu UV-1601 variable-wavelength spectrophotometer and a quartz cuvette with a 1 cm path length.

The acidified water samples were subsequently analysed for trace and major elements using an inductively coupled plasma-mass spectrometer (ICP-MS) (2007, Model: PerkinElmer Elan 9000) with an instrument limit of detection of 0.002 ppm for cadmium and 0.009 ppm for lead, whereas the samples for DOC and anions analysis were evaluated using the Shimadzu TOC-5000 without acidification. The leachate samples were digested using the wet acid digestion procedure. Pretreatment of 50 ml of leachate was done with 2 ml nitric acid, and 5 drops of 30% hydrogen peroxide were added in a closed bottle and placed in a constant temperature water bath at 60°C for 1 hour. The clear supernatant was filtered through 0.45 µm filters into plastic sample bottles and analysed for cations, whereas the samples for DOC and anions analysis were only filtered before analysis. The analyses were done over a period of three years, and mean values of the measurements have been reported. The major anions Cl⁻, NO₃⁻, and SO₄²⁻ were analysed at KTH, Stockholm, using a Dionex DX-120 ion chromatograph.

To prove the suitability of the prototype as a portable DOC analyzer, it was used during an environmental monitoring program on the water quality in Northern India. Overall, around 100 samples were taken from different sites and rivers in Uttarakhand, see Figure 2, during two sampling campaigns in October 2016 and October 2017. The water samples were taken from rivers and canals as well as from riverbank filtration and groundwater wells. All samples were filtrated (Chromafil^® GF/PET-45/25; Macherey-Nagel, Düren, Germany), acidified (pH 1.4, H₂SO₄, Merck, Darmstadt, Germany) on-site and shortly thereafter measured using the portable prototype. A comparative sample was taken, filtrated, acidified using HCl (pH 1.4, Merck, Darmstadt, Germany), refrigerated, and measured with a TOC-5000 (Shimadzu, Kyoto, Japan) as described above.

Soil moisture content was determined by the drying-weighing method. The pH of the organic and mineral soil samples was determined in a 1:2.5 soil/water suspension, and the pH of the litter sample was measured in a 1:10 litter/water suspension with a pH meter (Mettler Delta 340). Soil ${\text{NH}}_4^{+}$ and ${\text{NO}}_3^{-}$ were extracted with 2 mol L⁻¹ KCl solution and then determined by a flow injection automatic analyzer (Lachat Instruments, Mequon, WI). Soil dissolved organic C (DOC) and total dissolved N (TDN) were extracted with 0.5 mol L⁻¹ K₂SO₄ solution, and the concentrations of DOC and TDN in the extracts were determined by a TOC analyzer (TOC-5000, Shimadzu). Soil dissolved organic N (DON) was equal to TDN minus the sum of ${\text{NH}}_4^{+}$ and ${\text{NO}}_3^{-}$ . Soil available P was first adsorbed by anion exchange resin membranes and then extracted by 0.5 mol L⁻¹ dilute HCl, and the extracts were analyzed by the malachite green method (Veldhoven and Van Mannaerts, 1987 (link)). Total carbon (TC) and total N (TN) were measured by a C/N elemental analyzer (IsoPrime100, Isoprime).

In situ nutrient concentrations (i.e., NO₃ + NO₂, NH₄, PO₄) (water used for seawater medium) were determined using colorimetric methods (UV-1600 Spectrometer, VWR) as described in Valderrama (1995) . Chlorophyll a (Chl a) concentrations in the field were determined fluorometrically upon ethanol extraction according to Jespersen and Christoffersen (1987) as described in Bunse et al. (2019) (link). Samples to determine dissolved organic carbon (DOC) concentrations were taken at the LMO station during the time of sampling for medium. Additionally, samples were taken from each microcosm replicate immediately after the addition of organic compounds (T0). DOC concentrations were determined as follows, 30 mL of sample was filtered through 0.2 μm syringe filters (Acrodisk syringe filters, 32 mm, 514–4131, VWR), filled in MQ washed 60 mL EasY flasks (Nunc^TM Cell Culture Treated EasYFlasks^TM 25 cm², 156340, Thermo Fisher Scientific) and acidified with 448 μL of 1.2 M hydrochloric acid to a pH of ∼2. Flasks were stored in darkness at 4°C until analysis with a high-temperature carbon analyzer (Shimadzu TOC-5000) at the Umeå Marine Science Centre, Umeå, Sweden. Finally, DOC concentrations (one replicate per replicate enrichment culture bottle) were calculated as non-purgeable organic carbon and mean values per treatment calculated (n = 3).

The determination of the surface tension was performed at room temperature via the Wilhelmy plate method. All glassware and the platinum plate were rinsed with sulfochromic acid prior to the experiment to avoid interference of traces of residual compounds. A dilution series in distilled water ranging from 2.0 g/L to 0.01 mg/L was prepared and the surface tension was determined for each sample. The CMC values were determined as the concentration at which the minimal surface tension was reached when plotting the natural logarithm of the sophorolipid concentration against the surface tension. For sophorolipid lactone 5, the concentration of solubilized sophorolipid was determined with the TOC-5000 (Shimadzu) since this compound is not well soluble in water. With the bruto formula (C₃₄H₅₆O₁₄), the actual sophorolipid concentration could be calculated.

Non-purgeable total organic carbon (hereafter termed TC) in water samples was determined by measuring organic carbon after acidification with HCl (TOC-5000, Shimadzu, Kyoto, Japan). Total nitrogen (TN) in water samples was measured spectrophotometrically (Hitachi U-2000, Hitachi, Ltd., Tokyo, Japan) as nitrate after oxidation at high temperature. Total phosphorus (TP) in water and sediment samples was also measured spectrophotometrically after oxidative hydrolysis of organically bound phosphorus. Total carbon (TC) and total nitrogen (TN) in sediment samples was determined in freeze-dried and ash-free sediments by combustion with oxygen (elemental combustion system, Costech Analytical Technologies, Inc., Valencia, CA, USA).
The Jämtland lakes are generally more oligotrophic with low levels of total organic carbon compared to all Uppland sites (Table 1). However, the environmental variability, measured as coefficient of variation (CV) among sites, was not consistently higher in any data set but differed between environmental variables (Table 1).