| Abstract: | The method after Strickland and Parsons is modified for fresh water as follows: filtration on glass-fibre paper, oxidation with K2Cr2O7 in cone. H2SO4 for 2 h at 130 °C, dilution to 2.5 times the volume by aqua dest., centrifuging-off of the turbidity and extinction measurement at 445 nm against the blank value, the sample solution being balanced to the transmission of 100% (extinction = 0). Here, the following calibration line holds for the concentration C and the quantity of oxidation solution Ox: C = E1cmc · 0.162 · Ox, C in mg filter. The oxidation solution contains 4.8 g K2Cr2O7 as dissolved in 20 ml aqua dest. and made up with conc. H2SO4 to 11. With 5 ml of this solution one is able to determine 0.05 … 1 mg C/filter. Calibration is performed with 125 mg/l glucose solution. Comparative investigations have shown a good agreement with elementary-analytically obtained measured values. The occurring errors have been determined mainly by sampling. In the range of very small values we have to take into account a blank value of the filter due to the adsorption of dissolved organic substances on the filter. |
