BS EN 15936:2012 pdf download – Sludge, treated biowaste, soil and waste — Determination of total organic carbon (TOC) by dry combustion
The TIC is determined separately from another sub-sample by means of acidification and purging of the released carbon dioxide. The carbon dioxide is measured by one of the techniques mentioned above. Alternatively, for soil the total organic carbon content may be calculated by determining the total carbon content and subtracting the carbon present as carbonate, which can be determined according to ISO 10693 (volumetric method).
4.2 Method B (direct procedure) In this procedure, the carbonates present in the sample are previously removed by treating the sample with acid. The carbon dioxide released by the following combustion step is measured by one of the techniques mentioned in 4.1 and indicates the TOC directly.
4.3 Applicability of Methods A or B Methods A and B have the same applicability for the determination of TOC and/or the determination of the TIC to TOC ratio. In samples with relatively high inorganic carbon contents method B should be applied. Method B may lead to incorrect results in the following cases:
the sample contains volatile substances that evaporate during the acidification (e.g. volatile hydrocarbons from sludge of oil separators);
side reactions between the sample and the acid take place (e.g. decarboxylation, volatile reaction products). NOTE The quality of results of Method B is dependent on experience and practice, especially regarding the steps before the determination of TOC. Use of automatic dispensing units regarding removal of carbonates prior to determination of TOC may improve the performance of Method B. 5 Interferences Volatile organic substances may be lost during sample preparation. If necessary, the carbon content resulting from volatile organic substances shall be determined separately. Depending on the laboratory experience with samples containing high amounts of carbonate the procedures may lead to unreliable TOC results if the TIC to TOC ratio is very high (e.g. ≥ 10). Depending on the detection method used, different interferences may occur, for instance:
the presence of cyanide may interfere with the coulometric detection of TIC by modifying the pH value (dissolution of HCN);
high content of halogenated compounds may lead to an overestimation of TOC when coulometric detection is used; in some cases the classical silver or copper trap can be insufficient to absorb all halides. When present, elementary carbon, carbides, cyanides, cyanates, isocyanates, isothiocyanates and thiocyanates are determined as organic carbon using the methods described in this European Standard. An interpretation of the measured value may therefore be problematic in cases where the sample contains relevant levels of the above-mentioned components. If needed, these components shall be determined separately by means of a suitable validated method and be recorded in the test report. Elementary carbon, determined separately, may be subtracted if required for the sample. If this is done this shall be reported by the laboratory.
6 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified.
Hygroscopic substances shall be stored in a desiccator.
6.1 Calcium carbonate, CaCO 3 .
6.2 Sodium carbonate, Na 2 CO 3 , anhydrous.
6.3 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na 4 -EDTA · 4 H 2 O
(C 10 H 12 N 2 O 8 Na 4 · 4 H 2 O), heated at 80 °C for 2 h.
Other forms of Na 4 -EDTA hydrates may be used if the water content is exactly known. In these cases, the composition of the control mixtures has to be recalculated accordingly (see also 6.10 and 6.11).
6.4 Potassium hydrogen phthalate, C 8 H 5 O 4 K.
6.5 Acetanilide, C 8 H 9 NO.
6.6 Atropine, C 17 H 23 NO 3 .
6.7 Spectrographic graphite powder, C.
6.8 Sodium salicylate, C 7 H 5 O 3 Na.
6.9 Aluminium oxide, Al 2 O 3 , neutral, granular size < 200 µm, annealed at 600 °C. 6.10 Control mixture A prepared from sodium carbonate (6.2), Na 4 -EDTA · 4 H 2 O (6.3) and aluminium oxide (6.9) in a mass ratio of 2,34:1,00:1,97. The mixture shall be homogenized. It should contain 50,00 g/kg TIC and 50,00 g/kg TOC (e.g. 44,13 g of sodium carbonate, 18,83 g Na 4 -EDTA · 4 H 2 O, 37,04 g of aluminium oxide).