BS EN 15936-2012 pdf download.Sludge, treated biowaste, soil and waste Determination of total organic carbon (TOC) by dry combustion.
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 dunng 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 8 Is dependent on expenence and practice, especially regarding the steps before the determination of TOC. Use of automatic dispensing units regarding removal of carbonates pflo 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 coulometnc 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.
If samples contain — depending on the accuracy of the method — negligible amounts of volatile compounds except water, the samples may be dried.
9 Procedure – Method A (Ind,r’ect method)
9.1 Determination
9.1.1 General
The mass of the test portion should be as large as possible and shall be chosen so that the liberated quantity
of carbon dioxide lies within the working range of the equipmenUcalibration.
9.1.2 Determination of the TC
The sample prepared according to Clause 8 is weighed into a suitable vessel (7.4). To minimize carbon blank values the vessel may be pretreated by heating (in a muffle furnace or the TC apparatus itself).
The sample is burned or decomposed in a flow of carrier gas containing oxygen (6.13).
The combustion temperature shall be high enough to convert all carbon completely to carbon dioxide. For samples containing carbonates, which are difficult to decompose, e.g. barium carbonate, the release of the carbon dioxide may be improved by increasing the temperature or by the use of modifiers, e.g. tin, copper.
The temperature range of commercially available instruments is between 900 °C and 1 500 °C.
During the combustion of reactive samples explosion or turning may be prevented by covering the sample with Inert material e.g. silica sand.
The carbon dioxide released during the analysis is measured using one of the detection methods infrared spectrometry. gravimetry, coulometry, conductometry. thermal conductivity detection, flame ionisation detection after reduction to methane, or other suitable techniques, and is expressed as carbon
9.1.3 Determination of the TIC
The sample prepared according to Clause 8 is weighed into the purging unit (7.3).
The system is closed gas-tight and flushed with carrier gas until no more carbon dioxide from ambient air is present. Then acid (6.12) is added and the carbon dioxide is stripped by purging or stirring andlor heating. The released carbon dioxide is transferred to the detector by the carrier gas.BS EN 15936-2012 pdf download.
BS EN 15936-2012 pdf download
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