BS ISO 20236:2018 pdf free
BS ISO 20236:2018 pdf free.Water quality一Determination of total organic carbon (TOC)
Interferences with the determination of TOC or DOC and TNb or DNb can arise from memory effects.Replicate injections are necessary (see 10.4.1).
Detergents, oils and fats can influence the surface tension of the sample, causing erroneous data. A dilution of the sample can reduce such risk.
Samples with extreme pH values, highly buffered samples and samples with high salt contents can cause interference. Seek advice from the manufacturer to solve these interferences.
Suspended material can lead to a loss of quality of the analytical result. If a homogenized sample containing suspended material produces results obtained from replicate measurements that deviate by more than 10 %，an accurate TOC or TNb result cannot be obtained on the sample.
Inorganic carbon (e.g. CO2 or ions of carbonic acid) present in the sample interferes with the determination of TOC or DOC. Inorganic carbon is removed by acidification and purging with a gas that is free from CO2 and organic compounds prior to the TOC or DOC determination (see 10.4.2.2 and 10.4.2.3).
NOTE 1 Alternatively, the differential method determining the TC and TIC separately can be applied (see Annex A). The TOC can be calculated by subtracting TIC from the TC. This calculation leads to correct results only as long as carbon monoxide, cyanide, cyanate and thiocyanate are present with negligible concentrations.
NOTE 2 Purgeable organic carbon substances, such as benzene, toluene, cyclohexane and chloroform,can partly escape upon stripping (see 10.4.2.2 and 10.4.2.3). In the presence of these substances, the TOC concentration can be determined separately, for example by applying the differential method (see Annex A).High loads of dissolved or total organic carbon (DOC or TOC) can lead to poor recovery of TNb or DNb. Suspected problems can be identified by determining nitrogen before and after suitable dilution, or by using standard addition techniques.
Not all organic nitrogen compounds are quantitatively converted to nitrogen oxide by the combustion procedure described, and consequently to nitrogen dioxide by the reaction with ozone. Poor recoveries can occur with compounds containing either double- or triple-bonded nitrogen atoms. The use of a calibration function calculated in accordance with 10.2 and applying a nitrogen mixed standard solution II (6.9.3.4) can result in a negative TNb bias for ammonium-N determinations (e.g. ammonium sulfate solution) and a positive bias for nitrate-N determinations (e.g. potassium nitrate solution).BS ISO 20236 pdf free download.
