Precautions for determination of non methane total

Precautions and quality assurance measures for the determination of non methane total hydrocarbons in the air by gas chromatograph

non methane total hydrocarbons refers to the general name of hydrocarbon compounds unexpected to methane, or the total amount of hydrocarbon compounds other than methane that have obvious response on the hydrogen flame ionization detector (FID) of gas chromatograph. It is expressed by the difference between the content of total hydrocarbons and methane in the air measured by FID, and its concentration value is calculated in carbon, with the unit of mg/m3

when the total hydrocarbon in air and exhaust gas is measured with nitrogen as the carrier gas, the peak of total hydrocarbon contains oxygen peak, that is, the oxygen in the gas produces positive interference. When the conditions of gas chromatography are certain, the response value of a certain amount of oxygen is certain. Therefore, the blank value can be obtained by removing hydrocarbons and purifying air, and the value can be deducted from the total hydrocarbon peak to eliminate the interference of oxygen

the precautions and quality assurance measures for the determination of non methane total hydrocarbons by gas chromatograph mainly include the following points:

1 environmental sample determination 5 when introducing to Zhao Wei, CEO of Argo, we should follow the sequence principle of "plant boundary samples before pollution source samples, and pollution source samples before export and import"

2 if there are multiple component peaks in total hydrocarbon analysis, the peak areas of all components should be added together as the response value of total hydrocarbon; The concentration of non methane total hydrocarbons in the gas is no longer subject to standard state conversion

3 when a real empty column is used for total hydrocarbon analysis, it will lead to difficult ignition of the gas chromatograph (FID) or easy flameout of the FID during the analysis process when using this tolerance table. The total hydrocarbon column properly filled with a small amount of glass beads or chromatographic supports will also have a certain separation efficiency. Therefore, when analyzing exhaust gas samples with complex components, the constant temperature time of the column should be kept long enough according to the actual situation of the sample, so that all components flow out, so as to prevent interference with the subsequent sample analysis. If necessary, a blank sample can be inserted for inspection

4 whether the oxygen content in standard gas and sample gas is consistent is one of the factors that affect the accuracy of this method and even after emergency relief personnel enter the cabin to remove injured passengers. When preparing methane and propane standard gas sample series with nitrogen as the base gas, high-purity nitrogen can be used as the diluent gas. When the high-concentration gas sample is diluted and analyzed by high-purity nitrogen, the hydrocarbon removal air with the same dilution ratio can be used as the blank value to be deducted; When preparing standard gas with air as the base gas or diluting the sample gas to be tested, purified air can be directly used

5 it should be ensured that the glass syringe used in the analysis has sufficient air tightness and can slide freely during gas extraction

6 the methane and propane standard gas samples prepared in the glass syringe lose quickly when placed, and the standard gas series samples should be prepared and used immediately

7 the nozzle and collecting electrode of gas chromatograph (FID) should be cleaned or replaced regularly according to the number of analysis samples