What is the purity requirement for hydrogen used in FID gas chromatographs?
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For a FID gas chromatograph, with N2 as the carrier gas and H2 as the combustion gas, are there any requirements regarding the purity of hydrogen? Does the purity of hydrogen affect the test results or the instrument?
What scale of analysis are you doing? For the analysis of trace amounts of organic substances, the carrier gas, combustion gas, and auxiliary gases all need to be gases with low organic content, with a purity level of four nines or higher. Additionally, attention must be paid to removing organic substances from the purity of the carrier gas as well as from the air used for combustion.
For FID gas chromatographs, when hydrogen is used as the combustion gas, a high level of purity is required. Generally, the purity of hydrogen is required to be over 99.999%. This is because higher-purity hydrogen can reduce the interference of impurities on the flame ionization detector. The purity of hydrogen has an impact on both the detection results and the performance of the instrument. Hydrogen with lower purity may contain impurities such as water, oxygen, nitrogen, etc., and these impurities can interfere with the detection results or affect the stability and lifespan of the instrument. Therefore, ensuring high purity of hydrogen is one of the important factors in guaranteeing the proper operation of FID gas chromatographs and obtaining accurate results. .
The FID detector requires three types of gases; the carrier gas can be either N2 or H2. Unless the packed column uses H2 as the carrier gas, the FID only needs nitrogen and air to assist in combustion; if nitrogen is used as the carrier gas, sufficient H2 must be added. The trace organic substances present in hydrogen are mainly CH4 impurities, and combustion naturally results in a baseline level. For routine analysis, low purity is sufficient – 99.99% is adequate; however, for the analysis of trace organic substances, highly pure H2 is required, which must be purified using molecular sieves and activated carbon in order to reduce the detection limit and improve sensitivity.
Generally, 4 nines are required, but what we use in practice is 5 nines