Analysis issues of hydrogen sulfide
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Ladies and gentlemen: When analyzing hydrogen sulfide using a FPD detector in gas chromatography, the final results obtained for the same sample after dilution by a factor of 2 and by a factor of 5 differ significantly; the result obtained after a 2-fold dilution is 1000 Ppm, while that after a 5-fold dilution is 1500 Ppm. The standard gas used contains 400 Ppm of hydrogen sulfide – why is there such a large discrepancy? I seek the guidance of experts.
Why is there such a large deviation?
First, let’s talk about the dilution issue: can it be confirmed that there are no problems during the dilution process? If the instrument’s measurements are correct, the problem lies most likely in the dilution process. Additionally, in cases of such large errors, you can use other methods for verification, such as measurement with an H2S detector tube. If possible, you can also try chromatography for the determination of constant sulfur; at a concentration of around 1000 PPM, that is, 0.01%, detection of this constant sulfur should be possible. If the above conditions are not met, the original poster can use your 400 ppm standard gas for dilution and verification testing. Regarding the instrument issue, it’s impossible to determine the cause since it’s unclear what configuration the original poster is using
Chromatographic determination of organic sulfides and hydrogen sulfide using an FPD detector is a mature and reliable method.
Chromatographic determination of organic sulfides and hydrogen sulfide using an FPD detector is a mature and reliable method. Regarding the situation described by the original poster, I believe the reasons should be sought in the following aspects: 1. The reliability of the standard samples and the calibration of the instruments; 2. The accuracy of sample dilution, especially whether the method used for diluting gas samples is reliable; 3. What type of gas is used for dilution – this is very important; if air is used for dilution, it’s normal for the resulting data to be unreliable. In my opinion, the emergence of such analysis results is entirely due to the operator’s lack of understanding of the sample properties, as well as the use of incorrect gas dilution methods and diluent gases.
This post was last edited by qugd on 2017-8-11 09:53. If the sulfur content of the sample exceeds the detection range of the chromatograph, it is possible to try diluting the sample with nitrogen or hydrogen, which will make the analysis results more reliable. Hydrogen sulfide is a strong reducing agent; when diluted with air, the oxygen in the air will oxidize hydrogen sulfide, resulting in significantly low values. The greater the dilution ratio, the larger the deviation. When making judgment and analysis, it is necessary to consider all relevant factors, including the properties of the components and the environmental conditions involved.
H2S has extremely strong adsorption properties, so the sampling lines generally also need to be passivated; moreover, errors are inevitable when diluting