Chromatography issue, seeking advice!
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When using a gas cylinder to introduce samples, the nitrogen level in the analyzed data can sometimes be high; repeating the analysis a few times fixes it. What the hell?
Hydrogen recovery method, coco2n2ch4
The effect of nitrogen in the air is the main factor. Because there was air residue in the injection tube at the initial injections, as the number of injections increased, the proportion of air residue decreased, and the measurement results of the sample approached the actual values. During sampling, the sampling tube or sampler should be thoroughly filled with the sample, which helps to reduce the impact of air; this effect can be accounted for by deducting the proportion of air (nitrogen + oxygen) from the analysis results.
Pipeline flushing before sampling can be increased. It depends on the length of your injection line and the structure of that line. If it is just a straight pipeline, the effect can be achieved with a long replacement time; but if it is not a straight pipeline, sampling for replacement is still necessary, and this is your current situation.
Precautions for gas calibration standards: 1. Thoroughly purge the gas lines before sampling to ensure that there is no gas present in the entire sampling pipeline (quantitation loop, gas connection points)
Precautions for gas calibration standards: 1. Thoroughly purge the gas lines before sampling to ensure that there is no gas present in the entire sampling pipeline (quantitation loop, gas connection points)
Precautions for gas standards: 1. Thoroughly purge the gas lines before sampling to ensure that there is no gas present in the entire sampling pipeline (including the quantitation loop and gas connection points). 2. Ensure that the standard gas is well mixed before sampling, so that it is homogeneous and representative; shake it horizontally for at least 5 minutes each time it is sampled, as gas molecules have different molecular weights and thus diffuse unevenly. 3. Make sure that there are no leaks in the instrument’s six-way or ten-way valves
Additional note: It is necessary to ensure consistency in the gas flow rate for each injection (the bubbles should escape one by one; otherwise, variations in the volume injected with each sample will occur, just as required by the external standard method regarding the injection volume)
It’s mainly due to residual air; just wash it several times with sample gas.