Basic knowledge of gas chromatography quantitative analysis
How is the gas chromatograph quantified? Of course, it is quantified by peak area or peak height. So why can you quantify peak area or peak height? We know that chromatographic analysis is done in any case, and the results are very accurate. During my studies, my teacher answered me this question when I asked questions. Natural Plant Pigment,Plant Pigments,Natural Pigments,Plant Based Pigments Shaanxi Zhongyi Kangjian Biotechnology Co.,Ltd , https://www.zhongyibiology.com
In fact, chromatography can be so quantitative, there are two important reasons.
The first one is the linear response of the detector. I talked about this in our lecture on FID in Lu Chuang. In all chromatographic detectors, all detectors except FPD follow a linear response, that is, m = KS. Here, m refers to the amount of the substance to be tested (including the mass or the amount of matter) reaching the detector per unit time, K represents the linear response coefficient, and S represents the value of the detector response signal. That is to say, the size of the gas chromatograph detector response signal is proportional to the total amount of the test substance reaching the detector per unit time. Of course, we also know that this relationship is scoped, too large or too small, and will be out of line.
The second is the tray theory. The tray theory fully illustrates the relationship between peak height and injection volume, or directly proportional to them. This can refer to my explanation of the tray theory.
According to these two articles, it can be said with certainty that the peak height of the substance to be tested is proportional to the total amount of the sample to be tested. Or using calculus, it can be inferred that the peak area of ​​the substance to be tested is proportional to the total amount of the sample to be tested. Since the peak height and peak area are directly proportional to the total amount of injection, why do we prefer to use the peak area instead of the simpler peak height? This problem is also very simple, because the tray theory is not completely correct, and the peak shape often does not completely satisfy the normal distribution, so the peak height is not representative enough. When can the peak height be well represented? It is obvious that the peak shape is good and symmetrical, when it is in the shape of a good normal distribution curve. Or, when the peak shape is sharp and symmetrical. The peaks are often tailed, so what do we do? It is very simple, it can be quantified by peak area, and the peak area is very representative in most cases. Then, when the peak area is also underrepresented? Yes, when the gas chromatograph detector is overloaded, or the analog-to-digital converter is overloaded, or the peak area is not accurately integrated, or when the injection is underrepresented, and in some other special cases, the peak area cannot be used to obtain the correct result. But in any case, quantification of peak area is already the most accurate method we can, so we have almost no choice.