* Question
| What is the internal standard method? How to choose the internal standard? |
* Answer
| accuracy of the analysis result.The internal standard method is an important technique in the quantitative analysis of gas chromatography.The choice of internal standard is a very important task when quantifying by internal standard method.It should have substantially the same or as close as possible the physicochemical properties (such as chemical structure, polarity, volatility, solubility in solvent, etc.), chromatographic behavior and response characteristics of the sample components being analyzed, preferably analyzed.a homologue of matter.It should be pointed out that in a few cases, the analyst may be more concerned about the recovery rate of the compound in a complicated process. At this time, he can use a chemical plant that is easily recovered completely in the process.The internal standard is used to determine the percent recovery of the compound of interest,Changes in the area ratio resulting from chemical reasons often occur when analyzing repeated samples.The chemical factors include:
1. The internal standard is not well mixed in the sample; 2. The reaction between the internal standard and the sample component occurs, 3. The purity of the internal standard is variable.Then there must be some important chromatographic problems, such as the injection volume change is too large, there is a big difference between the sample component concentration and the internal standard concentration, the detector nonlinearity.The injection volume should be small enough and remain constant so as not to saturate the detector and the integration device.The most powerful evidence for doubt about the integration device is that the area ratio is variable and the peak-to-height ratio remains relatively constant. What should you pay attention to when making the internal standard curve? When using the internal standard method for quantitative analysis of color, first prepare a certainChromatographic analysis of the mixture of the measured component and the internal standard sample in the weight ratio, measuring the peak area,The chromatographic conditions used in the actual sample analysis should be as close as possible to the conditions used in the preparation of the standard curve. Therefore, when preparing the standard curve, not only the chromatographic conditions (such as stationary phase, column temperature, carrier gas flow rate, etc.) should be indicated.The injection volume and internal standard concentration should also be indicated.If the curve changes during the hinge period, it should not be quantified using the internal standard method. |
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