First, the representativeness of sampling
Most of the products are low-to-medium wines. Due to the influence of the physicochemical properties of the components in the wine, many trace components in the wine will be distributed at different levels or interfaces. Therefore, the whole process from sample sampling to chromatographic analysis should be considered. After the uniform wine sample, if you do not pay attention to the sampling method, it will cause errors in the quantitative work.
Second, the accuracy of the quantitative response factor
In the actual quantitative work, the relative response factor is often introduced for calculation, and the accuracy of the quantitative response factor is directly related to the reliability of the analysis result. If the demand f value is valid, in principle, the content of the component is equivalent: on the one hand, the pure component to be tested is mixed with the pure standard to form a certain proportion of the mixed sample; on the other hand, the standard sample, the mixed standard, The f value of the monograph is the actual application of the f value, and if necessary, it can be verified by recycling the partial components before use.
Third, the cleaning of the outer wall of the syringe needle
For gas chromatograph capillary head injection, the material deposited on the wall during the injection process is transferred instantaneously under high temperature vaporization, which causes some deviation of the quantitative analysis results. Therefore, when analyzing different types of wine, Pay close attention to the cleaning of the outer wall of the syringe needle. The syringe needle can be immersed in a solvent to achieve effective cleaning, or it can be cleaned regularly.
Fourth, the impact of injection technology
The precision and accuracy of quantitative analysis depend on the repeatability of the injection and the technique of operation. For different sizes of capillary columns and special injection methods (on-column injection, split/splitless injection), the pin speed, position, depth and operator proficiency as well as the accuracy of the scale readings are certain. It is required that for large-diameter columns to stop the capillary column, the sample volume entering the column is very reproducible. For the medium-diameter, fine-diameter split/splitless injection capillary column, when the concentration range of the sample component is wide and the boiling point range is wide, shunt distortion is easy to occur, and the sample with low concentration and high boiling point has low recovery rate and precision. The degree is also poor. In summary, any method of injection cannot be adapted to all types of sample analysis, which requires chromatographers to optimize their selection in actual work.
Fifth, the life cycle of the silicone pad
The frequency of use of the silicone pad is generally compared by the number of injections. When the silicone pad is used for 15 to 20 times, it should be replaced in time. If the packed column used in the domestic gas chromatography instrument is used, the inner liner should be cleaned at the same time. Otherwise, the air leakage may cause the baseline to be stepped, peak-shaped, abnormal, etc., which affects the reliability of the analysis results.
Sixth, the size of the injection volume
The internal standard method for the quantitative quantification of liquor, although the size of the injection has no significant effect on the calculation results, but has a great influence on the currently used capillary column chromatography. First, the size of the injection directly affects the separation and characterization. Second, the size of the injection directly affects the change of the peak retention value, resulting in the partial retention of the peak retention time, thus affecting the quantitative results, especially for the workload. Large, large samples are more unsuitable, the impact on the large and small injection volume of ordinary packed column is not too large, but the injection volume will cause the peak to appear. For the capillary column, the injection mentioned here The amount is similar to the split ratio.
Seven, the standard calibration of the standard
In order to ensure the reliability of the test data, the mutual calibration between the gas chromatograph instruments and the calibration of the standard samples should be performed regularly to further understand the operation of the entire chromatographic system.
Eight, how to correctly evaluate the quantitative error
1. Unit consistency
The unit for quantitation of packed column chromatography is usually in mg/100ml, and the unit of gas chromatography capillary chromatography is expressed in mg/100ml, so the unit consistency should be considered while doing analysis and evaluation and evaluation error.
2, the consistency of content
Whether it is a standard sample or a chromatographically pure standard, the sample content at the f value (response factor value) is also consistent with the sample content in the daily analysis. It is well known that there are different error ranges for low content, the relative percentage error of high content is low, and the relative percentage error of low content is high. Therefore, the inconsistency or content difference between the contents is very different, which is easy to cause analysis. Some biases in error cannot correctly evaluate the error of the analysis results.