Gas chromatography is a fast and accurate method of quantification. To get accurate quantitative results, you must know the factors that affect the accuracy of chromatographic analysis. At present, the structure of modern chromatographs is more reasonable and advanced, and the wide application of computers has led to a reduction in various system errors. However, there is also a factor that is most negligible in the winery to influence the accuracy, namely the human factor.

1. Stability of the wine sample

The trace components of the wine are very complex and volatile, and are not well preserved. If it is not analyzed in time after sampling, the low-boiling volatiles will change in a short time, causing errors in the quantification and distorting the results.

2. Injection effect

Common injection methods for gas chromatography include manual injection and automatic injection. At present, the winery still uses manual injection. When manually injecting with a microinjector, the injection technique has an impact on the results of the analysis.

(1) Wash the micro syringe with the sample solution several times, slowly extract the microliter sample solution, you can see that there are small bubbles in the solution in the needle tube, put the micro syringe tip upwards, slowly push the piston to make the small bubble with the sample solution Drain and push to the desired injection volume.

(2) The injection speed should be rapid. Slow injection speeds can lengthen the vaporization process of the sample, causing the sample to enter the column to broaden the initial band. The shorter the time required to push the sample, the shorter the residence time of the syringe in the vaporization chamber should be, and the most important thing is that the needle retention time should be strictly controlled.

(3) The repeatability of the analysis depends on the size of the injection, the accuracy of the scale readings, and the position of the pins and the proficiency of the operator. For example, the ethyl acetate content in the wine sample is related to the injection amount and the technology. If the injection amount is large, the ethyl acetate peak and the ethanol peak are combined into one large peak, and the ethyl acetate cannot be quantified; if the injection amount is too small The ethyl acetate peak could not be separated and could not be quantified.

3. Avoid the effects between samples

(1) Wash the micro-injector more than three times with the sample solvent (sampling two-thirds of the needle tube before discharging), then wash the needle with the sample solution to be analyzed at least three times, then sample and twitch several times, then Basically eliminate mutual interference between samples.

(2) Before each wine sample, raise the column temperature (not to exceed the maximum temperature of the column) to remove the solvent and low molecular weight polymer remaining in the column from the previous sample, otherwise the effect will be The quantitative result of a sample.

4. The rubber pad of the vaporization chamber is easy to leak after the injection, which causes the baseline to drift, resulting in inaccurate quantitative results. Always check and replace, this is also the attention of the chromatographer.

5. Before preparing the standard sample, the purity of the reagent should be determined first, and the straws and volumetric flasks used for the preparation of the standard samples should be strictly corrected.

In summary, there are many human factors affecting the accuracy of chromatographic quantitative analysis, and the error of each step affects the total quantitative analysis accuracy. Therefore, only in the case of eliminating systematic errors, strict and careful operation can obtain accurate and accurate analysis results.