GB/T 9722-2023Chemical reagent—General rules for the gas chromatography (English PDF)

3.1 Asymmetric factor

A parameter that describes the degree of asymmetry of a chromatographic peak.

3.2 Height of an effective plate

The length of unit effective plate.

5.1 Standard Sample

The mass fraction of the main body content of the standard sample shall not be lower than 99.9%. When high-purity standard samples cannot be obtained for special substances, standard samples with clarified main body content shall be used.

5.2 Reference Substance

The reference substance shall be traceable to International System of Units (SI) or certified reference substance.

5.3 Carrier Gas

The purity is not lower than 99.99%. Before use, dehydration devices (silica gel and molecular sieve), activated carbon and deoxidizer, etc. shall be used for purification.

5.4 Combustion Gas

The purity is not lower than 99.99%. Before use, dehydration devices (silica gel and molecular sieve), activated carbon and deoxidizer, etc. shall be used for purification.

5.5 Air

It does not contain dust, hydrocarbons, moisture and corrosive substances that may affect the normal operation of the instrument. Before use, dehydration devices (silica gel and molecular sieve) and activated carbon, etc. shall be used for purification.

6.1 Composition of Gas Chromatograph

The gas chromatograph consists of gas path system, sample injection system, separation system, detection system, temperature control system and data processing system, as shown in Figure 1.

6.2 Performance of Gas Chromatograph

The performance requirements for the gas chromatograph shall comply with the requirements of JJG 700.

6.3 Chromatographic Columns

The chromatographic columns are divided into capillary columns and packed columns. The important parameters of chromatographic columns are stationary phase, inner diameter, column length and liquid film thickness. The users shall select appropriate chromatographic columns based on sample properties. See Appendix A for the parameters of capillary chromatographic columns and the preparation and handling of packed columns.

8.1 Peak Height Measurement

Draw a vertical line from the top of the peak to the bottom of the peak. The distance from the point where the vertical line intersects with the upper edge of the chromatographic peak baseline to the top is the peak height (h). Or calculate the difference between the signal value at the peak apex and the baseline signal value at the same retention time as the peak apex (see Figure 2).

8.2 Measurement of Peak Width at Half Height

Draw a straight line parallel to the peak bottom from the midpoint of the peak height and intersect with both sides of the peak. The distance between two points on the same side of the peak height line is the peak width at half height (Wh/2) (see Figure 2).

8.3 Calculation of Peak Area

Calculate the integrated value of the difference between the signal value and the baseline signal value from the start of the peak to the end of the peak; or the product of the peak height and the peak width at half height.

8.4 Overlapping Peak Area Segmentation Method

8.4.1 Vertical method

As shown in Figure 3, when the areas of two peaks are similar, draw a vertical line from the peak valley toward the baseline to divide the peak on the baseline into two parts, so as to obtain the respective peak areas.

8.4.2 Peak-valley - peak-valley method

As shown in Figure 4, in accordance with the adjacent peak valley and peak valley linear distribution, obtain the corresponding peak area. This method is applicable to background overlapping peaks.

8.4.3 Tangent method

As shown in Figure 4, when a small peak overlaps the tail of a large peak, draw a tangent line from the peak valley to the foot of the large peak, and use the part above the tangent line as the area of the small peak. The exponential function curve method can also be used instead of the tangent method for peak segmentation.

9.1 Comparative Qualitative Analysis of Known Substance

9.1.1 Adding known substance to increase peak height

Under the same chromatographic conditions, add a known substance to the sample to be tested, and compare the changes in the chromatographic peak height of the sample to be tested before and after the addition. If the peak of the component to be determined in the sample to be tested increases, it can be considered that the component and the known substance are the same substance.

9.1.2 Qualitative analysis with double-column or multi-column

On two or more chromatographic columns of different polarities, respectively analyze the known substance and the sample to be tested under the same chromatographic conditions. If the retention values of the known substance and unknown component in the sample to be tested are the same on different chromatographic columns, the component and the known substance can be considered to be the same substance.

9.2 Qualitative Analysis of Relative Retention Value

9.2.1 Under the same chromatographic conditions, respectively perform chromatographic analysis on the standard sample and the sample to be tested and calculate the relative retention Baseline

9.2.2 If the standard sample cannot be obtained, the relative retention value of the known substance can be obtained by searching the literature, then, under the test conditions (column temperature, stationary phase and reference substance) provided by the literature value, determine the relative retention value of the sample to be tested; if it is consistent with the literature value, it can be identified as the same substance.

10.1 Correction Factor

10.1.1 General requirements

This document adopts a mass correction factor for component i relative to the main body.

For individual components listed in technical indicators, the mass correction factor will be used regardless of the mass fraction. Among the components to be determined, for homologues with relatively close carbon numbers or substances with small thermal conductivity differences, a correction factor may be added depending on the specific situation.

10.2 Normalization Method

When adopting the normalization method for quantitative analysis, the following requirements shall be satisfied.

10.4 External Standard Method

10.4.1 General requirements

When adopting the external standard method for quantitative analysis, the following requirements shall be satisfied.

10.4.2 Single-point external standard method

Prepare a standard solution with a mass fraction close to that of the component to be determined.

In accordance with the same determination conditions, respectively determine the standard solution and the sample to be tested. Through the peak area ratio of the component to be determined and the external standard component, calculate the mass fraction of the component to be determined.

10.4.3 Standard curve method

Prepare no less than 5 standard solutions with proportional mass fractions and quantitatively inject the sample. Take the mass fraction of the component to be determined as the x-coordinate and the measured peak area as the y-coordinate to draw a standard working curve. Under the same determination conditions, inject the same amount of the sample to be tested for chromatographic analysis, determine the peak area of the sample, and in accordance with the standard working curve, calculate the mass fraction of the component to be determined (see Figure 6).

10.6 Result Expression

10.6.1 The arithmetic mean of two repeated determination results shall be used as the test result, which shall be rounded in accordance with the stipulations of GB/T 8170.

10.6.2 When the mass fraction of the component to be tested is not less than 1%, the test result shall be accurate to 0.01% (mass fraction).

10.6.3 When the mass fraction of the component to be tested is not less than 0.01% and less than 1%, the test result shall be accurate to 0.001% (mass fraction). […]