5. Analysis steps

5.1 Chromatographic analysis conditions

Because chromatographic analysis conditions often vary with different experimental conditions, the best chromatographic analysis conditions for the analysis of carbon monoxide should be established according to the model and performance of the gas chromatograph used. An example of a chromatographic analysis condition is listed in the appendix.

5.2 Draw the standard curve and measure the correction factor Draw the standard curve or measure the correction factor under the same conditions as the sample analysis.

5.2.1 Preparation of standard gas

In 5 100ml syringes, dilute standard carbon monoxide gas of known concentration with pure air to 4 concentration points in the range of 0.4 ~ 40ppm(0.5 ~ 50mg/m3). In addition, pure air is taken as the zero concentration gas.

5.2.2 Draw standard curve

Each concentration of standard gas was injected through the six-way injection valve of the chromatograph, and 1ml of the sample was measured to obtain the chromatographic peak and retention time of each concentration. Each concentration is repeated three times to measure the mean peak height. The peak height (mm) was used as the coordinate, and the concentration (PPM) was used as the coordinate to draw the standard curve, and the slope of central regression was calculated. The slope reciprocal Bg (PPM /mm) was used as the calculation factor of sample determination.

5.2.3 Determination of correction factor

Calibration factor was obtained by single point correction method. A standard gas with a concentration close to that of carbon monoxide in the air of the sample is taken. The mean peak height (cm) and retention time of chromatographic peaks were measured according to 6.2.2. Calibration factor (f) is calculated by formula (1) :

F = h0 / C0..................................................................... (1)

Where: F -- correction factor, PPM /mm

C0 -- standard gas concentration, PPM

H0 -- Average peak height, mm

5.3 Sample analysis

Through the six-way sample inlet valve of the chromatograph, 1ml of sample air was injected. Operation was carried out according to 6.2.2 to qualitatively measure the peak height of carbon monoxide with retention time. Three analyses were made for each sample and the average peak height was obtained. Temperature and atmospheric pressure at the time of analysis were recorded. High concentration samples were diluted to less than 40ppm (50mg/m3) with clean air and then analyzed.

CO

6. Calculation of results

6.1 The standard curve method is used to check the standard curve for quantitative analysis. Formula (2) may be used to calculate the carbon monoxide concentration in the air.

C = h x Bg.................................................................................... (2)

Where: C -- carbon monoxide concentration in the air of the sample, PPM.

H -- the average peak height of the sample, mm Bg -- the calculation factor derived from 6.2.2, PPM /mm.

6.2 Use correction factor to calculate concentration according to Equation (3) :

C = h x f............................................................... (3)

Where: C -- carbon monoxide concentration in the air of the sample, PPM;

H -- average peak height of the sample, mm;

F -- correction factor obtained from item 6.2.3, PPM /mm;

6.3 The volume concentration of carbon monoxide PPM can be converted to the mass concentration mg/m3 in standard state according to Equation (4);

Mg/m3 = PPM/B * 28.......................................................................................... (4)

7. Measuring range, precision and accuracy

7.1 Determination range When 1ml was injected, the concentration range was 0.50-50.0 mg/m3

7.2 The minimum detection concentration was 0.50mg/m3 when the lower limit of injection was 1 mL.

Because of the gas chromatography separation technology, air, methane, carbon dioxide and other organic matter do not interfere with the determination.

7.4 Reproducibility: When the CO concentration was 6mg/m3, the coefficient of variation was 2% for 10 injection analyses.

The recovery rate was 94-104% when the concentration of CO was in the range of 3-25 mg/m3.

Test method for carbon monoxide in air (1)

Test method for carbon monoxide in air (2)

Test method for carbon monoxide in air (3)