HJ 1223-2021Ambient air Emergency determination of volatile organic compounds - Portable gas chromatography-mass spectrometry (English PDF)

7.1 Sample Collection

7.1.1 The requirements for point layout and on-site monitoring shall be implemented in accordance with the relevant regulations of HJ 589.

7.1.2 Select an appropriate method according to the on-site situation, and use the gas sampling module of the portable gas chromatograph-mass spectrometer (5.3) for direct sampling;

When the field conditions are limited or the actual work requires, the vacuum gas sampling box (5.1) can also be used to collect air bag samples.

7.1.3 After sampling, air bag samples should be transported and stored in dark and normal temperature conditions, and should be analyzed as soon as possible.

7.2 Preparation of blank samples

Fill the pre-cleaned air bag (5.2) with nitrogen gas (4.4).

8.1 Instrument Reference Conditions

8.1.1 Adsorption thermal desorption reference conditions

Condition 1.Sampling probe temperature. 40 °C; heating line temperature. 70 °C; injection flow rate. 100 ml/min; adsorption tube desorption temperature.

300 °C; pre-desorption time of adsorption tube. 0.1 min; desorption time of adsorption tube. 0.5 min; splitless; injection volume. 5 ml to 100 ml.

Condition 2.Sampling probe temperature. 40 °C; heating line temperature. 70 °C; injection flow rate. 100 ml/min; adsorption tube desorption temperature.

300 °C; pre-desorption time of adsorption tube. 0.1 min; desorption time of adsorption tube. 0.5 min; split ratio of 50.1; injection volume. 6 ml to 600 ml.

Or set according to the instrument instruction manual.

8.1.2 Gas chromatography reference conditions

Condition 1.Column pressure. 80 kPa; splitless; temperature program. 60 °C for 3 min, 18 °C/min to 130 °C, and then 30 °C/min the temperature was raised to.200 °C and held for 1 min.

Condition 2.column flow rate. 0.2 ml/min; split ratio 50.1; temperature program. 60 °C for 1 min, 10 °C/min to 80 °C, and then Raised to 220 °C at 40 °C/min and held for 1 min.

Or set according to the instrument instruction manual.

8.1.3 Reference conditions for mass spectrometry

Ion source. EI; ionization energy. 70 eV; scanning mode. full scan; scanning range. 41 u~300 u. or use according to the instrument manual to set.

See Appendix C for the total ion chromatogram obtained from the determination of the target compound standard substance under the reference conditions.

Note. When the detection limit of the target compound does not meet the standard limit requirements, the ion scanning mode can be selected.

8.2 Calibration

8.2.1 Tuning

After starting up, firstly check the performance of the portable gas chromatograph-mass spectrometer (5.3) according to the instrument manual. to guarantee for the accuracy of the test results, after the startup, the mass spectrometer function should be tuned.

use request. Every 12 hours, the mass spectrometer function should be retuned. If the tuning substances are 1,3,5-tris(trifluoromethyl)benzene and bromopentafluorobenzene, then the abundance of key ions should meet the requirements of Table 1; if the tuning substance is perfluorotributylamine, the abundance of key ions should meet the requirements of Table 2, otherwise the parameters of the mass spectrometer should be adjusted; if other substances are used for tuning, the relevant requirements of the instrument manual should be met.

8.2.2 Plotting the calibration curve

8.2.2.1 Prefabricated calibration curve

In the laboratory, dilute the standard gas (4.1) with nitrogen gas (4.4) by means of a gas diluter (5.7), or use the static dilution method (see appendix).

Record B) Preparation of standard gas, prepared into low and high concentration series. Low concentration series are 2.0 nmol/mol, 5.0 nmol/mol, 10.0 nmol/mol, 25.0 nmol/mol, 50.0 nmol/mol (100 ml injection volume, splitless; or 600 ml injection volume, split ratio 50.1); high concentration series are 50.0 nmol/mol, 100 nmol/mol,.200 nmol/mol, 400 nmol/mol, 600 nmol/mol (in the sample volume is 5 ml, splitless; or the injection volume is 25 ml, the split ratio is 50.1), and the concentration series can be adjusted according to the actual sample conditions. According to the meter the instrument reference conditions (8.1) are measured sequentially from low concentration to high concentration, and the calibration curve is drawn and stored in the instrument. At the emergency monitoring site, If the calibration complies with the relevant requirements in 11.3, use a pre-made calibration curve for quantification.

8.2.2.2 Field calibration

At the emergency monitoring site, if the calibration does not meet the relevant requirements in 11.3, the site standard gas (4.2) should be used for single-point calibration.

At this time, the zero crossing should be forced.

Note. When 1,3,5-tris(trifluoromethyl)benzene and bromopentafluorobenzene (4.3) were used as internal standard compounds, the added amount of internal standard compounds was 20 µl, and 1,3,5-tris(4.3) was used as the internal standard compound. three when fluoromethyl)benzene and 4-bromofluorobenzene (4.3) were used as internal standard compounds, the added amount of internal standard compounds was 600 µl.

8.2.3 Average relative response factor method

The relative response factor (RRFi) of a target compound at point i in the standard series is calculated according to formula (1).

8.2.4 Calibration curve method

Taking the concentration of the target compound as the abscissa, taking the ratio of the quantitative ion response value of the target compound to the quantitative ion response value of the internal standard compound the product of the value and the concentration of the internal standard compound is the ordinate, and a calibration curve is established.

8.3 Sample concentration prediction

Before the sample measurement, the quick-check method, sample dilution or other methods specified in the instrument manual, combined with the on-site investigation situation, should be used to predict.

sample concentration.

8.4 Determination of samples

Collect the sample directly with the gas sampling module or connect the gas bag (5.2) to the gas sampling module, in accordance with the reference conditions of 8.1 and the sample in 8.3 According to the result of the pre-judgment of the concentration of the product, select the appropriate injection volume for the determination.

8.5 Blank test

Carry out the determination of the blank sample (7.2) according to the same conditions and steps as the sample determination.

9.1 Target compounds

9.1.1 Qualitative Analysis

By comparing the retention time, fragment ion mass-to-charge ratio and its abundance ratio of the target in the sample and the target in the standard series, the target the target is qualitative. The retention time of the target compound in the sample should be controlled within t±3S, where t is the target of each concentration level during the initial calibration.

The mean value of the retention time of the target compound, S is the standard deviation of the retention time of the target compound at each concentration level during the initial calibration. target compound all ions with relative abundance higher than 30% in the quasi-mass spectrum should be present in the sample mass spectrum, and qualitative judgment should be made in combination with the on-site situation. Such as If the actual sample has obvious background interference, the background influence should be deducted when comparing.

9.1.2 Quantitative analysis

Quantitative calculations were performed using the calibration curve method or the average relative response factor method. When the quantitative ion of the target compound in the sample interferes, Auxiliary ions can be used for quantification. See Appendix D for quantitative ions and auxiliary ions.

9.1.3 Result calculation

9.1.3.1 Average Relative Response Factor Method

When calculated by the average relative response factor method, the mass concentration 𝜌𝑥 of the target compound in the sample is calculated according to formula (3).

9.1.3.2 Calibration curve method

When the target compound is calibrated using a linear calibration curve, the mass concentration 𝜌𝑥 of the target compound in the sample is calculated according to formula (4).

9.2 Off-target compounds

9.2.1 Qualitative Analysis

Perform the determination in full scan mode, compare the mass spectrum of the sample with the mass spectrum of the standard material in the library, and the relative abundance in the mass spectrum of the standard material in the library all ions above 30% should be present in the sample mass spectrum, the signal-to-noise ratio of qualifier ions should be greater than 3.1, primary qualifier ions and secondary qualifiers the ion peak apex of the ion should be maximally co-elute in the same scan segment. According to information such as mass spectrum and spectral library matching degree, combined with the actual situation on site the qualitative results of the samples were obtained by judging the condition.

9.2.2 Concentration estimation

Integrate the chromatographic peaks of the total ion chromatogram of the qualitative target external compound and internal standard in the sample, and the mass of the target external compound is concentrated.

The degree rhox is estimated according to formula (5).

9.3 Result representation

The number of decimal places in the determination result is consistent with the detection limit of the method, and a maximum of 3 significant figures are reserved.

For non-target compounds, original information such as mass spectrum and search results should be attached to the qualitative results.

10.1 Precision

Actual samples spiked at 5.0 nmol/mol, 25.0 nmol/mol, 45.0 nmol/mol, and.200 nmol/mol by six laboratories the precision of the products was measured, and the relative standard deviations in the laboratory ranged from 2.2% to 25%, 1.1% to 24%, 0.6% to 14% and 1.0% to 1.0%.

13%; interlaboratory relative standard deviations were 4.1%-32%, 3.5%-20%, 2.9%-24%, 2.5%-28%; repeatability limit 3.3 µg/m3~20 µg/m3, 17 µg/m3~70 µg/m3, 19 µg/m3~1.3×102 µg/m3, 34 µg/m3~4.3×102 µg/m3;

The current limit is 4.7 µg/m3~36 µg/m3, 21 µg/m3~1.5×102 µg/m3, 26 µg/m3~1.4×102 µg/m3, 1.4×102 µg/m3~ 7.8×102 µg/m3.See Table E.1 in Appendix E.

10.2 Correctness

6 labs replicated 6 actual samples for samples spiked at 5.0 nmol/mol, 45.0 nmol/mol,.200 nmol/mol the recovery rate of standard addition was determined, and the recovery rate of standard addition ranged from 86.5% to 107%, 92.7% to 105%, and 94.3% to 106%;

The final values were 98.6%±36.2%, 100%±27.0%, 99.0%±33.0%, respectively. See Table E.2 in Appendix E.