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HJ 644-2013 English PDF (HJ644-2013)

HJ 644-2013 English PDF (HJ644-2013)

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HJ 644-2013: Ambient air. Determination of volatile organic compounds. Sorbent adsorption and thermal desorption/gas chromatography mass spectrometry method

This Standard specifies the sorbent adsorption and thermal desorption / gas chromatography mass spectrometry method for the determination of volatile organic compounds (VOCs) in ambient air. This Standard applies to the determination of 35 volatile organic compounds in ambient air. If verified, this Standard can also be applied to the determination of other non-polar or weakly polar volatile organic compounds.
HJ 644-2013
HJ
ENVIRONMENTAL PROTECTION STANDARD
OF THE PEOPLE REPUBLIC OF CHINA
Ambient air - Determination of volatile organic
compounds - Sorbent adsorption and thermal
desorption / gas chromatography mass spectrometry
method
ISSUED ON: FEBRUARY 17, 2013
IMPLEMENTED ON: JULY 01, 2013
Issued by: Ministry of Environmental Protection
Table of Contents
Foreword ... 4
1 Scope of application ... 5
2 Normative references ... 5
3 Method principle ... 5
4 Reagents and materials ... 6
5 Instruments and equipment... 6
6 Sample ... 8
7 Analytical procedures ... 9
8 Calculation and expression of results ... 13
9 Precision and accuracy ... 14
10 Quality assurance and quality control ... 15
11 Matters needing attention ... 15
Appendix A (Normative) Detection limit and lower determination limit of target ... 16
Appendix B (Informative) Reference information for target determination ... 17 Appendix C (Informative) Precision and accuracy ... 18
Ambient air - Determination of volatile organic
compounds - Sorbent adsorption and thermal
desorption / gas chromatography mass spectrometry
method
Warning: The standard solution used in the test is a volatile toxic
chemical. The solution preparation process shall be operated in a fume
hood. The operator shall wear protective equipment.
1 Scope of application
This Standard specifies the sorbent adsorption and thermal desorption / gas chromatography mass spectrometry method for the determination of volatile organic compounds (VOCs) in ambient air.
This Standard applies to the determination of 35 volatile organic compounds in ambient air. If verified, this Standard can also be applied to the determination of other non-polar or weakly polar volatile organic compounds.
When the sampling volume is 2 L, the detection limit of the method of this Standard is 0.3~1.0 ??g/m3; the lower limit of determination is 1.2~4.0 ??g/m3. See Appendix A for details.
2 Normative references
The contents of this Standard refer to the following documents or their provisions. For the undated references, the valid edition applies to this Standard. HJ/T 194 Manual methods for ambient air quality monitoring
3 Method principle
USE a solid sorbent to enrich the volatile organic compounds in the ambient air; PLACE the adsorption tube in a thermal desorption apparatus; USE gas
chromatography to separate; USE mass spectrometry to detect. Compared with the standard mass spectrogram of the target to be determined and the retention time, carry out the qualitative analysis. USE the external standard method or internal standard method for quantitative analysis.
temperature.
Note 2: The gas chromatograph is equipped with a column oven cooling device, which can improve the peak type of the extremely volatile target and increase the sensitivity. 5.2 Mass spectrometer: Electron impact (EI) ionization source. It is capable of scanning from 35 amu to 270 amu in one second; has functions such as NIST mass spectrogram library, manual / automatic tuning, data acquisition,
quantitative analysis and spectral library search.
5.3 Capillary column: 30 m ?? 0.25 mm; 1.4 ??m in film thickness (6% nitrile propylbenzene, 94% dimethyl polysiloxane stationary liquid). Other equivalent capillary columns can also be used.
5.4 Thermal desorption device
The thermal desorption device shall have a secondary desorption function. The focusing tube part shall be able to heat up quickly (at least 40 ??C/sec). The part connecting the thermal desorption device to the gas chromatograph and the gas pipeline in the instrument shall use silanized stainless steel tubes. They can be heated uniformly at least between 50~150 ??C.
Note 3: The use of a thermal desorption device with cold focusing function can reduce the loss of extremely volatile targets and improve sensitivity.
5.5 Aging device
The maximum temperature of the aging device shall be above 400 ??C. The
maximum carrier gas flow can reach at least 100 ml/min. The flow can be adjusted.
5.6 Sampler
Dual-channel oil-free sampling pump. The dual-channel can independently adjust the flow rate and accurately maintain the flow rate within 10~500 ml/min. The flow rate error shall be within ??5%.
5.7 Calibration flowmeter: It can accurately measure the flow rate within 10~500 ml/min. The flow rate accuracy is 2%. Electronic mass flowmeters should be used.
5.8 Micro syringe: 5.0, 25.0, 50.0, 100, 250 and 500 ??L.
5.9 Commonly used instruments and equipment in laboratories.
least one on-site blank sample shall be taken for each sample collection. Note 4: Temperature and wind speed will affect sample collection. When sampling, the ambient temperature shall be less than 40 ??C. When the wind speed is greater than 5.6 m/s, during sampling, the adsorption tube shall be placed perpendicular to the wind direction; a bunker shall be placed upwind.
7 Analytical procedures
7.1 Reference conditions for instruments
7.1.1 Reference conditions for thermal desorption apparatus
Transmission line temperature: 130 ??C; initial temperature of adsorption tube: 35 ??C; initial temperature of focusing tube: 35 ??C; desorption temperature of adsorption tube: 325 ??C; desorption time of adsorption tube: 3 min; desorption temperature of focusing tube: 325 ??C; desorption time of focusing tube: 5 min; primary desorption flow rate: 40 ml/min; focusing tube aging temperature: 350 ??C; dry blowing flow rate: 40 ml/min; dry blowing time: 2 min.
7.1.2 Reference conditions for gas chromatograph
Inlet temperature: 200 ??C; carrier gas: helium; split ratio: 5:1; column flow (constant flow mode): 1.2 ml/min. Temperature programming: Initial
temperature is 30 ??C, kept for 3.2 min; the temperature is increased to 200 ??C at 11 ??C/min for 3 min.
Note 5: In order to eliminate the interference of moisture and the overload of the detector, the split ratio can be set according to the situation. Some thermal desorption apparatus have a sample split function, which can be set according to the manufacturer?€?s recommendations or specific conditions.
7.1.3 Reference conditions for mass spectrometry
Scan mode: full scan; scan range: 35~270 amu; ionization energy: 70 eV; interface temperature: 280 ??C. The remaining parameters are set according to the instrument manual.
Note 6: In order to improve sensitivity, selective ion scanning can also be used for analysis. Refer to Appendix B for characteristic ion selection.
7.2 Instrument performance check
USE a micro syringe to pipette 1.0 ??L of BFB solution (4.3) and directly inject it into the gas chromatograph for analysis. The abundance of BFB key ions
obtained by quadrupole mass spectrometry shall meet the standards specified adsorption tube shall be opposite to the direction the gas enters the adsorption tube during sampling. The target in the sample enters the chromatographic column with the desorption gas for determination. After the analysis is completed, remove the adsorption tube and age and store it according to step 4.7. If the sample concentration is low, the adsorption tube does not need to be aged.
7.4.2 Blank test
Analyze on-site blank sample in the same procedures as the sample
determination.
8 Calculation and expression of results
8.1 Qualitative analysis
Qualitative analysis is performed by comparing retention time and mass
spectrogram.
8.2 Quantitative analysis
Calculate according to the response value of the first characteristic ion of the target. When the first characteristic ion of the target in the sample has interference, the second characteristic ion can be used for quantification; see Appendix B for details.
8.2.1 Calculation of target mass in adsorption tube
8.2.1.1 External standard method
When using the least square method to draw the calibration curve, the target mass m (ng) in the sample is calculated by the corresponding calibration curve. 8.2.1.2 Internal standard method
When the average relative response factor is used for calibration, the mass m (ng) of the target in the sample is calculated according to formula (5). Where:
m - The mass of the target in the test portion, ng;
Ax - The response value of the quantitative ion of the target;
6 laboratories respectively measured the ambient air spiked samples with spiked amounts equivalent to 5.0 ??g/m3, 12.5 ??g/m3 and 35.0 ??g/m3. The spike recovery rates are: 56.4%~122%, 53.4%~126%, 76.1%~132%.
See Appendix C for the precision and accuracy results.
10 Quality assurance and quality control
10.1 Before collecting samples, 20% of the adsorption tubes shall be sampled for blank inspection. When the number of samples is less than 10, at least 2 shall be sampled. The concentration of the target in the blank tube equivalent to the sampling volume of 2 L shall be less than the detection limit, otherwise it shall be re-aged.
10.2 Before each sample analysis, it shall use a blank adsorption tube instead of the sample adsorption tube, to determine the system blank. The sample can be analyzed only after the system blank is less than the detection limit. 10.3 An intermediate concentration check point of the calibration curve shall be made every 12 h. The relative error between the measured value of the
intermediate concentration check point and the corresponding point
concentration of the calibration curve shall not exceed 30%.
10.4 The detection amount of a single target in the on-site blank sample shall be less than 10% of the corresponding detection amount in the sample or equivalent to the detection amount of the blank adsorption tube.
11 Matters needing attention
11.1 The residual VOCs in the adsorption tube interfere greatly with the determination. Strict implementation of the aging and storage procedures (4.7) can minimize this interference.
11.2 Newly-purchased adsorption tubes shall be marked with a unique code and an arrow indicating the direction of the sample air flow. An information card of the adsorption tube shall be established, to record information including the filling or purchase date of the adsorption tube, the maximum allowable use temperature and the number of times of use.

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