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HJ 644-2013: Ambient air. Determination of volatile organic compounds. Sorbent adsorption and thermal desorption/gas chromatography mass spectrometry method
HJ 644-2013
HJ
ENVIRONMENTAL PROTECTION STANDARD
OF THE PEOPLE’S 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 μg/m3; the lower limit of determination is 1.2~4.0 μg/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 μm 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 μL.
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 μL 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 ...