Mass Spectrometry & Spectroscopy
Measurement of VOCs in Vehicle Interiors Using Thermal Desorption GC-MS with Nitrogen as the Carrier Gas
Waldemar Weber, Shimadzu Europa GmbH
The amount of toxic volatile organic compounds (VOC) in the air is one index of the extent of air pollution and is used for environmental monitoring in factories, urban areas, and indoor environments. VOCs can be measured effi ciently using TD-GC/MS, which does not require solvent extraction.
Helium is the most frequently used carrier gas in GCMS analysis. Due to its inertness it allows high sensitivity analysis combined with very good chromatographic separation. As the worldwide production of Helium is decreasing while the demand is permanently growing, Helium prices have doubled in the last 12 months. As the gap between supply and demand is expected to persist for longer times, further price increases are likely.
In this article, analysis was performed using nitrogen rather than helium as the carrier gas. Nitrogen gas can be less sensitive than helium gas, but it is inexpensive and readily available.
An analysis was performed of VOCs typically analysed in voluntary assessments of vehicle interiors and vehicle interior materials, using thermal desorption GC/MS with nitrogen as the carrier gas. The calibration curve, repeatability and effi ciency of retrapping were also tested.
Analysis System
In the TD-30R thermal desorption instrument, the sample gas collected within a sample tube is thermally desorbed and then concentrated in a cold trap before injection into the GC-MS. In theTD-30R, there is a retrapping function that collects the split sample gas again in a tube, and a function that automatically adds the internal standard. Using this retrapping function reduces the risk of analysis failure. In addition, the value calculated by the retrapping function can be corrected by using this function together with the internal standard auto addition.
Table 1. Analytical Conditions. Analytical Conditions Model Autosampler
Tube Desorption Temperature Tube Desorption Flow
Trap Cooling Temperature Trap Desorption Temperature Valve Temperature
Transfer Line Temperature
Injection Mode Split Ratio Carrier Gas
Carrier Gas Control Column
Figure 1. TD-30R + GCMS-QP2020 NX. Column Temp Measurement
The standard mixture of toluene, benzene, ethylbenzene, m,p,o-xylene, styrene, 1,4-dichlorobenzene, and tetradecane diluted with methanol were prepared with concentrations of 10ppm, 40ppm, 100ppm, 400ppm, and 1000 ppm. These standard mixtures were added 1µL to each TENAX-TA sample tube and then analysed. The analytical conditions are shown in Table 1. During the analysis, toluene-d8 was added by theTD-30R’s internal standard automatic addition function.
Ion Source Temperature Interface Temperature Acquisition Mode Event Time m/z Range
GCMS-QP 2020 NX TD-30R
[TD-30R]
280°C (10 min) 60 mL/min -20°C
280°C (10 min) 250°C 250°C
[GC]
Split 1:50
Nitrogen Linear Velocity (40 cm/sec)
SH-5MS (P/N 221-758555-30), Shimadzu (30 m ×0.25 mm I.D., 0.25 µm)
40 °C(1 min) with 10 °C/min to 100 °C, 40 °C/min to 200 °C, 20 °C/min to 300 °C (5 min)
[MS]
230°C 280°C SCAN
0.3 sec m/z = 45-600
INTERNATIONAL LABMATE - JULY 2022
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