The paper presents the application of a method based on coupled gas chromatography-mass spectrometry, using an isotopically labelled internal standard for the quantitative analysis of benzene (B), toluene (T), ethyl benzene (E), and o-, m-, p-xylenes (X). Their atmospheric concentrations were determined based on short-term sampling, in different sites of Cluj-Napoca, a highly populated urban centre in N-W Romania, with numerous and diversified road vehicles with internal combustion engines. The method is relatively inexpensive and simple and shows good precision and linearity in the ranges of 7–60
Even when present at low concentrations compared to other air contaminants, due to their toxic properties VOCs are of concern as they pose risk for humans health [
Methods for determining atmospheric levels of VOCs use preconcentration from canister samples [
The aim of this study is to apply an SIM/GC-MS method for determining the levels of atmospheric BTEX concentrations. The methods high selectivity and specificity are due to the mass spectrometer operating in the selected ion monitoring mode SIM, which allowed the peak deconvolution of benzene and its perdeuterated analogue internal standard, as they were coeluting in the total ion chromatogram.
Homemade calibration solutions of the BTEX analytes (benzene, toluene, ethyl benzene, m-, p-, and o-xylene) were prepared, with concentrations ranging between 40 and 500 pL/mL, in dichloromethane DCM (Fluka, p. a.). The solvent, used in previous studies [
Preconcentration of the atmospheric contaminants was performed in SKC glass tubes filled with charcoal, using a portable, battery-operated pump set at 100 mL/min air flow, 45-minutes sampling time. A manually operated mechanical counter was used to determine the number of petrol-fueled vehicles passing the sampling site. The air samples were collected between 17
The analytes were separated using an Agilent GC 6890 gas chromatograph equipped with a capillary column DB-5 (30 m
The GC-MS response, averaged for duplicate injections, was calibrated using the ratio of the selected ions peak areas in each analyte to the perdeuterated benzene peak area at m/z 82 Da.
Figure
Example chromatogram of sample extract
The calibration equations and the method characteristics for each compound are shown in Table
Compounds analyzed and method characteristics: calibration equations and coefficients of correlation, linearity range, limits of quantization and of detection, precision, and accuracy RSD (
Compound | Equation | Linearity range ( | LOQ ( | LOD ( | Precision RSD (%) | Accuracy RSD (%) | |
---|---|---|---|---|---|---|---|
Benzene | 0.974 | 7–60 | 5 | 3 | 4.7 | 10.1 | |
Toluene | 0.964 | 13–90 | 3 | 1 | 11.2 | 9.7 | |
Ethylbenzene | 0.979 | 7–50 | 5 | 3 | 11.1 | 12.3 | |
m-, p-Xylenes | 0.946 | 10–70 | 5 | 3 | 13.0 | 11.6 | |
o-Xylene | 0.965 | 20–130 | 10 | 5 | 13.1 | 13.1 |
The method shows good precision (
Table
Values of the BTEX concentrations found in street air, during winter season, between: 17:00 and 20:00.
Crt. Nr. | Sampling site | B | T | E | m,p-X | o-X | T/B | ||
---|---|---|---|---|---|---|---|---|---|
1 | 25 | 21.4 | 71.9 | 22.7 | 61.4 | 39.6 | 3.4 | ||
2 | Horea street | 26 | 21.2 | 64.1 | 19.4 | 45.6 | 33.4 | 3.0 | |
3 | 15 | 22.2 | 62.2 | 18.6 | 50.0 | 35.2 | 2.8 | ||
4 | Limit | 8.8 | 53.9 | 8.5 | 15.8 | 27.4 | 6.1 | ||
5 | Central Park | 10 m inside | 19 | 7.8 | 42.72 | 8.2 | 12.1 | 26.6 | 5.4 |
6 | 50 m inside | 7.7 | 31.9 | 6.7 | 9.9 | 23.4 | 4.1 | ||
7 | 30 | 10.5 | 56.0 | 11.7 | 16.2 | 35.2 | 5.3 | ||
8 | Aurel Vlaicu street | 43 | 10.5 | 33.7 | 10.6 | 18.1 | 32.0 | 3.2 | |
9 | 33 | 11.0 | 18.6 | 8.2 | 12.9 | 25.8 | 1.6 |
Aurel Vlaicu street (samples #7–9) is a four-lane dual carriage way and represents the main access to the S-E exit of the town. It supports heavy trucks, and busy traffic, being the widest of the city boulevards. Despite a high average of 38 internal combustion vehicles per minute during sampling, the atmospheric concentrations of volatiles were smaller than those found on Horea street, due to the lower temperatures and light rain during sampling at site #7–9.
The concentrations of BTEX in the Central Park zone, samples #4–6, were the lowest, while the traffic along the park limit slightly decreased in time, between 17:00 and 20:00 sampling hours.
In sampling sites #1–3 and #7–9, both roads cross residential areas exposed to outdoor air polluted from road traffic. Among BTEX, toluene and xylenes (m,p) were found to be the major contributors to air contamination from engine exhausts gas. At sites 1–3 and 7–9, that is, on busy streets and street crossings, short-term sampling concentrations found for benzene in air exceeded 10
A chromatographic-mass spectrometric method was prepared and applied to assess atmospheric concentrations of BTEX in an urban centre of Romania, with a high density of vehicles with internal combustion. The GC-MS method has good precision and accuracy in the required dynamic range. In all the sites, the short-term sampling concentration of benzene in air may exceed the annual average value aimed as limit, while toluene and xylenes (m,p) are the most abundant of the BTEX air contaminants in the urban environment monitored.
The present work was supported by CNCSIS/Romania within the Grant no. 1258/2007-2008, and the analyses were performed in the Planetary and Space Sciences Research Institute, Milton Keynes, The Open University, UK.