BTEX in ambient air.
BTEX in ambient air.
Atmospheric VOC monitoring is crucial for understanding, tracking and implementing controls on sources of anthropogenic VOC emissions. VOCs are monitored around the world for their direct health effects, contribution to photochemical smog and environmental damage.
A commonly measured group of anthropogenic compounds is BTEX (Benzene, Toluene, Ethyl Benzene and Xylenes), which is often measured to provide a good marker for the total VOC concentration in urban and polluted environments1. BTEX is most commonly found in the solvent and petrochemical industry, providing the high-octane components of gasoline mixtures2.
As a result of their prevalence in industry, BTEX is often found in the atmosphere and is measured extensively in urban and industrial environments by researchers and governmental bodies.
To determine BTEX VOC concentrations in urban and industrial environments, a method for rapid, real-time quantitative measurements in the ppbv range is required. The Kore Technology PTR 3c with AnalyseHR is well suited to this analysis with sub ppbv detection limits and efficient ionisation by protonation and charge exchange of all the target compounds.
The 4 individual compounds in BTEX were measured using a gas standards generator to determine the sensitivity, limits of detection (LOD) and product ion distributions for each of the compounds.
Table 1: Sensitivity and limit of detection for BTEX for the Kore Technology PTR 3c (sensitivity derived from measurements of benzene gas standard)
|Compound||Sensitivity (cps/ppbv)||Limit of detection (ppt, 3σ)|
The PTR 3c has a high sensitivity and low limit of detection for all the target compounds in BTEX analysis.
We also used our high-resolution fitting software, AnalyseHR to deconvolute the mass spectra of a mixture of the BTEX compounds in simulated air samples, producing accurate VOC concentrations in a single click. The data for several mixtures were run through the AnalyseHR software to produce on-line real time concentrations.
With AnalyseHR we utilise mixed mode ionisation (Protonation and Charge exchange) in order to give greater discriminating power for mixtures of isotopes and interfering compounds. As the composition of oxygen in air and the reagent ion flows are fixed and stable, the mixed mode ionisation for AnalyseHR gives us repeatable and reliable deconvolution results.
This approach is unique to Kore Technology PTR-MS instruments.
Analysis of several different mixtures of BTEX shows accurate reporting of individual components of the BTEX mixture in air.
Table 2 – AnalyseHR determination of compound concentrations in two simulated air BTEX mixtures (40% RH zero air with BTEX from Air Products gas standard). Data analysis time (experiment length) was 10 seconds for each mixture, with the calculation taking <1 second.
|Compound||Mix 1 Concentration (ppb)||Mix 1 Reported Concentration (ppb)||Mix 2 Concentration (ppb)||Mix 2 Reported Concentration (ppb)|
* Low concentrations of Benzene, Toluene, Ethylbenzene and Xylene are present in the zero air used in this experiment. This was confirmed by a secondary method at 1-1.5ppb per component.
AnalyseHR can be used for on-line analysis, plotting real time VOC concentration for VOC targets. The PTR 3c with Analyse HR is an ideal tool for quantification and deconvolution of targeted mixtures of BTEX and other VOCs.
Kore Technology is a centre of excellence in time-of-flight mass spectrometer technology and has a very strong R&D capability in terms of its personnel, all of whom have been heavily involved in a variety of analytical instrumentation development programmes.