BTEX on the Lucidity GC-FID
Volatile organic compounds, or VOCs, is a term given to organic compounds that become a gas at ambient temperatures and pressures. These VOCs are monitored because many are hazardous to human health, with several being a carcinogen. The source of these VOCs are industrial processes, vehicle emissions, and even natural sources such as forest fires.
The most commonly monitored group of VOCs is BTEX. This group has gotten more popular with VOCs analysis and provide a snapshot of VOCs that may be found in most urban environments.
What is BTEX? Well, BTEX is made of Benzene, Toluene, Ethylbenzene, and Xylenes (comprised of three isomers of dimethyl benzene). Why do we care about BTEX? Each of these solvents are used in a variety of ways in industrial applications, and can be introduced to the environment where they can cause many problems.
Benzene is used in unleaded fuel, which allows for a smoother running engine, the WHO has not set a safe exposure limit, stating that there is no safe level of exposure. Toluene, also known as methylbenzene, is used in a wide swath of industrial applications, with a global market of over 29 billion US dollars, and only expected to grow as more uses are found. Some common household uses are in glues and resins. Ethylbenzene is used in the production of styrene, which is then used in polystyrene, more commonly known as its trade name Styrofoam™. Last, xylenes are used in the production of plastic bottles and polyester fabrics, it is also used in the cleaning of circuit boards. With so many uses for each of these solvents, its easy to see how they are common in urban and industrial areas.
With urban and industrial areas having many VOCs present, why only measure only BTEX? With so many present, the analysis would get complicated and messy, taking excessive amounts of time to do the sample preparation and analysis. It becomes easier to be selective with which VOCs to analyze for and use these results as a marker for all VOCs that may be present in the area. These measurements could be used to tell how an industrial zone impacts the neighboring lands, or a company’s employees exposure to BTEX in a day, or even if there is a leak in storage containers, as well as compliance with local regulations.
How should BTEX be measured? The easiest way to measure BTEX is with a GC-FID. I have outlined the procedure I used to run BTEX below.
| Lucidity GC-FID Conditions | |||
|---|---|---|---|
| Carrier | Hydrogen | ||
| Control | Pressure | ||
| Flow | 2.0 mL/min | ||
| Split ratio | 25:1 | ||
| Column | Rtx-624 | 30 m x 0.25 mm, 1.4 μm | |
| Injector | 300 ℃ | ||
| FID | 325 ℃ | ||
| Oven Program | |||
| Rate | Temperature | Hold Time | |
| 40 ℃ | 4.0 min | ||
| 4 ℃/min | 160 ℃ | 5.0 min | |
I used the BTEX standard from Restek (p/n 30488) and made a calibration curve of 2000, 200 and 100 μg/mL. The calibration curve was run using the method outlined above and the results were good.
Chromatogram of the 2000 ug/mL BTEX
Each of the expected peaks was well resolved, except for the m-Xylene and p-Xylene, which is to be expected. Peak shape was excellent and the software was able to integrate each peak easily. These runs were then input into the calibration curves for each compound, which are shown below.
Calibration curve of Benzene
m-, and p-Xylene calibration curve
o-Xylene calibration curve
Toluene calibration curve
The curve is great and really shows the range of the linearity of the different compounds in the BTEX mixture. Each had an R squared value in the range from 1 to 0.9994 for ethylbenzene at the lowest, so this method demonstrates an easy way to run BTEX samples and get reliable results via GC-FID.