|Abstract Title:||Analytical system for direct real-time determination of benzene in air, natural gas, oil and its products by absorption spectrometry with the direct Zeeman effect|
|Session Choice:||Analytical Techniques|
|Presenter Name:||Dr Sergei Sholupov|
|Company/Organisation:||Lumex Analytics GmbH|
Abstract Information :
It is known that benzene has a strong absorption band (227.0 - 267.0 nm) with a partially resolved vibrational-rotational structure. Therefore, the method of differential absorption spectrometry with the direct Zeeman effect is applicable to the determination of benzene in any carrier-gas . Resonance mercury emission at a wavelength of 254 nm is used as a probing radiation. It is shown that the use of a lamp with the even mercury isotope makes it possible to achieve significantly higher sensitivity as with a lamp with the natural isotopic mixture. The method also completely eliminates interference of toluene on benzene determination. It is empirically demonstrated that, when benzene content is measured in the air at the Occupational Exposure Limit (OEL, 3.2 mg/m3 for benzene) level, the interference from SO2, NO2, O3 , H2S is negligible if concentration of these gases does not exceed corresponding OELs. To exclude the mercury effect, filters that absorb mercury and let benzene pass in the gas duct are proposed. Based on the results of our study, a portable analyzer is designed with a multipath cell of 960-cm equivalent path length and a detection limit of 0.5 mg/m3 per second on average and 0.1 mg/m3 over 30 second on average. The applications of the designed spectrometer in measuring the benzene concentration in the air from a moving vehicle and in natural gas are exemplified.
When benzene is determined in oil, naphtha or gasoline, an additional evaporator related with the analytical cell is used. The measurement procedure is rather simple - 10-100 ml of the sample is set in a quartz spoon, which is immediately inserted into the evaporator. The temperature of the evaporator is about 50*C. At this temperature, benzene is evaporated without destruction. Further, benzene vapors with other evaporated constituents are transported into the analytical cell by a carrier-gas, e.g. by air, and the benzene concentration is measured in the cell using Zeeman spectrometry. The detection limit of the proposed analytical system is 0.01% and the maximal measurable concentration is 100%. The advantages of the developed analytical system in comparison with known techniques (GC and IR spectrometry) are high productivity (30 samples/hour compared to 2 - 5 samples/hour), simplicity, and stability of calibration.