Application of multicapillary columns for the fast separation of BTEX aromatic hydrocarbons from ambient air samples

Air pollution affects public health and the environment, and must be controlled. Measurement of the spatial distribution of pollutants by a mobile laboratory requires fast response of the analytical instruments used. Optical methods of detecting nitrogen oxides, suspended particles, ozone, sulfur dioxide and carbon monoxide in the air allow performing up to 10 measurements per second. Determination of the content of aromatic hydrocarbons (benzene, toluene, ethylbenzene and xylenes, collectively designated as BTEX) is carried out by mass spectrometry and gas chromatography. However, a mass spectrometer is rarely used due to its high cost, and existing automatic gas chromatographs perform BTEX measurements in ca. 15 min, which is unacceptable for the mobile posts. Such time is required due to the use of capillary or packed columns for chromatographic separation. In the present study the possibility of reducing the separation time using multicapillary columns (MCC) is investigated. High capacity of MCC in respect to sample volume eliminates the need for multi-stage sample concentration or column temperature programming. A separation scheme with semi-back flushing from two sequential columns was used employing a short column with non-polar and a long column with polar stationary phases. This allowed excluding peaks of non-polar substances from the region of BTEX peaks, which simplified the chromatogram appearance and reduced the requirements to column efficiency. A photoionization detector with a krypton lamp was used as a detector. It was experimentally shown that the proposed scheme with two MCCs allows isolation of BTEX hydrocarbons during the analysis of real air samples within ca. 1.5 min. The use of MCC as part of an automatic gas chromatograph for a mobile laboratory is recommended for measuring BTEX in the atmospheric air.