Direct atmospheric pressure chemical ionization-tandem mass spectrometry for the continuous real-time trace analysis of benzene, toluene, ethylbenzene, and xylenes in ambient air

Abstract

Real-time monitoring of benzene, toluene, ethylbenzene, and xylenes (BTEX) in ambient air is essential for the early warning detection associated with the release of these hazardous chemicals and in estimating the potential exposure risks to humans and the environment. We have developed a tandem mass spectrometry (MS/MS) method for continuous real-time determination of ambient trace levels of BTEX. The technique is based on the sampling of air via an atmospheric pressure inlet directly into the atmospheric pressure chemical ionization (APCI) source. The method is linear over four orders of magnitude, with correlation coefficients greater than 0.996. Low limits of detection in the range 1-2 g/m 3 are achieved for BTEX. The reliability of the method was confirmed through the evaluation of quality parameters such as repeatability and reproducibility (relative standard deviation below 8% and 10%, respectively) and accuracy (over 95%). The applicability of this method to real-world samples was evaluated through measurements of BTEX levels in real ambient air samples and results were compared with a reference GC-FID method. This direct APCI-MS/MS method is suitable for real-time analysis of BTEX in ambient air during regulation surveys as well as for the monitoring of industrial processes or emergency situations. B enzene, toluene, ethylbenzene, and isomers of xylene, commonly called BTEX, are volatile organic compounds (VOCs) widely present in petroleum products and added to fuels to increase their octane number [1]. They have toxic health effects depending on duration and levels of exposure [2][3][4][5]. In addition, BTEX in urban air contribute significantly to the smog photochemical reactions leading to ozone formation in the troposphere [6].Several analytical methods have been developed to perform real-time measurements of such compounds in ambient air, and recently, we have published a comprehensive review of the most commonly used on-site methods for continuous real-time monitoring of airborne VOCs [7]. Differential optical absorption spectroscopy (DOAS) has been applied widely for near real-time monitoring of BTEX in ambient air [8,9], but the presence of oxygen, ozone, and several hydrocarbons with similar spectra gives rise to severe interference effects.Proton-transfer reaction/mass spectrometry (PTR-MS) has been used in several field studies for real-time monitoring of atmospheric BTEX [10,11], but there are certain isobaric interferences in the PTR-MS measurements of these hydrocarbons (e.g., notably benzaldehyde).Other direct-air sampling (DS)-MS methods widely used for real-time determination of BTEX in ambient air are low-pressure chemical ionization/tandem mass spectrometry (LPCI-MS/MS) [12,13] and atmospheric pressure chemical ionization/tandem mass spectrometry (APCI-MS/MS) [14,15]. However, they are not yet very conclusive for measuring BTEX in ambient air at low-g/m 3 concentrations [7].The work described in the present article demonstrates the application of a direct APCI-MS/MS system for real-ti...

Observation of Replacement of Carbon in Benzene with Nitrogen in a Low-Temperature Plasma

“…The reaction product was on-line monitored using a high resolution Orbitrap mass spectrometer. Besides the peaks at mass-over-charge ratio (m/z) 94.0651 (C 6 H 8 N + ), 110.0600 (C 6 H 8 ON + ) and 126.0551 (C 6 H 8 NO 2 + ), the most abundant ionic species observed was m/z 80.0494 (Figure 1A), which was different from the typical molecular ion of benzene (m/z 78.0469) as shown in Figure S2 in mass spectrometry (MS) analysis16. In a previous study under a similar plasma condition but with benzene in helium, ion [M + 2] + was observed and was identified as C 6 H 8 + based on deuterium isotopic labeling experiments15.…”

Differentiation of Regioisomeric Aromatic Ketocarboxylic Acids by Positive Mode Atmospheric Pressure Chemical Ionization Collision-Activated Dissociation Tandem Mass Spectrometry in a Linear Quadrupole Ion Trap Mass Spectrometer

“…CAD-based MS n techniques have been applied to the characterization of unknown substances in many fields, including the pharmaceutical industry [19,20], and research on chemical warfare agents [21], proteins [22], volatile organic compounds [23], airborne oxidants [24], bacteria, DNA [25,26], and microextracted water samples [27]. Hydrogen/deuterium (H/D) exchange experiments [28][29][30] and molecular orbital calculations [31,32] have facilitated the differentiation of isomeric compounds.…”

Direct Analysis Mass Spectrometry

“…Direct APCI in combination with tandem mass spectrometry was applied to the real-time monitoring of benzene, toluene, ethylbenzene, and xylenes in ambient air. The method was linear over four orders of magnitude with a sensitivity of 0.5 ppbv (2 µg m − 3 ) [17]. A similar study using a hand-held mass spectrometer and APCI source achieved limits of detection for benzene, toluene, and ethylbenzene of around 0.5 ppbv [18].…”