Analysis of brominated compounds in background air by gas chromatography-high-resolution mass spectrometry

The application of a gas chromatography-high-resolution mass spectrometry (GC-HRMS) system to the detection and quantitative analysis of bromine-containing compounds in the Earth's atmosphere is described. By this technique, air samples are introduced to the HRMS system by GC while the HRMS system is tuned to the exact masses of the ions expected in the electron impact spectrum of each compound. By the method described here, the mass spectrometer is assured of focusing precisely on the centroid of the exact mass selected because the mass scale is continuously (two times per second) recalibrated during the chromatographic analysis using n-dodecane as a mass reference. By this technique, the positive identification and quantitative analysis of several brominated compounds consistently found in the background air of rural Montana is demonstrated. In addition, a large volume standard addition technique is described and shown to be well-suited to the quantitative analysis of atmospheric components that have extremely low concentrations. Most of the brominated compounds identified here are present in background air at the sub parts-per-trillion (ppt) level. One of them, CF2Br2, is shown to have an atmospheric presence of only about 40 parts per quadrillion (ppq). Detection limits for all of the brominated compounds identified here were very low (in the low ppq range) and even lower detection limits could be achieved, if desired, by use of sample volumes that are larger than those routinely used here (340 cm(3)). (C) 1999 Elsevier Science B.V. All rights reserved.