Quantification of Aromatic and Halogenated Hydrocarbons and Alcohol Mixtures at the Elemental, Structural, and Parent Molecular Ion Level Daniel Fliegel, Ruth Waddell, ‡ Vahid Majidi, ‡ Detlef Gu1 nther, and Cris L. Lewis* ,‡ Laboratory for Inorganic Chemistry, Swiss Federal Institute of TechnologysZurich, CH-8093 Zurich, Switzerland, and Analytical Chemistry Sciences, MS K484, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 The capabilities of a millisecond pulsed glow discharge time-of-flight mass spectrometer for the quantitative analy- sis of organic molecules were investigated. Mixtures of analytes were separated by gas chromatography, and mass spectra were collected at three different time regimes during the pulse cyclesthe prepeak, plateau, and after- peak time regimes. Elemental information was collected in the prepeak, structural information in the plateau, and molecular ion information in the afterpeak. A sample mixture containing toluene, o-xylene, o-dichlorobenzene, and a binary mixture of methanol and sec-butanol were considered. Calibration curves were constructed for each time regime based on the intensities of the elemental, fragment, and molecular ions. Optimum linearity (r 2 ) 0.999) was achieved during the plateau time regime, although calibration in the prepeak was also demon- strated, albeit with slightly poorer correlation coefficients (r 2 > 0.959). The minimum limits of detection (MDL) were 392, 422, and 557 ng, for toluene, o-xylene, and o-dichlorobenzene, respectively, using a 3-μL injection and a split ratio of 68:1. For the binary alcohol mixture, MDLs of 1.87 and 2.44 μg were determined for methanol and sec-butanol, respectively, based on the intensity of the 16 O + ion during the prepeak and using a split ratio of 58:1. Chemical speciation is of increasing importance in many fields of analytical, environmental, pharmaceutical, and nutritional chemistry. Analysts in these fields are increasingly required to evaluate an analyte in several different dimensions, for example, at the elemental, isotopic, structural level, or even unfragmented parent ion. Evaluation of such information in a timely manner with minimal sample consumption is one of the most challenging tasks facing analysts today. Chemical speciation analysis often involves hyphenated techniques that couple an ionization source, such as electron impact or chemical ionization (CI), to a separation technique, such as gas or liquid chromatography (GC or LC). 1-5 Unfortunately, these sources do not provide the analyst with elemental, structural, and intact parent molecular ions simulta- neously. Several reports have demonstrated that techniques can be optimized to gain access to one or two dimensions of analyte information. For example, the elemental and isotopic composition of analytes can be determined rapidly and with high precision using inductively coupled plasma mass spectrometry (ICPMS). 6 ICPMS can also be applied to a wide variety of sample matrixes such as liquids, 7 gases, and particles, 8-10 with limits of detection in the subnanogram per kilogram range for most elements. How- ever, the plasma power of the ICP source is typically greater than 1000 W, often resulting in complete atomization of the sample. Consequently, the detection of structural and parent molecular information is not possible without manipulating the ICP power. There have been several approaches that describe “tuning” the plasma conditions to obtain both elemental and structural informa- tion simultaneously. 11-16 However, to date, no tuned plasma has demonstrated intact parent molecular ions solely and separately from the corresponding elemental or structural ions. 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