Date of Graduation
Eberly College of Arts and Sciences
Fred L. King.
Elemental speciation analysis is very important because the toxicity of the elements is dependent on their chemical structures. The coupling of Gas Chromatography (GC) with pulsed Glow Discharge Time-of-Flight Mass Spectrometry (GDToFMS) provides real time speciation of volatile organic selenium compounds. The millisecond pulsed glow discharge is a versatile ion source for the determination of elemental composition, molecular structure, and molecular identification. The utility of this ion source to monitor a mixture of the selenium compounds dimethyl selenide (DMeSe) and dimethyl diselenide (DMeDSe) is illustrated in this work. Following the separation by GC, the compounds are readily characterized by pulsed GDToFMS. Time-gated acquisition provides unique information from three separate time regimes---elemental composition from the prepeak, structural fragments from the plateau, and intact molecular identification from the afterpeak.;Distinguishing and quantifying the specific oxidation states of elements are very hard to achieve for solid samples since specific extraction procedures tend to change the speciation. Therefore direct speciation in solid materials is highly desired. In the present work, a pulsed glow discharge time of flight mass spectrometry method is developed for the direct speciation of chromium in solid state samples. Careful tuning of the operating parameters yields the plasma chemistry that favors cluster ion formation. Unique mass spectral features permit differentiation between the trivalent and hexavalent forms of chromium, (CrIII) and (CrVI) respectively, in chromium oxide samples. Specifically, signals at 104 and 120 m/z corresponding to the Cr2 + and Cr2O+ cluster ions are indicative of the presence of Cr(III) in the sample, whereas signal at 100 m/z corresponding to the CrO3+ cluster ion is indicative of the presence of Cr(VI). The impact of glow discharge operating conditions on the appearance of these characteristic cluster ions is discussed.;Also, pulsed glow discharge Time-of-Flight mass spectrometry is used to differentiate between manganese (IV) dioxide and manganese (II) monoxide in solid sample directly. Under certain conditions, the specific cluster ions Mn2O3+ can be produced in the manganese (IV) dioxide glow discharge plasma. The spatial and temporal characteristics of glow discharge source are evaluated and optimized. The glow discharge operating parameters, such as the glow discharge gas pressure and the glow discharge operating power are studied and optimized. After optimizing all the related parameters, the two oxides can be differentiated easily and quantitative analysis was performed successfully.
Zhang, Na, "Elemental speciation using pulsed Glow Discharge Time-of-Flight Mass Spectrometry" (2009). Graduate Theses, Dissertations, and Problem Reports. 2849.