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Gas chromatography-atomic emission spectroscopy for metal-selective detection
Abstract
The goal of this dissertation is to develop applications for metal selective gas chromatographic detection by microwave-induced plasma atomic emission spectroscopy. A new commercial GC-AED system is used in the examination and analysis of a wide variety of metal-containing compounds. The performance of the GC-AED for selective detection of model compounds containing aluminum, gallium, chromium, vanadium, cobalt, nickel, palladium and copper is evaluated. Figures-of-merit are reported for these compounds. For aluminum, gallium, chromium, vanadium and palladium, new recipes are developed for the AED concerning digital filters for continuous background correction and experimental parameters such as emission wavelength, helium flow rate and reagent gases, as well as discharge tube materials. The separations of the diastereoisomers of VO(pnTFA$\sb2$) are demonstrated by both capillary GC and HPLC. GC-AED proved valuable in the study of gas phase diastereoisomerism of the tetradentate oxovanadium Schiff base chelates. Picogram detection limits for vanadium by GC-AED facilitated study of kinetic behavior at low concentrations. Multielement detection for metal and nonmetals in the chelates provided identification of eluted peaks. HPLC coupled with DCP and PDA detection assisted the study of the isomerization in solutions. Methods are developed for the characterization of chromium $\beta$-diketone polymers by GC-AED and GC-MS following pyrolysis. Thermal stability is reported for a series of chromium and cobalt chelates and their polymers. Element specific detection proved to be superior in screening metal-containing pyrolysates and simplifying the interpretation of other fragments. High temperature GC-AED is developed for the analysis of vanadyl, nickel and iron porphyrins in crude oils. Limits of detection, precision and inter-element selectivity between vanadium, nickel and iron are reported. The metal elution profiles are characteristic for different oils and compatible for fingerprinting the oils from different fields. The method is also advantageous in the study of decomposition of petroleum metal species. Quantification of the metal profiles indicates the contents of the distillable metals to be generally lower than those of total metals determined by the direct spectroscopic methods. A study on the distribution of metalloporphyrins in crude oils is also carried out by gel permeation chromatography. A correlation between total metal, metalloporphyrin and total distillable metal contents is addressed in this study. Sample pretreatment procedures to remove heavy oil matrices prior to the GC-AED analysis are investigated. Solvent extraction in combination with solid phase extraction is used to extract volatile metal species favorably. GPC proved to be even more effective and reproducible in the resolution of volatile metal species into clean and defined fractions.
Subject Area
Analytical chemistry
Recommended Citation
Zeng, Yadi, "Gas chromatography-atomic emission spectroscopy for metal-selective detection" (1993). Doctoral Dissertations Available from Proquest. AAI9316730.
https://scholarworks.umass.edu/dissertations/AAI9316730