published_or_final_version / Chemistry / Master / Master of Philosophy

This thesis begins with an examination of the feasibility of using the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method, and its variants, for the co-extraction of nonpolar and polar pesticides, including highly polar quaternary ammonium salts (QA) and organophosphates (OP). QuEChERS was performed on a mixture of nine different chemical classes of pesticides, with triphenyl phosphate (TPP) as the internal standard, on aqueous Chinese lettuce samples, at 0.1 and 1.0 μg/mL levels. QuEChERS provided superior sample recovery and precision (RSD) for nonpolar pesticides than it did for its polar variants, including most of the polar pesticides and several carbamates, as judged from quintuplicate analyses. A modification of the extraction buffer and cleanup reagent significantly enhanced the recovery of highly polar QA and carbamates at sub–microgram-per-milliliter levels, while maintaining the performance of the other nonpolar pesticides. Thus, QuEChERS is a versatile and convenient methodology for multi-residue analyses, although unambiguous confirmation and quantification of some polar pesticides, namely chlormequat, mepiquat, and glyphosate, required separate analyses using tedious and time-consuming single-residue methods. Liquid chromatography/tandem mass spectrometry (LC-MS/MS) provides the potential advantages of low detection limits, simple sample preparation procedures, and high selectivities for multi-residue analyses of organic toxics in food. In this study, a novel methodology based on LC-MS/MS was developed for the simultaneous analyses of both polar and nonpolar pesticides; an online-coupled hydrophilic-interaction chromatography/reversed-phase (HILIC-RP) separation platform, featuring a HILIC column for online sample enrichment and a downstream high-flow injector for solvent mixing and reconditioning, was constructed to allow efficient, concomitant analyses of both hydrophilic and hydrophobic pesticides from a single sample injection event. The performance of the HILIC-RP system, verified using a standard pesticide mixture, was satisfactory. 6 out the 7 polar pesticides were successfully retained on the HILIC column and 11 out of the 15 nonpolar pesticides were transferred to and separated by the RP column; the remaining compounds were determined as flow-through prior to the HILIC separation. No sensitivity loss of the polar pesticides was observed when using this hyphenated system. The calibration curves for 20 out of the 22 standard pesticides exhibited excellent linear responses (R2 > 0.995) over a typical working concentration range. The performance of the HILIC-RP platform was comparable with those of individual one-dimensional HILIC and RP analyses, thereby potentially eliminating redundant quantification procedures and allowing highthroughput multi-residue analyses of toxic organic compounds. / published_or_final_version / Chemistry / Master / Master of Philosophy

abstract / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

The competition between two molecules of similar polarity for adsorption sites on the stationary phase is discussed in light of rapid kinetics of adsorption and desorption, and of the effects of temperature, acetonitrile, surfactant (cyclohexylaminopropane sulfonic acid, CAPS) and salt concentrations on the retention of the thyroid hormones (3,5-diiodothyronine, T2; 3,3',5-triiodothyronine, T3 and thyroxine, T4). A three parameter equation relates the surfactant concentration and ionic strength to the retention of the hormones and is analyzed in terms of the Stern-Gouy-Chapman theory. A second order polynomial describes the temperature dependency and permits the evaluation of the enthalpy, entropy and heat capacity, demonstrating a reduction in the molecular motion of the analyte with increasing surfactant and acetonitrile concentrations. The equation parameters for linear or non-linear equations, using data sets with or without homogeneous variances, are evaluated using a Simplex optimization procedure that uses one of two proposed optimization criteria. The construction and operation of a computer based gradient programmer for HPLC is described. A surfactant mediated gradient elution with electrochemical detection is examined for the analysis of serum thyroid hormones.

No description available.

No description available.

Despite the prominent role played by open tubular columns in gas chromatography, they have enjoyed comparatively little success as supports for open tubular liquid chromatography (OTLC), owing to impractical channel diameters (3-5 μm) required to facilitate retention in the liquid phase. In an effort to circumvent the technical issues associated with such narrow diameters, columns with multiple parallel channels have been suggested as alternatives – to this end, micro-structured fibres (MSFs) have been proposed as supports for OTLC. Much research has been conducted using MSFs for chromatography in the Oleschuk group, and although some success has been achieved, performance has been continuously hindered by flow velocity variation among the channels stemming from differences in channel sizes (or channel variance) as well as differences in stationary phase coverage, which serve to degrade column efficiency. Recent efforts have focused on devising a novel method for assessing the channel variance of MSFs. This method seeks to determine hole tolerance through evaluation of the extent of band broadening that occurs when performing chromatography in the absence of a retentive mechanism. Using this method, a linear correlation between the relative standard deviation of the channel diameters and the amount of broadening was revealed. To supplement the results, computational fluid dynamics was employed to simulate fluid flow through multi-channel columns. The results of these simulations again provided a linear correlation between the RSD of the channel diameters and the extent of flow velocity variation among the channels. / Thesis (Master, Chemistry) -- Queen's University, 2012-08-15 11:57:28.915

Selenonium cations are electron deficient species in which the central selenium atom is bonded to three carbon chains (aryl or alkyl). Trimethylselenonium iodide was synthesized by reaction of methyllithium with metallic selenium to produce methylselenolithium which was, in turn, reacted with the appropriate alkylbromide. The selenide thus formed was further methylated at the selenium atom with methyl iodide in methanol in the presence of sodium tetraphenylborate. After several recrystallizations the selenonium analytes were characterized by AAS, FT-IR, $ sp1$H-NMR, $ sp{13}$C-NMR, FAB-MS and LAMMA spectroscopic techniques and used as standards for analytical methods development. / The analysis was performed by high performance liquid chromatography with atomic absorption detection. The chromatography on a cynopropyl silica bonded phase was optimized for mobile phase composition by response surface analysis. The resulting surface response plots permitted a differentiation between the mechanisms of action of two mobile phase modifiers: triethylamine and trimethylsulfonium iodide. The improvement in chromatographic efficiency resulted in two to three fold decrease in the limit of detection. An extraction procedure with liquefied phenol was evaluated for the determination, by HPLC-AAS, of traces of selenonium cations in biological samples. The advantages and shortcomings of the HPLC-THG-AAS approach are discussed.