Analysis of N-nitrosames in water using micellar electrokinetic chromatography (MEKC) and development of online and offline methods of extraction and enrichment of neutral polar analytes

Evaluation of the quality of the environment is essential for human wellness as pollutants in trace amounts can cause serious health problem. Nitrosamines are a group of compounds that are considered potential carcinogens and can be found in drinking water (as disinfection byproducts), foods, beverages and cosmetics. To monitor the level of these compounds to minimize daily intakes, fast and reliable analytical techniques are required. As these compounds are relatively highly polar, extraction and enrichment from environmental samples (aqueous) are challenging. Also, the trend of analytical techniques toward the reduction of sample size and minimization of organic solvent use demands new methods of analysis. In light of fulfilling these requirements, a new method of online preconcentration tailored to an electrokinetic chromatography is introduced. In this method, electroosmotic flow (EOF) was suppressed to increase the interaction time between analyte and micellar phase, therefore the only force to mobilize the neutral analytes is the interaction of analyte with moving micelles. In absence of EOF, polarity of applied potential was switched (negative or positive) to force (anionic or cationic) micelles to move toward the detector. To avoid the excessive band broadening due to longer analysis time caused by slow moving micelles, auxiliary pressure was introduced to boost the micelle movement toward the detector using an in house designed and built apparatus. Applying the external auxiliary pressure significantly reduced the analysis times without compromising separation efficiency. Parameters, such as type of surfactants, composition of background electrolyte (BGE), type of capillary, matrix effect, organic modifiers, etc., were evaluated in optimization of the method. The enrichment factors for targeted analytes were impressive, particularly; cationic surfactants were shown to be suitable for analysis of nitrosamines due to their ability to act as hydrogen bond donors. Ammonium perfluorooctanoate (APFO) also showed remarkable results in term of peak shapes and number of theoretical plates. It was shown that the separation results were best when a high conductivity sample was paired with a BGE of lower conductivity. Using higher surfactant concentrations (up to 200 mM SDS) than usual (50 mM SDS) for micellar electrokinetic chromatography (MEKC) improved the sweeping. A new method for micro-extraction and enrichment of highly polar neutral analytes (N-Nitrosamines in particular) based on three-phase drop micro-extraction was introduced and its performance studied. In this method, a new device using some easy-to-find components was fabricated and its operation and application demonstrated. Compared to conventional extraction methods (liquid-liquid extraction), consumption of organic solvents and operation times were significantly lower.

A study of methods used to analyze total oil and polycyclic aromatic hydrocarbons in produced water: steps towards the validation of molecularly imprinted polymers for use in marine environmetns

Produced water is a by-product of offshore oil and gas production, and is released in large volumes when platforms are actively processing crude oil. Some pollutants are not typically removed by conventional oil/water separation methods and are discharged with produced water. Oil and grease can be found dispersed in produced water in the form of tiny droplets, and polycyclic aromatic hydrocarbons (PAHs) are commonly found dissolved in produced water. Both can have acute and chronic toxic effects in marine environments even at low exposure levels. The analysis of the dissolved and dispersed phases are a priority, but effort is required to meet the necessary detection limits. There are several methods for the analysis of produced water for dispersed oil and dissolved PAHs, all of which have advantages and disadvantages. In this work, EPA Method 1664 and APHA Method 5520 C for the determination of oil and grease will be examined and compared. For the detection of PAHs, EPA Method 525 and PAH MIPs will be compared, and results evaluated. APHA Method 5520 C Partition-Infrared Method is a liquid-liquid extraction procedure with IR determination of oil and grease. For analysis on spiked samples of artificial seawater, extraction efficiency ranged from 85 – 97%. Linearity was achieved in the range of 5 – 500 mg/L. This is a single-wavelength method and is unsuitable for quantification of aromatics and other compounds that lack sp³-hybridized carbon atoms. EPA Method 1664 is the liquid-liquid extraction of oil and grease from water samples followed by gravimetric determination. When distilled water spiked with reference oil was extracted by this procedure, extraction efficiency ranged from 28.4 – 86.2%, and %RSD ranged from 7.68 – 38.0%. EPA Method 525 uses solid phase extraction with analysis by GC-MS, and was performed on distilled water and water from St. John’s Harbour, all spiked with naphthalene, fluorene, phenanthrene, and pyrene. The limits of detection in harbour water were 0.144, 3.82, 0.119, and 0.153 g/L respectively. Linearity was obtained in the range of 0.5-10 g/L, and %RSD ranged from 0.36% (fluorene) to 46% (pyrene). Molecularly imprinted polymers (MIPs) are sorbent materials made selective by polymerizing functional monomers and crosslinkers in the presence of a template molecule, usually the analytes of interest or related compounds. They can adsorb and concentrate PAHs from aqueous environments and are combined with methods of analysis including GC-MS, LC-UV-Vis, and desorption electrospray ionization (DESI)- MS. This work examines MIP-based methods as well as those methods previously mentioned which are currently used by the oil and gas industry and government environmental agencies. MIPs are shown to give results consistent with other methods, and are a low-cost alternative improving ease, throughput, and sensitivity. PAH MIPs were used to determine naphthalene spiked into ASTM artificial seawater, as well as produced water from an offshore oil and gas operation. Linearity was achieved in the range studied (0.5 – 5 mg/L) for both matrices, with R² = 0.936 for seawater and R² = 0.819 for produced water. The %RSD for seawater ranged from 6.58 – 50.5% and for produced water, from 8.19 – 79.6%.

Analysis of bio-derived platform chemicals in ionic liquid media by desorption/ionization mass spectrometry

In this work, desorption/ionization mass spectrometry was employed for the analysis of sugars and small platform chemicals that are common intermediates in biomass transformation reactions. Specifically, matrix-assisted laser desorption/ionization (MALDI) and desorption electrospray ionization (DESI) mass spectrometric techniques were employed as alternatives to traditional chromatographic methods. Ionic liquid matrices (ILMs) were designed based on traditional solid MALDI matrices (2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (CHCA)) and 1,3-dialkylimidazolium ionic liquids ([BMIM]Cl, [EMIM]Cl, and [EMIM]OAc) that have been employed as reaction media for biomass transformation reactions such as the conversion of carbohydrates to valuable platform chemicals. Although two new ILMs were synthesized ([EMIM][DHB] and [EMIM][CHCA] from [EMIM]OAc), chloride-containing ILs did not react with matrices and resulted in mixtures of IL and matrix in solution. Compared to the parent solid matrices, much less matrix interference was observed in the low mass region of the mass spectrum (< 500 Da) using each of the IL-matrices. Furthermore, the formation of a true ILM (i.e. a new ion pair) does not appear to be necessary for analyte ionization. MALDI sample preparation techniques were optimized based on the compatibility with analyte, IL and matrix. ILMs and IL-matrix mixtures of DHB allowed for qualitative analysis of glucose, fructose, sucrose and N-acetyl-D-glucosamine. Analogous CHCA-containing ILMs did not result in appreciable analyte signals under similar conditions. Small platform compounds such as 5-hydroxymethylfurfural (HMF) and levulinic acid were not detected by direct analysis using MALDI-MS. Furthermore, sugar analyte signals were only detected at relatively high matrix:IL:analyte ratios (1:1:1) due to significant matrix and analyte suppression by the IL ions. Therefore, chemical modification of analytes with glycidyltrimethylammonium chloride (GTMA) was employed to extend this method to quantitative applications. Derivatization was accomplished in aqueous IL solutions with fair reaction efficiencies (36.9 – 48.4 % glucose conversion). Calibration curves of derivatized glucose-GTMA yielded good linearity in all solvent systems tested, with decreased % RSDs of analyte ion signals in IL solutions as compared to purely aqueous systems (1.2 – 7.2 % and 4.2 – 8.7 %, respectively). Derivatization resulted in a substantial increase in sensitivity for MALDI-MS analyses: glucose was reliably detected at IL:analyte ratios of 100:1 (as compared to 1:1 prior to derivatization). Screening of all test analytes resulted in appreciable analyte signals in MALDI-MS spectra, including both HMF and levulinic acid. Using appropriate internal standards, calibration curves were constructed and this method was employed for monitoring a model dehydration reaction of fructose to HMF in [BMIM]Cl. Calibration curves showed wide dynamic ranges (LOD – 100 ng fructose/μg [BMIM]Cl, LOD – 75 ng HMF/μg [BMIM]Cl) with correlation coefficients of 0.9973 (fructose) and 0.9931 (HMF). LODs were estimated from the calibration data to be 7.2 ng fructose/μg [BMIM]Cl and 7.5 ng HMF/μg [BMIM]Cl, however relatively high S/N ratios at these concentrations indicate that these values are likely overestimated. Application of this method allowed for the rapid acquisition of quantitative data without the need for prior separation of analyte and IL. Finally, small molecule platform chemicals HMF and levulinic acid were qualitatively analyzed by DESI-MS. Both HMF and levulinic acid were easily ionized and the corresponding molecular ions were easily detected in the presence of 10 – 100 times IL, without the need for chemical modification prior to analysis. DESI-MS analysis of ILs in positive and negative ion modes resulted in few ions in the low mass region, showing great potential for the analysis of small molecules in IL media.