Michelle M. Bushey

Butyl acrylate porous polymer monoliths in fused-silica capillaries for use in capillary electrochromatography

Capillary electrochromatography incorporates features of both capillary electrophoresis and liquid chromatography. Butyl acrylate polymers, cast in-situ with heat initiated polymerization and no retaining frits have been made. Van Deemter plots of chrysene have been examined at a variety of operating temperatures to examine column behavior. Hmin moves to faster flow-rates and increases slightly in magnitude as temperature is increased. The longevity and reproducibility of the columns have been examined with a homologous series. Performance is very reproducible between two different columns of different diameters, operated on different systems and prepared from the same polymeriation batch. The relative standard deviation of retention factors is a maximum of 3.1% with most values calculated at less than 1%. The uniformity of the polymers as a function of length has also been studied with a series of polycyclic aromatic hydrocarbons, and the columns have proved to be very uniform across their length as measured by the consistency of retention factors with a maximum relative standard deviation of 3.4% and most values calculated between 1 and 2%. Plate numbers of between 65000 and 80000 plates/m have been attained for compounds with retention factors of 3 to 12. These columns have proved easy to make, are quite reproducible, and long lived.

Measurement of bilirubin partition coefficients in bile salt micelle/aqueous buffer solutions by micellar electrokinetic chromatography.

The partition coefficients for the distribution of bilirubin between aqueous phosphate‐borate buffer and cholic, taurocholic, taurodeoxycholic, and taurochenodeoxycholic micelles have been measured by micellar electrokinetic chromatography at pH 8.5. Determination of the partition coefficients required that the critical micelle concentration and partial specific volumes be determined for each bile salt. Critical micelle concentrations were slightly higher for the trihydroxy bile salts. Partial specific volumes of the bile salt micelles differed very little from each other, and for each bile salt they were constant over the concentration range studied, which was typically from slightly above the critical micelle concentration to 35 mM. Capacity factors were corrected for the effects of applied voltage by extrapolation of the capacity factor to zero applied volts. The free solution mobility of bilirubin, determined in the absence of bile salt, was also corrected for the effects of applied voltage. Plots of extrapolated capacity factor versus phase ratio yield the partition coefficient as the slope of a linear fit to the data. Partition coefficients for bilirubin were significantly higher for dihydroxy bile salts than for trihydroxy bile salts.

Micellar electrokinetic capillary chromatography analysis of the behavior of bilirubin in micellar solutions

The capacity factor of bilirubin is determined by micellar electrokinetic capillary chromatography (MECC) techniques in three different surfactant systems. The capacity factor of bilirubin in cholic acid, taurocholic acid, and taurochenodeoxycholic acid solutions are compared to each other as a function of pH. The pH range studied is 6.5 to 9.5 which includes the pH range of bile, and includes the most likely pKa values of bilirubin carboxyl groups. MECC techniques are used to estimate these apparent pKa values for bilirubin as well as to determine the capacity factors for the separate ionization states of bilirubin in the three different surfactants. Due to the complexity of the bilirubin-bile salt system, it appears as though it is not possible to use MECC to accurately determine the bilirubin apparent pKa values. Separations are performed in 75 microns capillaries, typically 36 to 52 cm in length. UV detection, electrokinetic injection, and run voltages of 7 kV are typical. Solutions of 25 mM of each bile salt are prepared in a 20 mM phosphate-borate buffer system.

Bile salt micellar electrokinetic chromatography of bilirubin and related compounds.

The interaction of bilirubin, biliverdin, bilirubin dimethyl ester, biliverdin dimethyl ester, xanthobilirubic acid, and xanthobilirubin methyl ester with trihydroxy and dihydroxy bile salt solutions is investigated by micellar electrokinetic chromatography (MEKC). The capacity factor of each compound is measured in solutions of the different bile salts over the pH range of 6.5-9.0. The capacity factor of bilirubin increases with pH below 7 in all bile salt solutions. Biliverdin and xanthobilirubin show essentially identical capacity factors for all bile salts. Biliverdin dimethyl ester and xanthobilirubin methyl ester also have very similar capacity factors, which are greater than those of the carboxy analogs, in trihydroxy bile salts. The capacity factors of these esters are higher in the dihydroxy bile salts, with the capacity factor of biliverdin dimethyl ester being twice that of xanthobilirubin methyl ester. Factors involved in the MEKC analysis of these compounds are discussed.

Micellar electrokinetic chromatography of tri aza aromatic ligand compounds of iron (II): influence of bile salt type on enantiomeric separation.

Micellar electrokinetic chromatography is used with a variety of bile salt micelles to separate the enantiomers of bis(8‐((pyridine‐2‐methylene)amino)quinoline)iron(II) hexafluorophosphate, Fe(PMAQ)2(PF6)2; bis(8‐((pyridine‐2‐methylene)amino)lepidine iron(II) hexafluorophosphate, Fe(PMAL)2(PF6)2; and bis(1‐(2‐pyridinyl)ethylidine)‐8‐aminoquinoline iron(II) hexafluorophosphate, Fe(PEAQ)2(PF6)2. The influence of ten different bile salts on the resolution of each pair of enantiomers is investigated. Significant changes in resolution are seen depending upon the bile salt used. The dihydroxy bile salts are superior to the trihydroxy bile salts in terms of resolution, and the taurine or glycine conjugated bile salts yield better results than the unconjugated bile salts. Resolution for most enantiomers is maximized in a buffer solution containing 10–15% acetone and employing either taurochenodeoxycholic or glycochenodeoxycholic acid as the bile salt. Evidence for the separation of the corresponding Fe(III) complexes is presented.

Developing Scientific Literacy in Introductory Laboratory Courses: A Model for Course Design and Assessment

ABSTRACT Although science educators at all levels have focused on teaching students scientific literacy for nearly five decades, studies indicate that the average student remains far from scientifically literate. To address this issue at the local level, faculty at Trinity University, in San Antonio, Texas, significantly revised the curriculum of an existing introductory physical geology laboratory course. The course, which satisfies general education requirements at Trinity, was revised to provide students learning opportunities in a scientific process context as part of a new science literacy initiative. This effort was spurred by general dissatisfaction with the existing curricular structure of the course as well as a new interdisciplinary, National Science Foundation (NSF)–funded initiative to support the integration of research-grade instrumentation in curricula and undergraduate research across campus. The physical geology laboratory course revision was based on research that demonstrated the efficacy of learning through active participation, interpretation, iteration, and reflection, especially when knowledge and skills are gained within an explicit scientific process context. In addition to significantly revising laboratory activities, we added new activities within the course framework that involved the use of two new, NSF-funded instruments, including a handheld X-ray fluorescence spectrometer (XRF) and an inductively coupled plasma–optical emissions spectrometer (ICP-OES), which we used to improve student understanding of qualitative and quantitative elemental analyses. Finally, we introduced the use of a new course reader that provided both background materials for each activity as well as a new focus on providing a scientific process context for students. To assess student learning, we used in-class observations, student–instructor discussions, pre- and postlearning questionnaires, prelaboratory quizzes, course activities completed during class time, modified postactivity reflection questions, practical examinations, and a final examination. We also included faculty, staff, and administrator perspectives to qualitatively assess the impact of course changes upon student learning. Our results imply that students achieved the primary learning goals we developed for this scientific literacy initiative, including: (1) improved understanding of the scientific process and the nature of science; (2) improved understanding of qualitative and quantitative elemental research methods; and (3) improved understanding of the applicability of scientific research to real-world problems. Importantly, our findings suggest that the integration of research-grade instrumentation into introductory coursework, in a scientific process context, is an effective way to promote scientific literacy as well as to provide opportunities for students to understand and apply the knowledge and skills necessary to perform scientific research. We believe that this example of a significant course redesign provides a model that can be transferred to other geosciences departments as well as to other scientific disciplines.

Peak parking determination of the obstruction factor in lauryl acrylate monolithic CEC columns

The peak parking method was used to determine the obstruction factor of lauryl acrylate porous polymer monoliths. Polymers were prepared in situ in fused‐silica capillaries using thermally initiated polymerization. These columns have been used for CEC of neutral analytes. Thiourea, which is unretained, was used as the test analyte for the obstruction factor measurement. The obstruction factor was determined to be 0.72 with a SD of (±0.01), which is consistent with the concept that organic porous polymer monoliths are more permeable than traditional LC stationary phases.

Flame Atomic Absorption Spectroscopy in the Undergraduate Laboratory: Assessment of a NSF‐CCLI Supported Project. What Did the Students Learn and What Did We Learn?

Abstract In traditional chemistry curricula, students may encounter a particular instrument only once in their undergraduate career. We have developed an approach that exposes students multiple times to selected instruments, with early encounters focusing on fundamental aspects of the techniques and later encounters building in complexity and sophistication. We recently finished the assessment phase of a curricular project centered on the incorporation of flame atomic absorption spectroscopy throughout the undergraduate chemistry curriculum. Our assessment indicates that this approach is successful and our initial goals were largely achieved.

MICELLAR ELECTROKINETIC CHROMATOGRAPHY OF BILIRUBIN AND RELATED COMPOUNDS IN UNCONJUGATED AND GLYCO-CONJUGATED BILE SALT SOLUTIONS

The interactions of bilirubin, biliverdin, xanthobilirubin, biliverdin dimethyl ester, and xanthobilirubin methyl ester with unconjugated and glyco-conjugated bile salt solutions were investigated by micellar electrokinetic chromatography (MEKC). The capacity factors were measured in solutions of the different bile salts over the pH range of 6.5 to 8.5. The bile salts investigated were deoxycholic, chenodeoxycholic, glycocholic, glycodeoxycholic, and glycochenodeoxycholic acid. These results were compared to previous results in cholic, taurocholic, taurodeoxycholic, and taurochenodeoxycholic acids. Typically, the nature of the bile salt, trihydroxy versus dihydroxy, has a greater effect on the resulting capacity factors than does the nature of the conjugation. The influence on capacity factor of such features as molecular size, shape, and charge are revealed with this group of analytes.