Robert J. Hurtubise

Retention characteristics of several compound classes in reversed-phase liquid chromatography with β-cyclodextrin as a mobile phase modifier

Abstract β-Cyclodextrin was investigated as a mobile phase modifier in the reversed-phase liquid chromatography of polycyclic aromatic hydrocarbons, nitrogen hetero-cycles and hydroxyl aromatics. A wide range of β-cyclodextrin concentrations was employed, and the retention properties of the compound classes were compared in methanol—water and ethanol—water mobile phases at 25°C. β-Cyclodextrin—solute dissociation constants were obtained for the compounds in several methanol—water and ethanol—water mobile phase compositions, using the chromatographic data. The trends in the retention data and dissociation constants for the compound classes were discussed. Several conclusions were drawn concerning the mechanism of retention when β-cyclodextrin is present in the mobile phases. Also, comparisons were made between the structural features of the compounds and their capacity factors and dissociation constants.

Room-Temperature Luminescence of Several Compounds on an α-Cyclodextrin-NaCl Mixture

Fifty-five organic compounds of various sizes and functionalities were investigated for solid-surface room-temperature fluorescence (RTF) and phosphorescence (RTP) on an 80% α-cyclodextrin-NaCl matrix. Forty-two of these compounds showed either RTP and/or RTF on this matrix. The relative RTP intensities of the compounds were compared, and the results showed that triphenylene gave the strongest RTP signal, while phenanthridine gave the weakest signal. The range of the RTP limit of detection of the phosphorescent compounds on an 80% α-cyclodextrin-NaCl mixture was determined to be between 0.2 ng and 15 ng. The results showed the general analytical potential of this approach because of the large number of compounds yielding luminescence signals and the selectivity and sensitivity achieved.

A study of the interactions of benzo[f]quinoline, quinoline and phenanthrene by infrared and reflectance spectroscopy and the relationship to room-temperature phosphorescence

Abstract Reflectance spectroscopy is used to provide evidence for the forms of benzo[f]quinoline and quinoline adsorbed on filter papre, silica gel chromatoplates, and 0.5% polyacrylic acidNaCl mixture. Infrared data suggest several hydrogen bonding interactions for benzo[f]quinoline and phenanthrene with polyacrylic acid-salt mixtures. With the reflectance and infrared data, a partial model for phosphor/solid surface interaction was developed for the compounds; this model should be useful in room-temperature phosphorescence work.

Solid-matrix luminescence analysis: photophysics, physicochemical interactions and applications

Abstract Solid-matrix luminescence spectrometry (SMLS) has become an established approach for the trace analysis of organic compounds, and more recently, for several inorganic species. A rather large amount of photophysical data has been obtained from lumiphors adsorbed on solid matrices. However, these data have not been compared nor discussed in detail. In this review, fluorescence quantum yields and phosphorescence quantum yields for several lumiphors adsorbed on solid matrices are considered. Also, a number of solid-matrix luminescence quantum yield values are compared to solution quantum yield values. Both fluorescence and phosphorescence lifetimes are contrasted for lumiphors on solid matrices and lumiphors in solution. Several fundamental photophysical equations are presented. The discussion centers around how the equations can be used to calculate basic photophysical rate constants for compounds adsorbed on solid matrices. Photophysical rate constants for fluorescence and phosphorescence and intersystem crossing are compared in some detail. Several recent advances in physicochemical interactions are considered in light of recent data. The importance of rigidity in SML, the effects of moisture and gases in SML, the effects of heavy atoms in SML, the role of the heat capacity in SML, and other parameters are discussed. Recent applications, with emphasis on solid-matrix phosphorescence (SMP), are also presented.

Mechanistic Aspects of the Oxygen Quenching of the Solid-Matrix Phosphorescence of Perdeuterated Phenanthrene on Partially Hydrophobic Paper

The effects of oxygen over a wide concentration range on the solid-matrix phosphorescence (SMP) of perdeuterated phenanthrene (D10) adsorbed on partially hydrophobic paper (1PS) were investigated. The SMP lifetime results of D10 adsorbed on Whatman 1PS paper and Whatman No. 1 paper were considered, and the SMP intensities and SMP lifetimes of D10 on 1PS paper were compared. The SMP quenching model employed showed that diffusional quenching was not very extensive for D10 adsorbed on both types of paper. In addition, a large fraction of the D10 phosphor molecules did not undergo diffusional quenching in either paper. The changes in the SMP intensities for D10 adsorbed on 1PS paper were much greater than the corresponding SMP lifetime changes, which indicated that static quenching by oxygen was very effective for D10 on 1PS paper. Also, the SMP intensity data indicated that a relatively large fraction of the D10 molecules were not quenched statically. The quenching data were interpreted and compared with equations that permitted both linear and nonlinear models to be employed.

Determination of ionization constants of heterocyclic aromatic amines using capillary zone electrophoresis

Abstract Capillary zone electrophoresis (CZE) is a very convenient technique for the determination of ionization constants. The technique is rapid, precise, uses small quantities of solute, and the exact concentration of the compound is not needed. This work represents the first report on the ionization constants of eight heterocyclic aromatic amines: 2-amino-1-methyl-6-phenylimidazo[4,5- b ]pyridine, 2-amino-9H-pyrido[2,3- b ]indole, 3-amino-1-methyl-5H-pyrido[4,3- b ]indole acetate, 2-amino-3-methyl-3H-imidazo[4,5- f ]quinoline, 2-amino-3,8-dimethylimidazo[4,5- f ]quinoxaline, 2-amino-3,4,8-trimethyl-3H-imidazo[4,5- f ]quinoxaline, 2-amino-3,4,7,8-tetramethyl-3H-imidazo[4,5- f ]quinoxaline and 9-H-pyrido[4,3- b ]indole. The ionization constants determined using CZE were confirmed with independent determinations by ultraviolet spectrometry.

The effects of temperature on the solid-surface luminescence properties of benzo(f)quinoline adsorbed on filter paper

Experimental values of fluorescence quantum yield, phosphorescence quantum yield, and phosphorescence lifetime were acquired at temperatures from 23° to −180°C for the protonated form of benzo(f)quinoline adsorbed on filter paper. From the experimental values, triplet formation efficiencies, rate constants for phosphorescence, and rate constants for the radiationless transition from the triplet state were calculated. The results showed the various interrelationships of the solid-surface radiative and nonradiative processes. In addition, the results indicated that the modulus of the solid matrix is an important factor in enhancing phosphorescence quantum yield.

Solid-Phase microextraction with Whatman 1PS paper and direct room-temperature solid-matrix luminescence analysis.

Solid-phase microextraction has been combined with solid-matrix luminescence for the detection of a variety of compounds at sub-nanogram levels for the first time. Whatman 1PS paper was placed in water solutions of polar and nonpolar compounds for the selective removal of the nonpolar compounds such as benzo(a)pyrene. Distribution constants were obtained for 4-phenylphenol, benzo(f)quinoline, benzo(h)quinoline, phenanthrene, and benzo(a)pyrene. The distribution constants showed that phenanthrene and benzo(a)pyrene in water had a very strong affinity for the 1PS paper. Once the solutes were extracted for a fixed period of time, the 1PS paper was dried, and either the solid-matrix fluorescence or solid-matrix phosphorescence was detected from the adsorbed lumiphors by using the appropriate excitation wavelengths. It was a simple matter to detect at least three adsorbed compounds on the 1PS paper by solid-matrix luminescence. Benzo(a)pyrene was easily detected at a level of 0.02 ng ml(-1) in water.

Room-Temperature Luminescence Properties of p-Aminobenzoic Acid and 4-Phenylphenol Adsorbed on α-Cyclodextrin/NaCl Mixtures

The solid-surface fluorescence and phosphorescence quantum yield values and phosphorescence lifetime values were obtained for p-aminobenzoic acid (PABA) and 4-phenylphenol adsorbed on α-cyclodextrin/NaCl mixtures. From the luminescence quantum yield and phosphorescence lifetime data, the triplet formation efficiency values, the phosphorescence rate constants, and the rate constants for radiationless transition from the triplet state were determined for PABA and 4-phenylphenol on α-cyclodextrin/NaCl mixtures. In addition, the percentages of radiative and nonradiative transitions were calculated for the two compounds. The various luminescence parameters obtained in this work provided important insights into the analyte/α-cyclodextrin substrate interactions responsible for the observed solid-surface room-temperature fluorescence (RTF) and phosphorescence (RTP). Furthermore, the RTF and RTP intensities of PABA and 4-phenylphenol were obtained from several α-cyclodextrin/NaCl mixtures. These data showed the importance of the initial wet chemistry in the sample preparation procedure.

The effects of adsorption of solutes on glassware and teflon in the calculation of partition coefficients for solid-phase microextraction with 1PS paper.

Solid-phase microextraction presents numerous advantages over traditional extraction techniques. However, the determination of partition coefficients is not as simple as it may appear. For very nonpolar compounds, such as polycyclic aromatic compounds, adsorption to the glass wall of the extraction vial and the Teflon coating of the stir bar may be quite significant. These interactions must be taken into account when calculating partition coefficients. Failing to do this may lead to large errors in the value of the partition coefficient, particularly for very nonpolar compounds. Three polar compounds and seven polycyclic aromatic hydrocarbons were partitioned individually between Whatman 1PS paper and water solutions of the compounds. The partition coefficiencts were calculated with two equations, and detailed mass balance data were acquired for the adsorption of the solute on the stir bar, glass vial, and 1PS paper. The mass data were compared with the partition coefficients, and important conclusions were made about the practical use of the partition coefficients.