L. A. Carreira

Fluorescence techniques for metal-humic interactions

SummaryTwo fluorescence techniques to study metal-humic interactions are presented. In the first technique, Lanthanide Ion Probe Spectroscopy (LIPS), the humic samples are titrated by Eu3+ ions. The ratio of the intensities of two emission lines of Eu3+, R=I592/I616, is used to estimate the amount of bound and free species of the probe ions. The titration plot is presented as R versus the logarithm of total added Eu3+. In the second technique, fluorescence quenching of the humic material by Cu2+ is used to produce titration curves of intensity versus the logarithm of total added Cu2+. The two techniques are used in conjunction with a model that treats the various ligands in humic substances as continuous distributions of binding sites in which individual ligand concentrations are normally distributed with respect to the individual stability constants for metal binding. The model includes the effects of pH, ionic strength, and competing metal ions. The parameters of the model are estimated by fitting the spectral titration data to the calculated titration plot. Some simulation and experimental data are presented and discussed.

Continuous, On-Line Interface for Reverse-Phase Microbore High-Performance Liquid Chromatography/Diffuse Reflectance Infrared Fourier Transform Analysis

An ultrasonic nebulizer with a piezo-electric transducer and a newly designed and constructed continuous on-line collection station have been adapted as an interface between a reverse-phase microbore high-performance liquid Chromatograph (RP-μHPLC) and a diffuse reflectance infrared Fourier transform spectrometer. The collection station incorporates a directional vacuum port for confinement of the nebulized material onto a small area (3 to S mm i.d.) of the diamond powder. The inherent desolvation that occurs upon nebulization of the reverse-phase eluant, along with the vacuum collection system and the diamond powder diffuse reflectance substrate, makes possible the continuous on-line collection and FT-IR analysis of the compounds separated by a RP-μHPLC without any type of initial solute extraction.

Fluorescence Studies of Metal-Humic Complexes with the Use of Lanthanide Ion Probe Spectroscopy

The acidic functional groups of humic materials are an abundant source of metal binding sites in the natural environment. Studies of metal binding to humics are of great environmental interest because the biological and physicochemical properties of metals are often changed dramatically as a result of complexation with humics. In order to understand how these heterogeneous organic macromolecules bind metals with such a large range of binding energies, lanthanide ion probe spectroscopy (LIPS) has been used to study changes in the fluorescence lifetime of the europium probe metal as it binds to these substances. A method developed by Horrocks and Sudnick for the determination of the number of water molecules bound to Eu3+ was used to calculate the coordination number of humic-bound Eu3+ from the fluorescence data. The peak shift of the Eu3+ hypersensitive emission band (616 nm) was used to calculate the change in charge of the complex. Equations based on Horrocks and Sudnicks method were also developed to calculate the distribution of metal associated with the different types of binding sites on humic substances by computer modeling of the fluorescence lifetime data.

Sensitive Photothermal Deflection Detector for Microbore Liquid Chromatography

A photothermal deflection detector for microbore liquid chromatography is described. The detection limit of the system under isocratic flow conditions is shown to be 8 × 10−8 absorbance units. This corresponds to 500 fg of analyte (acid sulfonate rug dye) injected on the column. The detection system is shown to be amenable to gradient elution and open tubular chromatography.

A novel approach to metal-humic complexation studies by lanthanide ion probe spectroscopy

Abstract Naturally occurring humic substances are known to be potentially strong binders of metals in the environment. A sensitive spectroscopic technique, based on the unique luminescence properties of the tripositive lanthanide metal ions, has been developed to selectively probe metal binding sites in humic substances. A continuous, multiligand pH dependent ligand model is proposed to describe complexation of metals with humic materials in terms of mean binding strengths, distributions, and concentrations.

Coherent Anti-Stokes Raman Spectroscopy of Polycyclic Aromatic Hydrocarbons

Coherent anti-Stokes Raman spectroscopy (CARS) was used to obtain Raman spectra of thirteen polycyclic aromatic hydrocarbons (PAHs) composed of between three and seven fused rings. The compounds were pumped in the resonance and preresonance regions to obtain the sensitivity necessary for examination at concentrations down to 1.5 × 10 −5 M. A simple mixture of three PAHs was optically separated through the wavelength selectivity of the resonant enhancement process. Comparisons between the spectra of the mixture and the spectrum of each pure component showed essentially no differences when pumped at the same wavelength. Finally, lineshape analysis was performed on the CARS spectra to facilitate comparisons between classes of compounds and for quantitative purposes.

EVALUATION OF AN AUTOMATED HPLC SYSTEM HAVING MULTIPLE DETECTORS

ABSTRACT An automated liquid chromatographic system having multiple detectors has been constructed. The paired-ion separation of six acid sulfonate rug dyes was used to assess the capabilities of the instrumentation. The applicability of the UV/visible multichannel detector is illustrated by visible absorption spectra of the dyes which were taken on the fly. Spectra that provide more specificity were obtained using a coherent anti-Stokes Raman detector. The effects of concentration and pump frequency on spectral profiles in the CARS spectra are shown for a representative dye.

Fourier-Domain Analysis of Complex Line Shapes

The development of a method of phase correction is discussed. Previous phase-correction methods have often required the input of an operator in order to extract phase information from the target spectrum. The use of this Fourier-domain phase-correction technique is discussed specifically in terms of its application to coherent anti-Stokes Raman spectra. The extraction of phase information and subsequent phase correction are discussed.

Coherent Anti-Stokes Raman Spectroscopy of Commercial Oil Samples

Three commercial oil samples were analyzed with the use of the selectivity of resonance CARS. No fractionation procedures were used; the oil samples were simply dissolved in an appropriate solvent and pumped from 365 nm to 480 nm. All three samples could be differentiated by characteristic Raman bands at various pump wavelengths. In addition, comparisons between the CARS spectra of the oil samples and the CARS spectra of pure PAHs at the same pump wavelength yielded tentative identifications of perylene and benzo(ghi)perylene in two of the samples.

A Scanning Algorithm for Condensed-phase CARS and Folded BOXCARS

A scanning algorithm for condensed-phase CARS and folded BOXCARS along with the necessary optical alignment hardware for folded BOXCARS have been developed. Due to the unique geometry of the folded BOXCARS beams, the CARS signal is sufficiently isolated from the pump and Stokes beams such that extended spectra with a lower frequency limit of 70 cm−1 have been obtained.