L. V. Azarraga

Gold Coating of Glass Tubes for Gas Chromatography/Fourier Transform Infrared Spectroscopy “Light-Pipe” Gas Cells

The sensitivity of gas chromatography/Fourier transform infrared spectroscopy (GC/FT-IR) may be significantly improved by use of small bore gold-coated glass gas cells. This note describes the method of preparing internally gold-coated glass or quartz tubes for GC-IR applications.

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.

Fourier Encoded Data Searching of Infrared Spectra (FEDS/IRS)

A new library searching technique is reported that relies on Fourier transforms of infrared (IR) absorbance spectra. Searching in the time domain is shown to be more tolerant to noise than searches in the spectral domain and fewer points are required to encode the unique characteristics of the individual spectrum. This decreases both search time and library storage requirements. Additionally, time-domain classification of IR spectra is demonstrated and the possibility of indexing the library for a binary search is discussed.

Computer-Controlled Absorption, Fluorescence, and Coherent Anti-Stokes Raman Spectrometry for Liquid Chromatographic Detection:

A computer-controlled liquid chromatograph is described using two pumps for gradient elution. An absorption, fluorescence, and fluorescence-excitation detection system is centered around a silicon intensified target Vidicon detector. This allows fluorescence and absorption spectra to be recorded and stored every 3 s without stopping flow. A coherent anti-Stokes Raman spectrometer is also used in series in the detection scheme. This overall system allows great flexibility and the acquisition of a large amount of data from a single separation.

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.

Initial Results From An Interferogram-Based Search System

Search algorithms based on the time (or distance) domain representation of the infrared absorption spectrum were constructed and demonstrated. Preliminary results indicate significant advantages in speed, reliability, and efficiency of the search systems over the traditional spectrum-based method. A direct interferogram-based search system with a high degree of reliability was demonstrated for the first time and the requirements for an instrument-independent data were delineated.