Alan Howard Ullman

The Herschel-infrared : a useful part of the spectrum

The far-visible (short wave or near, near-infrared or Herschel-infrared) region (∼700–1100 nm) of the electromagnetic spectrum is becoming increasingly popular with spectroscopists, as noted by recent publications and by the inclusion of this region in the coverage range of many more commercial instruments (e.g., NIRSystems, Hewlett-Packard). The region is of particular interest for process analytical chemists, since common visible-region light sources, optics, and detectors may be used, making instrumentation simpler and less expensive than that required for the traditional near- or mid-infrared. This increased simplicity is particularly valuable in process applications because the instruments must operate continuously, 24 hours a day, 365 days a year. In addition, reasonably priced optical fibers, with low light losses, are available for this spectral region, which is not the case yet in the mid-infrared. (This further increases this spectral regions attractiveness for process monitoring applications.) In addition, many of the absorption bands are fairly sharp, so that simple filter photometers may be amenable to process measurements in this region.

Carbon Number Prediction from Herschel-Infrared Spectra Using Partial Least-Squares Regression

In the accompanying note, we pointed out the potential usefulness of the Herschel-infrared (∼700–1100 nm) for solvent measurements, particularly for process measurements over optical fibers and with filter photometers. In this note we demonstrate that multivariate mathematics can be used to extract even more information, which would be difficult or impossible to obtain directly from the spectra. The subtle differences in the spectra of a homologous series of n-alkanes allowed us to use partial least-squares regression (PLS) to model and predict the carbon chain length of the alkanes.

Determination of arsenic in glycerine by hydride generation atomic absorption spectroscopy

A rapid method for the determination of arsenic in glycerine is described. The glycerine sample is diluted and any arsenic present reacted with sodium borohydride and hydrochloric acid to give arsine gas. The evolved arsine is quantitated by atomic absorption spectroscopy in a quartz tube positioned in the flame of a commercial instrument. The method is faster than the colorimetric arsine method recommended by the United States Pharmacopeia and has a precision of 4.4% (RSD) at the 50 µg level (equal to 1.25 µg As/g glycerine).

A capillary gas chromatographic method for the characterization of linear fatty alcohols

A capillary gas chromatography (GC) method for the analysis of fatty alcohols is described. The method can separate fatty alcohols, fatty acids, hydrocarbons and fatty acid methyl esters containing 6 to 22 carbons, as well as fatty-fatty esters to 40 or more carbons. The precision of the method is better than 2% (rsd); accuracy, based on analyses of a standard mixture and a spiking/recovery experiment, is better than 3% (relative difference between known and measured). A calculated hydroxyl value based upon the GC data agrees well with the titrimetric hydroxyl value.

Determination of metals in fatty acid still bottom residues by inductively coupled plasma-atomic emission spectroscopy

Abstract Analysis of fatty acid still bottom residues for major, minor, and trace element content using inductively coupled plasma-atomic emission spectroscopy is described. A combination of isopropyl alcohol and nitric acid (IPA-HNO3) provided the best solvent for the samples. Wavelength selection, ICP operating conditions, detection limits, background equivalent concentrations, and analytical figures of merit were established for the quantitative determination of Zn, Cd, Cu, and Ni. For the determination of trace levels of As, Se, and Hg, direct ICP analysis was found to be too insensitive. Hydride generation for As and Se, and elemental generation of Hg in the plasma were attempted. These elements were not detected in any of the samples.