Kenneth J. Ward

Post-Prandial Blood Glucose Determination by Quantitative Mid-Infrared Spectroscopy

The multivariate calibration method of partial least-squares (PLS) was applied to the mid-infrared spectra of whole blood for quantitatively determining blood glucose concentrations. Separate calibration models were developed on the basis of spectra of whole blood obtained from six diabetic subjects from either in vitro glucose-supplemented blood or blood obtained from the same subjects in the post-prandial state during meal tolerance tests. The cross-validated PLS calibrations yielded average errors in glucose concentration of 11 and 13 mg/dL, respectively. It is desirable to use the calibration models based on the in vitro glucose-supplemented blood for determining glucose concentrations in unknown blood samples. However, when these multivariate calibration models based upon in vitro blood spectra were applied to the spectra of the postprandial blood samples, a subject-dependent concentration bias was observed. The source of this bias was not identified, but when the glucose determinations were corrected for the bias, average concentration errors were found to be 14 mg/dL. Changes in spectrometer design or calibrations based on large numbers of subjects are expected to eliminate the presence of this bias. If these measures do not succeed in eliminating the bias, then methods are demonstrated that significantly reduce the bias while retaining the sensitive outlier detection capabilities of the PLS methods. These latter methods require that the infrared spectrum and reference glucose levels be obtained from a single blood sample from each subject.

Quantitative Infrared Spectroscopy Of Glucose In Blood Using Partial Least-Squares Analyses

The concentration of glucose in drawn samples of human blood has been determined using attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy and partial least-squares (PLS) multivariate calibration. A twelve sample calibration set over the physiological glucose range of 50-400 mg/deciliter (dl) resulted in an average error of 5.24 mg/dl. These results were obtained using cross validated PLS calibration for all data in the frequency range of 950-1200 cm-1. These results are a dramatic improvement relative to those obtained by previous studies of this system using univariate peak height analyses.

Applications Of Image Analysis For Infrared Microspectroscopic Detection Of Contaminants On Microelectronic Devices

The use of infrared microscopy imaging for location and identification of contaminants on microelectronic devices is discussed. Several methods for reconstruction of images from the spectrum acquired at each pixel were compared. Peak-height and peak-integration methods require prior knowledge of the contaminant to narrow the spectral region of interest. These frequency-limited methods performed better than full-spectrum methods. When full-spectrum methods must be used, Gram-Schmidt reconstruction performed better than integration.

Reactivity of Silicates 1. Kinetic Studies of the Hydrolysis of Linear and Cyclic Siloxanes as Models for Defect Structure in Silicates

The kinetics of hydrolysis of hexamethylcyclotrisiloxane and di-t-butyldmesitylcyclodisiloxane in tetrahydrofuran solution have been determined and compared to hydrolysis rates of silica defects. In the presence of sufficient excess water, the first-order rate constant of the cyclotrisiloxane, K = 3.8 x 10/sup -3/ min/sup -1/, of the disappearance of the D2 raman silica defect band it has been proposed to model. Limited hydrolysis rate data for the cyclodisiloxane suggest that it hydrolyzes at least four times faster than the cyclotrisiloxane. These data are consistent with rate data available for silica crack growth and supports the assignment of highly strained siloxane bonds at the crack tip to cyclodisiloxanes. Infrared spectra determined for the cyclodisiloxanes lend further support to this model. 41 refs., 3 figs., 1 tab.

Characterization of surface contaminants using infrared microspectroscopy

Infrared spectroscopy (IR) is a vibrational spectroscopic technique used for the nondestructive identification of molecular species. It provides information about molecular structure by determining the frequency and intensity of light a compound absorbs in the infrared region. The resultant IR absorption spectrum is characteristic of the compound. This spectrum is considered one of the compounds physical properties, like its density or boiling point. However, unlike these other properties only optical isomers have identical infrared absorption spectra. Infrared spectroscopy can be performed on molecular species in any physical state. Therefore, gases, liquids, and solids can all be sampled. Generally, because of the high information content of the infrared spectra of organic molecules IR is most useful for the identification of organic materials. However, many inorganics also exhibit IR detectable molecular vibrations and therefore can be identified by this technique. The paper deals briefly with the use of infrared spectrometers coupled to microscopes, and methods of compressing spectral data by integrating absorbance intensity over a characteristic frequency range.

The Role of Infrared and Raman Microspectroscopies in the Characterization of Particles on Surfaces

The nondestructive identification of particles on surfaces can be accomplished quickly and definitively using vibrational microspectroscopy. Both Fourier-transform infrared (FT-IR) and Raman microspectroscopies are vibrational spectroscopy methods which are now commercially available. These two techniques arfe strongly complementary for several reasons. Both methods detect vibrational energies between atoms in molecules. However, the quantum mechanical selection rules differ such that infrared spectroscopy is more sensitive to asymmetric molecular distortions and Raman spectroscopy to symmetric modes. This means that weak bands in infrared spectra are often strong in Raman spectra and vice versa. Infrared spectroscopy directly measures absorption of incident infrared radiation. However, Raman spectroscopy observes the same vibrational frequencies by measuring the differences in energy between incident and scattered visible light. This means that infrared microspectroscopy has a diffraction limitation of about 10 micrometers while the diffraction limit for Raman microspectroscopy is near 1 micrometer, so Raman microspectroscopy can be used for smaller particles.

Vibrational characteristics and structure of heavy metal fluoride glasses containing thorium and zirconium

This paper reports a vibrational spectroscopic study of a series of glasses composed of Li-Ba-Th-Zr-fluoride in which Th/sup 4 +/ is progressively replaced by Zr/sup 4 +/. In these glasses, Zr/sup 4 +/ shows a more pronounced variation in coordination number than previously observed. Distinct infrared reflectance and polarized Raman bonds due to Th/sup 4 +/ polyhedra are present only in the glasses containing less than 10 mole% ZrF/sub 4/. In the glasses containing 10 or more mole% ZrF/sub 4/, Raman and infrared bands due to Zr/sup 4 +/ polyhedra dominate the vibrational spectra, even in glasses where the ThF/sub 4/ concentration is greater than the ZrF/sub 4/ concentration. The difference in structural behavior or the Th/sup 4 +/ polyhedra as compared to the Zr/sup 4 +/ polyhedra is believed to be due to the smaller electric field intensity of the Th/sup 4 +/ and to the relatively restricted ability of Th/sup 4 +/ to vary its coordination number in response to the availability of F/sup 1 -/.