Fourier transform infrared analysis (FTIR) was used in combination with partial least squares regression (PLS) to predict the concentration of acetone in milk. FTIR spectra were compared with results of a gas-chromatographic head space method. Principal component analysis of whole spectra (3000 to 1000 cm(-1)) suggested to reduce the spectrum of analysis for acetone to 1450 to 1200 cm(-1). A second derivative was applied to the spectra to remove baseline effects and further enhance the spectral features. Full cross-validation was used to compare the reference with predicted acetone concentrations of samples not included in model development. PLS applied to the full spectral range resulted in a complex 19-factor model with a cross-validation error of 0.22 mM. After reducing the spectrum and taking the second derivative, we obtained a model with seven factors that yielded a cross-validation error of 0.21 mM. This compares favorably with a previously reported model with 20 factors and an error of 0.25 mM. Using PLS predictions to identify cows with subclinical ketosis resulted in 95 to 100% sensitivity and 96 to 100% specificity when the threshold for subclinical ketosis was 0.4 to 1.0 mM. The corresponding positive predictive values were > or = 76% and the negative predictive values > 98% throughout an assumed range of subclinical ketosis prevalence of 10 to 30%.

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The structure and binding properties of a series of receptor molecules based on the building block diphenylglycoluril are described. These receptors bind dihydroxy-substituted aromatic guests in chloroform solution by means of hydrogen bonding and tt-tt stacking interactions. IR difference spectroscopy shows that the hydrogen bonds are formed between the OH groups of the guest molecule and the 7r-electrons of the urea carbonyl groups present in the receptor. The structure of the complexes was further investigated by comparing the complexation-induced shifts in the 'H N M R spectra with the calculated shifts for a number of geometries of the host-guest complexes. These data demonstrate that the guest molecules are clamped within the cavity of the receptor.

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Al&act-Infrareddata have been recorded of the hydroxyl stretching band for about 70 monohydrie saturated alcohols in dilute carbon tetrachloride solution. The wavenumber maximum, the half-bsndwidth and the band pattern could be related to the stru&ure of the molecules. Not only primary, secondary and tertiary alcohols cau be distinguished but also @-branched and cyolic ones. Four effects seem to be connected with the OH stretching band; viz. substitution and Gxation both lowering the frequency, and rotation and shielding both enhancing it. For identification purposes a table correlating structure, wavenumber and half-bandwidth is presented.