Temperature, pressure, viscosity, and other process variables fluctuate during an industrial process. When vibrational spectra are measured on- or in-line for process analytical and control purposes, the fluctuations influence the shape of the spectra in a nonlinear manner. The influence of these temperature-induced spectral variations on the predictive ability of multivariate calibration model is assessed. Short-wave NIR spectra of ethanol/water/2-propanol mixtures are taken at different temperatures, and different local and global partial least-squares calibration strategies are applied. The resulting prediction errors and sensitivity vectors of a test set are compared. For data with no temperature variation, the local models perform best with high sensitivity but the knowledge of the temperature for prediction measurements cannot aid in the improvement of local model predictions when temperature variation is introduced. The prediction errors of global models are considerably lower when temperature variation is present in the data set but at the expense of sensitivity. To be able to build temperature-stable calibration models with high sensitivity, a way of explicitly modeling the temperature should be found.

Methacrylate ester-based monolithic stationary phases were prepared in situ in fused-silica capillaries and simultaneously in vials. The influence of the composition of the polymerization mixture on the morphology was studied with mercury intrusion porosimetry, scanning electron microscopy, and nitrogen adsorption measurements. A high-density porous polymeric material with a unimodal pore-size distribution was prepared with 40 wt % monomers and 60 wt % solvent in the mixture. A low-density material, prepared with a 20:80 ratio of monomers versus pore-forming solvent, showed a bimodal pore-size distribution and a much finer structure than the high-density monolith. The characteristic pore size could be controlled by changing the ratio of pore-forming solvents. With increasing solvent polarity, both the pore size and the dimension of the globules increased. The best efficiency in the CEC mode was obtained with an average pore size of 600 nm. Low-density monoliths exhibited lower A- and C-terms than high-density monoliths. With the optimal monolithic material, a minimum plate height of 5 mum could be obtained. The low-density monolith also performed better in the HPLC mode, giving a minimum plate height of 15 mum and a much higher flow permeability than that of the high-density material.

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