Biomedical subjects

Josef Diewok

Publications and source records attributed to Josef Diewok.

3 recordsLinked to original sources

PubMed2003

High-performance liquid chromatography with diamond ATR-FTIR detection for the determination of carbohydrates, alcohols and organic acids in red wine.

A horizontal diamond attenuated total reflection (ATR) element has been incorporated in a flow-through cell with low dead volume and used for on-line mid-IR detection in high-performance liquid chromatography. The chemical inertness of the ATR element permitted the use of a strongly acidic mobile phase in the isocratic separation. The hyphenation was used for the analysis of organic acids, sugars and alcohols in red wine. In the case of co-eluting analytes multivariate curve resolution-alternating least squares (MCR-ALS) was successfully employed for quantitative analysis.

Alcohols↗

PubMed2003

Application of a combination of hard and soft modeling for equilibrium systems to the quantitative analysis of pH-modulated mixture samples.

pH modulation of aqueous mixture samples combined with FT-IR detection and a powerful second-order resolution method is proposed for both resolution and quantitation of acid analytes in the presence of similarly behaving interferences. The proposed method allows for the analyte determination in mixtures using a single standard sample per analyte. Due to the very similar pKa values of the investigated analytes and interferences, the highly correlated concentration profiles of these compounds cannot be successfully resolved with pure soft-modeling second-order approaches. The inclusion of a hard-modeling constraint based on the acid-base equilibrium model in the soft-modeling curve resolution method has allowed for the unambiguous resolution of the analyte profiles and, as a consequence, for the correct quantitation of this compound in the mixture sample. A detailed discussion of the combined hard-soft-modeling approach as well as the analytical problem and the quantitation results is given. Also, strategies to overcome problems associated with variation in pKa values between different samples are addressed. Due to the flexible implementation of the hard-model equilibrium constraint in the multivariate curve resolution-alternating least squares method, this approach is expected to be useful also for analysis of other complex mixed equilibrium-based chemical systems.

Journal Article↗

PubMed2002

2D correlation spectroscopy and multivariate curve resolution in analyzing pH-dependent evolving systems monitored by FT-IR spectroscopy, a comparative study.

Multivariate curve resolution (MCR) and 2D correlation spectroscopy (2D-CoS), including sample-sample correlation, have been applied to the analysis of evolving midinfrared spectroscopic data sets obtained from titrations of organic acids in aqueous solution. In these data sets, well-defined species with significant differences in their spectra are responsible for the spectral variation observed. The two fundamentally different chemometric techniques have been evaluated and discussed on the basis of experimental and supportive simulated data sets. MCR gives information that can be directly related to the chemical species that is of importance from a practical point of view, whereas 2D-CoS results normally require more interpretation. The obtained conclusions are regarded valid for similar evolving data, which are increasingly being encountered in analytical chemistry when multivariate detectors are used to follow dynamic processes, including separations as well as chemical reactions, among others.

Journal Article↗