The use of information theory for evaluating the quality of thin-layer chromatographic separations

Infrared Spectroscopy and Chemometric Applications for the Qualitative and Quantitative Investigation of Grapevine Organs

The fourth agricultural revolution is leading us into a time of using data science as a tool to implement precision viticulture. Infrared spectroscopy provides the means for rapid and large-scale data collection to achieve this goal. The non-invasive applications of infrared spectroscopy in grapevines are still in its infancy, but recent studies have reported its feasibility. This review examines near infrared and mid infrared spectroscopy for the qualitative and quantitative investigation of intact grapevine organs. Qualitative applications, with the focus on using spectral data for categorization purposes, is discussed. The quantitative applications discussed in this review focuses on the methods associated with carbohydrates, nitrogen, and amino acids, using both invasive and non-invasive means of sample measurement. Few studies have investigated the use of infrared spectroscopy for the direct measurement of intact, fresh, and unfrozen grapevine organs such as berries or leaves, and these studies are examined in depth. The chemometric procedures associated with qualitative and quantitative infrared techniques are discussed, followed by the critical evaluation of the future prospects that could be expected in the field.

Multivariate Analysis Applications in X-ray Diffraction

Multivariate analysis (MA) is becoming a fundamental tool for processing in an efficient way the large amount of data collected in X-ray diffraction experiments. Multi-wedge data collections can increase the data quality in case of tiny protein crystals; in situ or operando setups allow investigating changes on powder samples occurring during repeated fast measurements; pump and probe experiments at X-ray free-electron laser (XFEL) sources supply structural characterization of fast photo-excitation processes. In all these cases, MA can facilitate the extraction of relevant information hidden in data, disclosing the possibility of automatic data processing even in absence of a priori structural knowledge. MA methods recently used in the field of X-ray diffraction are here reviewed and described, giving hints about theoretical background and possible applications. The use of MA in the framework of the modulated enhanced diffraction technique is described in detail.

Separation of N-alkyl phenothiazine sulfones by HPTLC using an optimum mobile phase

In high performance thin layer chromatography some form of optimization is necessary if complete separation of all components is required. The selection of mobile phase composition is one of the most important components of an optimization strategies. The aim of this paper is the separation of the N-alkyl phenothiazine sulfones by high performance thin layer chromatography using an optimum mobile phase system. The optimum composition of mobile phase (toluene-ethyl ether-chloroform, 30:50:20, v/v) are given by the maximum of objective function (F(obj)=10.6110).

Application of numerical taxonomy techniques to the choice of optimum mobile phase in high-performance thin-layer chromatography (HPTLC)

A total of eight solvent systems used for the separation of 1,4-benzodiazepine mixtures were investigated. The classification of solvent systems was carried out by the numerical taxonomy technique. The selection of optimum solvent system was accomplished on the basis of information quantity and objective function. The method was found to be a rapid and efficient tool in the choice of optimum system solvent.

Drug screening in biological fluids. The need for a systematic approach

In this paper the key steps towards drug screening in biological fluids are considered: (i) sample work up-isolation-concentration; (ii) differentiation-detection; (iii) identification. For (i) solid-phase extraction has very good potential; for (ii) thin-layer chromatography, gas chromatography and high-performance liquid chromatography, in combination with their respective detection modes, each have their particular advantages and disadvantages; for (iii) extensive computerized data bases are essential. It is emphasized that each step must be approached and carried out in a systematic way, not only to make sure that all substances of interest can be detected, but also for their correct identification. To this end all analytical procedures and techniques used require extensive validation of their detection and identification properties.

Qualitative organic analysis. I. Identification of drugs by principal components analysis of standardized thin-layer chromatographic data in four eluent systems

Principal component analysis of standardized RF values in four eluent systems [ethyl acetate-methanol-30% ammonia (85:10:15), cyclohexane-toluene-diethylamine (65:25:10), ethyl acetate-chloroform (50:50) and acetone, with the plate dipped in potassium hydroxide solution] provided a two-component model which accounts for 73% of the total variance. The "scores" plot allowed the restriction of the range of inquiry to a few candidates. This result is of great practical significance in analytical toxicology, especially when account is taken of the cost, the time, the analytical instrumentation and the simplicity of the calculations required by the method.

Chromatography in analytical toxicology — state of the art and future perspectives

The aims of systematic toxicological analysis are considered with respect to the principal techniques available for quantitative and qualitative purposes. The use of thin-layer (TLC), gas-liquid (GLC), capillary GLC and high-performance liquid chromatography (HPLC) is discussed, with special reference to the need for standardized systems for toxicological analysis. The selectivity of correlations presented as mean list length values, derived from archives of Kováts retention indices in GLC and of Rf-values in up to eight TLC systems, is illustrated by some typical examples. The dependence of Kováts retention indices on column packing materials and on load capacity in CGLC is discussed and the particular difficulties of comparable standard systems in HPLC are considered. Conclusions are drawn concerning the established 'workhorse' techniques, such as TLC and GLC. The need to adapt and standardize other powerful analytical methods, such as HPLC, MS and GLC-MS, is examined with regard to the requirements of toxicological analysis.

Development of a standardized analysis strategy for basic drugs, using ion-pair extraction and high-performance liquid chromatography — II. Selection of preferred HPLC-systems

A test set of 100 basic drugs has been chromatographed on 16 preselected HPLC-systems using four different types of stationary phase (Si-, NH2-, CN- and C18-). A numerical treatment of the chromatographic data, based on the discriminating power concept, results in the selection of two preferred HPLC systems for basic drugs. both using the CN-bonded phase. The preferred eluents are n-heptane-dichloromethane-acetonitrile-propylamine (25:50:25:0.1) and acetonitrile-water-propylamine (90:10: 0.01). The two preferred HPLC systems are adopted in a standardized analysis strategy.

Evaluation of weighted discriminating power calculations as an aid to the selection of chromatographic systems for the analyses of drugs

In toxicological analyses some chromatographic separations are more important than others. Two weighting methods for chromatographic data are described which incorporate the importance of particular separations into discriminating power calculations. The data were abstracted from a publication on the separations of acidic drugs on thin-layer chromatographic systems. When compared with non-weighted discriminating power calculations, those obtained with the weighting procedure did not give any advantage.

Choice of thin-layer chromatographic systems for the routine screening for acidic drugs during toxicological analyses

The efficiencies of fifteen thin-layer silica gel chromatographic systems in separating commonly encountered acidic drugs are compared. The discriminating powers of the systems are measured both individually and in combination. Ethyl acetate and chloroform-methanol (9:1) are found to be the two best systems. The combination of the ethyl acetate-methanol-ammonia (85:10:5) system with either of these gives the best pair of systems. Various sequences of spray reagents are also examined.

Evaluation and optimal combination of TLC systems for qualitative identification I: sulfonamides

A mathematical criterion for the evaluation of chromatographic analysis procedures is given by the information content as derived from Shannon's equation. This information content yields a numerical value representative of the merits of each chromatographic separation and thus allows selection of the optimal systems. In most cases, however, one analysis is not sufficient to allow the qualitative identification of the sample. Therefore, several chromatographic systems are combined. Two approaches allow the desired combination; one either calculates the information content of several procedures as one mathematical value or classifies the systems according to mutual resemblance by numerical taxonomy techniques. From the resulting groups of dissimilar systems, one optimal system can be chosen per group according to the information content. The results obtained by these mathematical procedures are illustrated with a practical example: the selection and evaluation of systems for the TLC analysis of sulfonamides.

Evaluation and selection of optimal solvents and solvent combinations in thin-layer chromatography. Application of the method to basic drugs

A series of simple mathematical techniques for the evaluation of solvents and solvent combinations in thin-layer chromatography have been investigated. A strategy for the rapid selection of the optimum combination is proposed. It uses classification procedures based on calculation of the similarity between systems. The classification is carried out using a simple graph-theoretical procedure (Kruskal's algorithm) or numerical taxonomy. The selection of optimal sets from the clusters which appear in the classification is based on the information content as derived from Shannon's equation. The method has been applied to an RF data set for basic drugs. It is concluded that these methods indeed allow the selection of optimal systems or combination of systems.