Physicochemical properties of Ti-grafted SBA-15

Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al₂O₃ catalyst exhibited much better catalytic activity than the Rh-Ni/-Al₂O₃ catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe₃O₄—Cr₂O₃) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date.     

Combining synchronous fluorescence spectroscopy with multivariate methods for the analysis of petrol-kerosene mixtures

Synchronous fluorescence spectroscopy (SFS) is a rapid, sensitive and nondestructive method suitable for the analysis of multifluorophoric mixtures. The present study demonstrates the use of SFS and multivariate methods for the analysis of petroleum products which is a complex mixture of multiple fluorophores. Two multivariate techniques principal component regression (PCR) and partial least square regression (PLSR) have been successfully applied for the classification of petrol-kerosene mixtures. Calibration models were constructed using 35 samples and their validation was carried out with varying composition of petrol and kerosene in the calibration range. The results showed that the method could be used for the estimation of kerosene in kerosene-mixed petrol. The model was found to be sensitive, detecting even 1% contamination of kerosene in petrol.     

Simultaneous spectrophotometric determination of ethinylestradiol and levonorgestrel by partial least squares and principal component regression multivariate calibration

Two spectrophotometric methods for the determination of Ethinylestradiol (ETE) and Levonorgestrel (LEV) by using the multivariate calibration technique of partial least square (PLS) and principal component regression (PCR) are presented. In this study the PLS and PCR are successfully applied to quantify both hormones using the information contained in the absorption spectra of appropriate solutions. In order to do this, a calibration set of standard samples composed of different mixtures of both compounds has been designed. The results found by application of the PLS and PCR methods to the simultaneous determination of mixtures, containing 4–11 μg ml⁻¹ of ETE and 2–23 μg ml⁻¹ of LEV, are reported. Five different oral contraceptives were analyzed and the results were very similar to that obtained by a reference liquid Chromatographic method.     

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) to estimate binding constants of receptors to ligands

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) is used to determine binding constants between vancomycin (Van) from Streptomyces orientalis, teicoplanin (Teic) from Actinoplanes teicomyceticus and ristocetin (Rist) from Nocardia lurida to d-Ala-d-Ala terminus peptides and carbonic anhydrase B (CAB, E.C.4.2.1.1) to arylsulfonamides. Two variations of PFMIACE are described herein. In the first technique, the capillary is partially filled with ligand at increasing concentrations, a non-interacting standard, three or four separate plugs of receptor each separated by small plugs of buffer, a plug containing a second non-interacting standard, and then electrophoresed in buffer. Upon continued electrophoresis, equilibrium is established between the ligand and receptors causing a shift in the migration time of the receptors with respect to the non-interacting standards. This change in migration time is utilized for estimating multiple binding constants (K_b) for the same interaction. In the second technique, separate plugs of sample containing non-interacting standards, peptide one, buffer, and peptide two, were injected into the capillary column. The capillary is partially filled with a series of buffers containing an antibiotic at increasing concentrations and electrophoresed. Peptides migrate through the column at similar electrophoretic mobilities since their charge-to-mass ratios are approximately the same but remain as distinct zones due to the buffer plug between peptides. Upon electrophoresis, the plug of antibiotic flows into the peptide plugs affecting a shift in the migration time of the peptides with respect to the non-interacting standards occurs due to formation of the of the antibiotic-peptide complex. The shift in the migration time of the peptides upon binding to the antibiotic is used for the Scatchard analysis and measurement of a K_b. The PFMIACE technique expands the functionality and potential of ACE as an analytical tool to examine receptor-ligand interactions. In PFMIACE, a smaller amount of sample is required in the assay compared to both conventional ACE and MIACE. Furthermore, a wide array of data is obtained from a single experiment, thus, expediting the assay of biological species.     

Simultaneous Kinetic‐Spectrophotometric Determination of Hydrazine and its Derivatives by Partial Least Squares and Principle Component Regression Methods

Simultaneous kinetic‐spectrophotometric determination of a ternary mixture of hydrazine (HZ) and its derivatives by principal component regression (PCR) and partial least squares (PLS) calibration is described. The methods were based on the difference observed in the reduction rate of iron(III) with HZ, thiosemicarbazide (TSCZ) and phenylhydrazine (PHZ) in the presence of 2,2′‐bipyridine (Bpy). The colored complex of [Fe(Bpy)₃]²⁺ was formed in sodium dodecyl sulfate (SDS) as micellar media, and then monitored at 520 nm. The results showed that simultaneous determination of HZ, TSCZ and PHZ could be performed in their concentration ranges of 1.0–70.0, 0.2–6.0 and 0.1–10.0 μg mL^?1, respectively. The root mean squares errors of prediction (RMSEP) of HZ, TSCZ and PHZ were 0.719, 0.164 and 0.105 (for PLS) 0.788, 0.166 and 0.993 (for PCR), respectively. Both methods (PCR and PLS) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ, TSCZ and PHZ in water samples.     

Multivariate calibration techniques applied to the spectrophotometric analysis of one-to-four component systems

The UV spectrophotometric analysis of a multicomponent mixture containing paracetamol, caffeine, tripelenamine and salicylamide by using multivariate calibration methods, such as principal component regression (PCR) and partial least-squares regression (PLS), was described. The calibration set was based on 47 reference samples, consisting of quaternary, ternary, binary and single-component mixtures, with the aim to develop models able to predict the concentrations of unknown samples containing as many as one-to-four components. The calibration models were optimized by an appropriate selection of the number of factors as well as wavelength ranges to be used for building up the data matrix and excluding any information about the interfering excipients included in pharmaceutics. The PCR and PLS models were compared and their predictive performance was inferred by a successful application to the assays of synthetic mixtures and pharmaceutical formulations.     

Partial-filling affinity capillary electrophoresis

Partial-filling affinity capillary electrophoresis (PFACE) is used to examine the binding interactions between two model biological systems: D-Ala-D-Ala terminus peptides to the glycopeptide antibiotic vancomycin (Van) from Streptomyces orientalis, and arylsulfonamides to carbonic anhydrase B (CAB, EC 4.2.1.1, bovine erythrocytes). Using these two systems, modifications in the PFACE technique are demonstrated including flow-through PFACE (FTPFACE), competitive flow-through PFACE (CFTPFACE), on-column ligand synthesis PFACE (OCLSPFACE), and multiple-step ligand injection PFACE (MSLIPFACE). In PFACE small plugs of sample are injected into the capillary column and an equilibrium is established between receptor and ligand during electrophoresis. Binding constants are then obtained by Scatchard analysis using changes in the migration time of the receptor/ligand on changing the concentration of the ligand/receptor. Data demonstrating the quantitative potential of these methods are presented. This review focuses on the unique capabilities of the different PFACE techniques as applied to two model biological systems.     

Partial molar volumes of amino acid derivatives in water

The partial molar volumes at infinite dilution for a number of hydrochlorides and sodium salts of N-methyl derivatives of , -aminocarboxylic acids in water at 25°C are measured and related to their van der Waals volumes. Results indicate that 4.96±0.48 water molecules hydrate a betaine hydrochloride. Volumes of proton ionization and interaction terms are evaluated. Group contributions to the partial molar volumes are also reported.     

Volumetric properties of the water + ethylenediamine mixture at atmospheric pressure from 288.15 to 353.15 K

Densities of the water + ethylenediamine binary system were measured at atmospheric pressure over the whole range of compositions at temperatures from 288.15 to 353.15 K using an Anton Paar digital vibrating glass tube densimeter. Density increases with water content. The experimental excess molar volume data have been correlated with the Redlich-Kister equation, and partial molar volumes calculated at infinite dilution for each component.     

Simultaneous kinetic spectrophotometric determination of cyanide and thiocyanate using the partial least squares (PLS) regression

The partial least squares (PLS-1) calibration model based on spectrophotometric measurement, for the simultaneous determination of CN⁻ and SCN⁻ ions is described. The method is based on the difference in the rate of the reaction between CN⁻ and SCN⁻ ions with chloramine-T in a pH 4.0 buffer solution and at 30 °C. The produced cyanogen chloride (CNCl) reacts with pyridine and the product condenses with barbituric acid and forms a final colored product. The absorption kinetic profiles of the solutions were monitored by measuring absorbance at 578 nm in the time range 20-180 s after initiation of the reaction with 2 s intervals. The experimental calibration matrix for partial least squares (PLS-1) calibration was designed with 31 samples. The cross-validation method was used for selecting the number of factors. The results showed that simultaneous determination could be performed in the range 10.0-900.0 and 50.0-1200.0 ng mL⁻¹ for CN⁻ and SCN⁻ ions, respectively. The proposed method was successfully applied to the simultaneous determination of cyanide and thiocyanate in water samples.