Analytical approaches to expanding the use of capillary electrophoresis in routine food analysis

Capillary Electrophoresis (CE) is becoming an ever more powerful analytical technique for the separation, identification, and quantification of a wide variety of compounds of interest in many application fields. Particularly in food analysis this technique can offer interesting advantages over chromatographic techniques because of its greater simplicity and efficiency. Nevertheless, CE needs to advance with regard to compatibility with sample matrices, sensitivity, and robustness of the methodologies in order to gain even wider acceptance in food analysis laboratories, specially for routine work. This article presents various approaches to expanding the analytical usefulness of CE in food analysis, discussing their advantages over conventional CE. These approaches focus on sample screening, automated sample preparation with on-line CE arrangements, and the automatic integration of calibration in routine analytical work with CE.     

Micellar electrokinetic capillary chromatography for the determination of Viagra and its metabolite (UK-103,320) in human serum

Micellar electrokinetic capillary chromatography (MEKC) was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320) in human serum in a concentration range of clinical interest. For MEKC, human serum samples spiked with SC and UK were obtained directly after elution with methanol from a tC18 cartridge. The extract was evaporated and regenerated in a solution 1 mM of phosphate buffer (pH 12.3) which contained a methanol percentage of 20% that was analyzed using phosphate buffer (pH 12.3, 10 mM) containing 30 mM sodium dodecyl sulfate (SDS) as separation electrolyte and a fused-silica capillary. This method gave satisfactory interday precision with respect to migration times relative standard deviation (RSD < 1%) and linear responses for the concentration ranges investigated (0.50-3.50 mg L(-1) for the compound SC and 0.90-4.60 mg L(-1) for UK). An intraday RSD (n = 5 graphs) between the slopes of the calibration graphs was acceptable (6.40%) for SC and (3.37%) for UK. A satisfactory interday precision between slopes was also obtained (RSD 4.10% for SC and a RSD 2.72% for UK) which demonstrated the ruggedness of this method. Detection limits (S/N = 3) were about 200 ng/mL for both compounds in human serum. MEKC was shown as a good method with regards to simplicity, precision and sensitivity.     

Determination of Clobazam, Clorazepate, Flurazepam and Flunitrazepam in pharmaceutical preparations

The separation of four benzodiazepines (Flurazepam, Flunitrazepam, Clobazam and Clorazepate) in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. It was carried out at 25 degrees C and 25 kV by using a 57 cm (50 cm to the detector)x75 mum i.d. fused silica capillary and a 15 mM borate buffer (pH 9.2), 35 mM sodium dodecylsulfate (SDS) and 35 mM sodium deoxycholate water solution. Under these conditions, the analysis was performed in 8 min with acceptable limits of quantification (between 3 and 5 mg l(-1)). The method has been applied for quantifying these benzodiazepines in serum and different commercial formulations with recoveries near 100%.     

Natural spline functions,their associated eigenvalue problem

Summary We consider the problem of studying the behaviour of the eigenvalues associated with spline functions with equally spaced knots. We show that they are wherem is the order of the spline andn, the number of knots.This result is of particular interest to prove optimality properties of the Generalized Cross-Validation Method and had been conjectured by Craven and Wahba in a recent paper.     

Pyrrolodiazines. 2. Structure and Chemistry of Pyrrolo[1,2-a]pyrazine and 1,3-Dipolar Cycloaddition of Its Azomethine Ylides

A new synthesis of the pyrrolo[1,2-a]pyrazine system from pyrrole is described. In light of the ab initio calculations carried out on this heterocyclic system some of its basic chemistry was investigated and included electrophilic substitution, addition of organolithium reagents, metalation with lithium diisopropylamide and subsequent reaction with electrophiles, and formation of salts by quaternization of the nonbridgehead nitrogen. N-ylides obtained from these salts undergo 1,3-dipolar cycloaddition with suitable dipolarophiles to give dipyrrolo[1,2-a]pyrazines, pyrazolo[1,5-a]-pyrrolo[2,1-c]pyrazines, and heterobetaines. Examples of intramolecular 1,3-dipolar cycloadditions are also reported.     

Aromaticity of annulenes and annulene ions with 4v+2 electrons from the viewpoint of the theory of Hartree-Fock instabilities

The connection between the aromaticity of annulenes and annulene ions with 4v+2 -electrons and the stability of the closed-shell restricted Hartree-Fock (RHF) solutions for these systems is discussed in the framework of the PPP-approximation. It is shown that the tendency towards an uniform electron density distribution in aromatic cycles is paralleled by the stability properties of the corresponding closed-shell RHF solutions. The stability investigations are demonstrated to provide realistic estimates of the critical ring sizes at which Hückel's 4v+2 rule breaks down.     

Multi-scale homogenization-based modeling of semi-crystalline polymers

This paper presents a finite-strain, multi-scale constitutive model for semi-crystalline polymers, accounting explicitly for the current state and evolution of the underlying crystallographic, lamellar and morphological texture. Specifically, a semi-crystalline polymer is modeled as a two-scale composite, assumed to be, at the larger length scale, an aggregate of randomly distributed grains that, at the smaller length scale, are made up of alternating layers of an amorphous and a crystalline phase. The model incorporates finite elasticity for the amorphous phase and crystallographic hardening for the crystalline phase. The instantaneous effective response of this composite is determined by means of multi-scale homogenization methods, consisting in the use of a “linear comparison composite” (LCC) with the same internal structure as the actual nonlinear composite, with local properties that are optimally chosen via suitably designed variational principles. The effective properties of the resulting two-scale LCC are obtained through a “sequential” homogenization procedure, involving the exact solution for the effective behavior of the lamellar grains and a self-consistent estimate for the aggregate. The latter results are also used to establish evolution laws for the appropriate internal variables in the material. The predictions of the model for the macroscopic response and texture evolution in high-density polyethylene are confronted with available experimental results and compared with those of earlier models.     

A study of the Immune Epitope Database for some fungi species using network topological indices

In the last years, the encryption of system structure information with different network topological indices has been a very active field of research. In the present study, we assembled for the first time a complex network using data obtained from the Immune Epitope Database for fungi species, and we then considered the general topology, the node degree distribution, and the local structure of this network. We also calculated eight node centrality measures for the observed network and compared it with three theoretical models. In view of the results obtained, we may expect that the present approach can become a valuable tool to explore the complexity of this database, as well as for the storage, manipulation, comparison, and retrieval of information contained therein.