Chiral separations of polar compounds by hydrophilic interaction chromatography with evaporative light scattering detection.

The chiral separations of drug substances and underivatized amino acids were demonstrated in this study through the use of hydrophilic interaction chromatography (HILIC). The polar character of the model compounds presented challenges for their analysis by traditional modes of chromatography, but through the employment of multimodal chromatography utilizing the HILIC mechanism and cyclodextrin- or teicoplanin-derivatized stationary phases, effective resolution was achieved. The analytes lacked sufficient ultraviolet chromophores, requiring their determination by evaporative light scattering detection. HILIC was demonstrated to represent a novel technique for the facilitation of chiral chromatography by providing an environment of solubility and retention that could not be achieved through the use of the traditional methods of reversed-phase, normal-phase, or polar organic mode.

Enantiomeric separations of dansyl amino acids using the macrocyclic antibiotic A35512B as a chiral selector in capillary electrophoresis.

The macrocyclic antibiotic A35512B was examined as a chiral selector for capillary electrophoresis (CE) using thirteen racemic dansyl amino acids as test analytes. The chiral selectivity of A35512B was evaluated as a function of the run buffer pH, antibiotic concentration, and organic modifier composition. After optimizing these parameters, the macrocylic antibiotic A35512B provided high resolutions of all the enantiomers for the thirteen dansyl amino acids tested in this study.

Evaluation of the macrocyclic antibiotic LY333328 as a chiral selector when used as a mobile phase additive in narrow bore HPLC.

The macrocyclic antibiotic LY333328 has been evaluated as a chiral selector for the enantioseparation of nine dansylated amino acids. This macrocyclic glycopeptide was used as a chiral mobile phase additive (CMPA) in conjunction with narrow bore high-performance liquid chromatography (HPLC). The key mobile phase parameters of LY333328 concentration and buffer pH were varied, along with variations in stationary phases consisting of C8, phenyl, cyano, and silica. After observing and plotting changes in retention and resolution based on corresponding variation in these parameters, a better understanding of the behavior of this chiral selector was obtained. The pKa values of the dansyl amino acid analytes and LY333328 were measured and used to gain a better understanding of the microenvironment in which these enantioseparations occur. Optimized conditions resulted in the baseline separation of eight of nine dansyl amino acids.

Statistical method for quantifying mobile phase selectivity in one- and two-dimensional overpressured layer chromatography.

A method for selecting mobile phases for either one-dimensional (1-D) or two-dimensional (2-D) planar chromatography is described and is applied to the separation of steroids by overpressured layer chromatography [Formula: see text] a form of forced-flow thin-layer chromatography [Formula: see text] using both normal- and reversed-phase chromatography. Two metrics are used for evaluating the separation quality of simulated chromatograms for each of 100 (or more) subsets of a set of 30 steroids in each of 15 1-D, and 105 2-D systems. The subsets vary in size between five and 25 steroids. Butyl acetate/toluene on silica gel and aqueous 2,2,2-trifluoroethanol are, on average, the highest and second highest ranked 1-D systems, respectively, for separating all subset sizes. These two systems are the constituent members of the system that is, on average, the highest ranked 2-D system for all subset sizes. The probability of the above systems being highest ranked decreases with decreasing subset size. There is only a 17% probability of butyl acetate/toluene on silica being the best system for separating a subset of five steroids, while there is a 3% probability of this being the worst system for this subset size. The spot capacity of each system can be estimated by considering 100 subsets of each size and noting the largest subset size that yields an acceptable value of one of the metrics used for measuring separation quality. The mobile phase selectivity may be quantified using the actual values of either of the two separation metrics, or by a nonparametric approach. The latter is used in such a way that a difference of unity in the ranking (for a given subset size) of two systems corresponds to a 95% probability that the higher ranked system will yield the better separation.

Stability of fluoxetine hydrochloride in fluoxetine solution diluted with common pharmaceutical diluents.

The stability of fluoxetine hydrochloride in fluoxetine solution diluted with five common pharmaceutical diluents was studied. Fluoxetine syrup, containing fluoxetine 4 mg/mL (as the hydrochloride salt), was diluted to 1 and 2 mg/mL in each of the following: deionized water; Simple Syrup, British Pharmacopeia; Simple Syrup, USP; Aromatic Elixir, USP; and grape-cranberry drink. Each solution was divided into eight 120-mL amber glass bottles: four stored at 5 degrees C and four stored at 30 degrees C. Samples were removed from each bottle at time zero and two, four, and eight weeks and assayed in triplicate with high-performance liquid chromatographic methods for determining fluoxetine concentration and concentration of its primary degradation product, alpha-[2-(methylamino)ethyl]benzene methanol. Stability was established if the fluoxetine concentration changed by < 10% and if the concentration of the degradation product was < 1% of the initial fluoxetine concentration. No test mixture dropped below 95% of the initial fluoxetine concentration or exceeded 0.5% degradation product during the study period. Fluoxetine hydrochloride was stable for eight weeks in fluoxetine solution diluted to 1 or 2 mg/mL with common pharmaceutical diluents and stored at 5 or 30 degrees C.

The significance of the concordance rate for type 1 (insulin-dependent) diabetes in identical twins.

We studied prospectively 49 non-diabetic identical twins of recently-diagnosed Type 1 (insulin-dependent) diabetic patients for up to 24 years (median 9 years). During this time 15 developed Type 1 diabetes. Actuarial analysis indicates that by 12 years 34% of the twins will have developed Type 1 diabetes and that thereafter only another 2% will do so. Inevitable bias in ascertainment of the twins makes it likely that the true figure is less. We conclude that factors which are not genetically determined must be important in the pathogenesis of the disease. The rates of developing Type 1 diabetes in the co-twins declines sharply in the years after diagnosis of the index twin, which suggests that the initiation of the process leading to Type 1 diabetes occurs within a finite, and not a prolonged, period.

Blood sampling techniques in reptiles.

Disposition of the superficial blood vessels was studied in 38 species of reptiles with a view to examining their suitability for taking blood samples. It was concluded that the coccygeal veins were probably the most suitable for this purpose and the precise techniques for sampling from the different orders are described.