Spectrophotometric Determination of Phenytoin Sodium in Pure and Pharmaceutical Preparations

 Phenytoin sodium reacts with o-nitrobenzoic acid in alkaline media after heating for 10 minutes at 70 °C, to give a red coloured complex having maximum absorbance at 510 nm. The reaction is selective for phenytoin sodium with 0.01 mg/10 mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.01 mg to 3 mg/10 mL of phenytoin sodium and the relative standard deviation is 0.29%. The quantitative assessment of tolerable amounts of other drugs is also studied. Received May 2, 2000. Revision May 11, 2001.     

Seleno-β-lactams: synthesis of monocyclic and spirocyclic selenoazetidin-2-ones

An efficient protocol for the synthesis of novel seleno-β-lactams using operationally simple strategies is presented. 3-Phenyl/benzylseleno-β-lactams, obtained from 2-phenyl/benzylselenoethanoic acids, are transformed to cis-3-chloro-3-phenyl/benzylseleno-β-lactams, which undergo reaction with various active aliphatic and aromatic substrates catalyzed by Lewis acid to produce cis-3-alkoxy-3-phenyl/benzylseleno-β-lactams and C-3 monosubstituted seleno-β-lactams. Halogen mediated intraselenyl cyclization of cis-3-(prop-2-ynyloxy)-3-benzylseleno-β-lactams affords novel spiro seleno-β-lactams.     

Quantification of risperidone and 9-hydroxyrisperidone in plasma and saliva from adult and pediatric patients by liquid chromatography-mass spectrometry

A robust and validated LC-MS-MS quantitative method, using column switching and mutiple reaction monitoring was developed for the analysis of risperidone (RIS) and 9-hydroxyrisperidone in human plasma and saliva. The analytical range was 1-100 ng/ml. The method used 25 microl of sample precipitated with 75 microl of acetonitrile containing internal standard (R068808). Analyses were conducted on a PE Sciex API-III + triple quadrupole mass spectrometer fitted with a Turbo IonSpray source. The method was validated for human plasma using EDTA as the anticoagulant and cross-validated to heparinized human plasma and saliva. The recoveries of risperidone and 9-hydroxyrisperidone were 90-93 and 89-93%, respectively. The validated method was applied to clinical samples to study risperidone and 9-hydroxyrisperidone concentrations in plasma and saliva. Risperidone and 9-hydroxyrisperidone appear in the saliva of patients treated with risperidone. Their detection/quantification in saliva provides evidence for recent adherence with therapy.     

Isolation of carotenoids from plant materials and dietary supplements by high-speed counter-current chromatography

Methods for the isolation of lipophilic pigments from crude extracts of plant materials (spinach and sweet corn) by high-speed counter-current chromatography (HSCCC) were developed. Particular attention was given to (all-E)-lutein and (all-E)-zeaxanthin. However, the concomitant pigments neoxanthin, violaxanthin and beta-carotene as well as chlorophylls a and b were also considered. Furthermore, for the first time dietary supplements containing lutein and zeaxanthin were also used as a source for the recovery of carotenoids. Due to their simple matrix (oily excipient in soft gelatine capsules), sample preparation was facilitated and consumption of solvents was minimized. The carotenoids were characterized by 1H NMR spectroscopy, by LC/APcI-MS in the positive ionization mode, and by UV-vis spectroscopy.Data showed that the target compounds were of high purity (90 - 93%). Lutein and zeaxanthin may be used as reference substances for analytical purposes.     

Spectrophotometric determination of some antipsychotic phenothiazines

Thioridazine hydrochloride reacts with sodium nitrite and antimony(III) potassium tartrate in the presence of hydrogen peroxide to give a yellowish orange colour having maximum absorbance at 420 nm. The reaction is specific for antipsychotic phenothiazines with 1 g/ml as visual limit of identification and provides a basis for a new Spectrophotometric determination. The colour reaction obeys Beer's Law from 0.01 to 1.25 mg/10ml thioridazine. The standard deviation does not exceed 0.050 mg/10 ml. The method is successfully applied to pure and pharmaceutical preparations of antipsychotic phenothiazines, as well as to urine samples. The quantitative assessment of tolerable amounts of other drugs is also studied.     

Asymptotic distribution of the OLS estimator for a purely autoregressive spatial model

We derive the asymptotics of the OLS estimator for a purely autoregressive spatial model. Only low-level conditions are used. As the sample size increases, the spatial matrix is assumed to approach a square-integrable function on the square (0,1)². The asymptotic distribution is a ratio of two infinite linear combinations of χ² variables. The formula involves eigenvalues of an integral operator associated with the function approached by the spatial matrices. Under the conditions imposed identification conditions for the maximum likelihood method and method of moments fail. A corrective two-step procedure using the OLS estimator is proposed.     

Fabric phase sorptive extraction/GC‐MS method for rapid determination of broad polarity spectrum multi‐class emerging pollutants in various aqueous samples

A rapid extraction and cleanup method using selective fabric phase sorptive extraction combined with gas chromatography and mass spectrometry has been developed and validated for the determination of broad polarity spectrum emerging pollutants, ethyl paraben, butyl paraben, diethyl phthalate, dibutyl phthalate, lidocaine, prilocaine, triclosan, and bisphenol A in various aqueous samples. Some important parameters of fabric phase sorptive extraction such as extraction time, matrix pH, stirring speed, type and volume of desorption solvent were investigated and optimized. Calibration curves were obtained in the concentration range 0.05–500 ng/mL. Under the optimum conditions, the limits of detection were in the range 0.009 –0.021 ng/mL. This method was validated by analyzing the compounds in spiked aqueous samples at different levels with recoveries of 93 to 99% and relative standard deviations of <6%. The developed method was applied for the determination of the emerging contaminants in tap water, municipal water, ground water, sewage water, and sludge water samples. The results demonstrate that fabric phase sorptive extraction has great potential in the preconcentration of trace analytes in complex matrix.