Rapid determination of corticosteroids in pharmaceuticals by flow injection analysis

The proposed method is based on the reduction of blue tetrazolium by the steroid in an alkaline medium to form a highly colored formazan. The effects of reagent concentration, temperature, flow rate, and manifold design on the reaction are discussed for a typical steroid, methylprednisolone acetate. Analytical readout is obtained within 30 s after sample introduction and up to 100 samples/h can be processed with baseline resolution between peaks. Typical relative standard deviations of 0.5% are obtained with 10-μ1 injection volumes. Results obtained by flow injection analysis are similar to those obtained with the AutoAnalyzer technique.     

The Dyeing of Nylon and Cotton Cloth with Azo Dyes: Kinetics and Mechanism

The mechanism of the dyeing of cotton and nylon cloth by the azo dyes Orange G and Sunset Yellow FCF was investigated using a channel flow cell. The variation in dyeing with flow rate was found to proceed via a mechanism in which the flux of dye entering the cloth relative to the flux of dye to the cloth surfacedecreasedwith increasing flow rate. A mechanism is deduced in which the dye passes from bulk solution, through a porous surface layer within the cloth, before passing into the bulk cloth. Adsorption onto surface sites in this porous layer blocks the passage of further dye into the cloth. Kinetic parameters for such a mechanism are given.     

A novel,stereoselective silyl-directed Stevens [1,2]-shift of ammonium ylides

[reaction: see text] The silyl group of 2-silylpyrrolidines such as 1 plays several critical roles: a stereochemical control element in a facially selective carbenoid addition to the ring nitrogen, a stereochemical "placeholder" during regioselective 1,2-migration with retention by the resulting spirocyclic ammonium ylide, and a hydroxyl surrogate for an eventual stereoselective Fleming-Tamao oxidation. This chemistry represents a novel use of the Stevens rearrangement and offers a short, enantioselective route to hydroxylated quinolizidines such as 3 from Boc-pyrrolidine.     

In situ soft X-ray studies of ethylene oxidation mechanisms and intermediates on the Pt(111) surface

In situ studies of ethylene oxidation on Pt(111) have been performed using a powerful combination of fluorescence yield soft X-ray methods for temperatures up to 600 K and oxygen pressures up to 0.01 Torr. Absolute carbon coverages have been determined both in steady-state and dynamic catalytic conditions on the Pt(111) surface. Fluorescence yield near-edge spectroscopy (FYNES) and temperature-programmed fluorescence yield near-edge spectroscopy (TP-FYNES) experiments above the carbon K edge were used to identify the structure and bonding of the dominant surface species during oxidation. TP-FYNES experiments of preadsorbed ethylene coverages in oxygen pressures up to 0.01 Torr indicate a stable intermediate is formed over the 215-300 K temperature range. By comparing the intensity of the C-H sigma resonance at the magic angle with the intensity in the carbon continuum, the stoichiometry of this intermediate has been determined explicitly. Based on calibration with known C-H stoichiometries, the intermediate has a C(2)H(3) stoichiometry for oxygen pressures up to 0.01 Torr, indicating oxydehydrogenation occurs before skeletal oxidation. FYNES spectra at normal and glancing incidences were performed to characterize the structure and bonding of this intermediate. Using FYNES spectra of ethylene, ethylidyne, and acetylene as reference standard, this procedure indicates the oxidation intermediate is tri-sigma vinyl. Thus, oxidation of ethylene proceeds through a vinyl intermediate, with oxydehydrogenation preceding skeletal oxidation.     

Analysis of anions in hydrofluoro ethers by ion chromatography

Hydrofluoro ethers (HFES) are considered to be an ideal cleaning solvent in applications like vapor degreasing and wet cleaning. It is also a good solvent replacement for CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons) and chlorinated solvents because they have a short atmospheric lifetime and low global warming potential. Based upon their properties, hydrofluoro ethers are ideally suited for the demands of the electronics industry. However, the electronics industry requires these solvents to have high purity, especially in the area of residual anions. This paper will present information on an extraction methodology for the transfer of anions from the hydrofluoro ether to water. Then, an analytical method utilizing ion chromatography that is capable of detection of 10 anions (fluoride, acetate, formate, chloride, nitrite, bromide, nitrate, sulfate, oxalate, and phosphate) in the part per billion level will be demonstrated.     

Synthesis and reactions of the transition metal substituted tin hydride HSn[Mo(CO)3C5H5]3

Reaction of HMo(CO)₃C₅H₅ and Sn(C₅H₅)₂ produces the tin hydride HSn[Mo(CO)₃C₅H₅]₃ (I). Reaction of I with CCl₄, CHCl₃, or CH₂Cl₂ gives ClSn[Mo(CO)₃C₅H₅]₃ (II). With hydrogen chloride the hydride I reacts to produce the dichloride Cl₂Sn[Mo(CO)₃C₅H₅]₂. The first step in this reaction is cleavage of the SnH bond to produce the chloride II. The hydride I reacts with acetic acid to produce the diacetate (CH₃COO)₂Sn[Mo(CO)₃C₅H₅]₂.     

The stannylation of carbonyl-stabilised phosphorus ylids,and tin-assisted elimination reactions

The interaction of organotin halides with lithium salts of mono-substituted phosphorus ylids and also with disubstituted ylids is described.     

Combinatorial invariants for nets of conics in $$\mathrm {PG}(2,q)$$ PG ( 2 , q )

Designs, Codes and Cryptography - The problem of classifying linear systems of conics in projective planes dates back at least to Jordan, who classified pencils (one-dimensional systems) of conics...     

Extremes of censored and uncensored lifetimes in survival data

Extremes - We consider a random censoring model for survival analysis, allowing the possibility that only a proportion of individuals in the population are susceptible to death or failure, and the...