A high performance liquid chromatographic post-column fluorescent ion pair extraction system: application to physostigmine and its metabolite eseroline in human serum

A high performance liquid chromatographic post-column fluorescent ion pair extraction system was developed for the analysis of quaternary ammonium and amine drugs in serum. A new fluorescent ion pair reagent, sodium alpha-(3,4-dimethoxyphenyl) cinnamonitrile-2'-sulfonate (DPS), was synthesized and characterized. The post-column extraction system consisted of a three-dimensional knitted teflon mixing coil and a membrane phase separator which was modified from an original literature design. Physostigmine and its metabolite eseroline were used as model cations. A solid phase extraction procedure using octadecylsilane columns was developed to extract the compounds and neostigmine bromide (internal standard) from human serum. The compounds were chromatographed on a diol column using a 80:20 aqueous phosphate buffer pH 4 absolute methanol mobile phase at a flow rate of 1 mL/min. Methylene chloride was used as the on-line extraction solvent for the DPS ion pairs formed. Fluorescence of the extracted ion pairs was measured using an excitation of 243 nm and an emission cut-off filter at 418 nm. Linearity was in the 2-100 ng/mL and 5-100 ng/mL ranges for physostigmine and eseroline, respectively. Detection limits based on a signal-to-noise ratio of 2, were 2 and 5 ng/mL, respectively. Precision of the method was found to be in the 1.5-3% range and percentage error in the 1.5-7% range for both compounds.     

Discovery of a superconducting A-15 phase in the V-Re system

A superconducting A-15 type phase of a very unusual stochiometry has been discovered in the vanadium-rhenium system. The phase is stable only above 1500°C and exists over a very limited homogeneity range near 29 atom percent vanadium. The lattice parameters range from 4.8774 to 4.8802 Å with the corresponding superconducting transition temperatures varying from 8.4 K to 7.6 K. X-ray diffraction shows that both Re and V atoms occupy the A-sites, only Re atoms are in the B-sites and there is no evidence of any superstructure. Specific heat measurements give values of γ = 4.03 mJ/g-atomK², β = 0.0285 mJ/g-atomK⁴ and θ_D = 409 K.     

The behavior of a multiplicity independent root-finding scheme in the presence of error

King and Kioustelidis independently proposed a derivative free scheme that permits root finding methods, such as the secant method to preserve high order convergence when the root in question is multiple. In this note it is shown that the scheme can fail to achieve the maximum accuracy that is attainable at a fixed precision of computation.This work was supported in part by the Office of Naval Research under contract No. N00014-76-C-0391.     

Fluorescence of dissociating fragments from supersonic jet-electron collisions

Supersonically cooled jets of nitrogen, methane, ethane, cyclopropane, and azomethane are crossed with collimated streams of electrons. The CH (B²Σ^? → X²Π) spectra resulting from the electron-induced dissociation of CH₄, C₂H₆, and CH₂)₃ can be fit with rotation temperatures between 4000 and 6000 K for an electron energy of 100 eV. Flourescence spectra of N₂⁺ (B²Σ_w⁺ → X²Π) from the dissociative ionization of azomethane yield a rotational temperature of =8×10³ K; from ionization of molecular nitrogen the rotational temperature of B²Σ_w⁺ N₂⁺ is 45 K. Mechanisms for these various processes are discussed.     

The band structures and magnetic properties of some transition-metal monophosphides I. Scandium phosphide

An improved method is described for the calculation of the band structures and density of states for three-dimensional solids. It is based on an LCAO-TB method. The method is applied to the scandium phosphide crystal. This material is calculated to be a semiconductor with a small band gap.