PRESENTATIONS: FROM KAC-MOODY GROUPS TO PROFINITE AND BACK

We go back and forth between, on the one hand, presentations of arithmetic and Kac-Moody groups and, on the other hand, presentations of profinite groups, deducing along the way new results on both.     

Spectrophotometric determination of flucloxacillin in pharmaceutical preparations using some nitrophenols as a complexing agent

Some nitrophenols are proposed as chromogenic reagents for the spectrophotometric determination of flucloxacillin. The reagent forms a greenish yellow 1:1 complex with flucloxacillin at pH 9.0. This complex is stable for at least 3.0 h after its formation. The greenish yellow charge transfer complex species has an absorption maximum at 446, 435, 442, 473 and 439 nm for p-nitrophenol (I), 2,4-dinitrophenol (II), 3,5-dinitrosalycilic acid (III), picramic acid (IV) and picric acid (V), respectively, with a molar absorptivity between 1.43 x 10(4) and 2.59 x 10(4) l mol(-1) cm(-1). Beer's low is valid over the concentration range 2.0-40 microg ml(-1) of flucloxacillin. The detection and quantitation limits as well as relative standard deviation were also calculated. The reagents have been successfully used for the spectrophotometric determination of flucloxacillin in pure form and in pharmaceutical preparations.     

Embeddings of SL(2; ?) into the cremona group

Geometric and dynamic properties of embeddings of SL(2; ℤ) into the Cremona group are studied. Infinitely many nonconjugate embeddings that preserve the type (i.e., that send elliptic, parabolic and hyperbolic elements onto elements of the same type) are provided. The existence of infinitely many nonconjugate elliptic, parabolic and hyperbolic embeddings is also shown. In particular, a group G of automorphisms of a smooth surface S obtained by blowing up 10 points of the complex projective plane is given. The group G is isomorphic to SL(2; ℤ), preserves an elliptic curve and all its elements of infinite order are hyperbolic.     

Assessment of matrix effects and determination of niacin in human plasma using liquid-liquid extraction and liquid chromatography-tandem mass spectrometry

A simple, sensitive and rapid liquid-liquid extraction method for the analysis of nicotinic acid (niacin) and its labeled internal standard nicotinic acid-d4 (niacin-d4) in human plasma was developed and validated. The analyte and its internal standard were isolated from acidified plasma using a single liquid-liquid extraction procedure with methyl-t-butyl ether. The extracted samples were analyzed by liquid chromatography-tandem mass spectrometry in positive electrospray ionization mode with multiple reaction monitoring. The calibration curves were linear in the measured range between 5 and 1000 ng/mL and the limit of detection was calculated as 122 pg/mL. The method required 250 microL of human plasma and the total run time between injections was 3.5 min. Matrix effects were assessed by post-column infusion experiments, phospholipids monitoring and post-extraction addition experiments. The extraction of phospholipids and niacin from plasma was studied under acidic, neutral and basic conditions. Acidic conditions were optimal for both the recovery of niacin and the removal of phospholipids; the degree of matrix effects for niacin was determined to be 2.5%. It was concluded that effective removal of matrix components can overcome low recovery issues associated with liquid-liquid extractions of polar analytes.     

New Colorimetric Methods for the Determination of Indapamide and its Formulations

 Two simple and sensitive methods for the determination of indapamide in pure and in dosage forms are developed. These methods are based on the oxidation of indapamide with iron(III) in acidic medium. The liberated iron(II) reacts with 1,10-phenanthroline (Method A) and the ferroin complex is colorimetrically measured at λ_max 509 nm against reagent blank. Method B is based on the reduction of Fe(III) by the drug. Iron(II) forms a colored complex (λ_max 522 nm) with 2,2′-bipyridyl. Optimization of the experimental conditions is described. Beer’s law is obeyed in the concentration range 1.0–12 μg ml⁻¹ and 4.0–18 μ g ml⁻¹ for A and B, respectively. The apparent molar absorptivity and Sandell sensitivity for method A is 3 × 10⁴ L mol⁻¹ cm⁻¹ and 0.0188 μ g cm⁻², while for method B is 2.3 × 10⁴ L mol⁻¹ cm⁻¹ and 0.0159 μg cm⁻². The detection and quantification limits are calculated. The developed methods are applied successfully for the determination of indapamide in pure and in tablet form without interference from common excepients. Received November 10, 2000. Revision April 6, 2001.