Adsorptive stripping voltammetry of bovine serum albumin

The behaviour of bovine serum albumin in cyclic voltammetry and differential-pulse adsorptive stripping voltammetry is described. Under the optimized conditions, with an accumulation potential of +0.15 V (vs. Ag/AgCl) and accumulation times of 50 s or 120 s, linear calibration graphs were obtained for 1.0–4.0×10^?8 M BSA and 0.2–1.5×10^?8 M BSA, respectively.     

Characterisation of nicotine and related compounds using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their detection by liquid chromatography/electrospray ionisation mass spectrometry

Electrospray ionisation ion trap mass spectrometry (ESI-MS(n)) has been used to study the fragmentation patterns of nicotine and nine of its related compounds. From this study certain characteristic fragmentations are apparent with generally the pyrrolidine or piperidine ring being subject to chemical modifications. The structures of the product ions proposed for the ESI-MS(n) study have been supported by results from electrospray ionisation quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). Compounds with pyrrolidine and piperidine rings that possess an unsubstituted N atom have been shown to lose NH(3) at the MS(2) stage. Those compounds with N-methyl groups lose CH(3)NH(2) at the MS(2) stage. The loss of NH(3) or CH(3)NH(2) leaves the corresponding rings opened and this is followed by ring closure at the pyridine-2 carbon atom. Mono-N-oxides fragment in a similar way but the di-N-oxide can also fragment by cleavage of the bond between the pyridine and pyrrolidine rings. Cotinine also can undergo cleavage of this bond between the rings.This data therefore provides useful information on how substituents and the nature of the non-pyridine ring can affect the fragmentation patterns of nicotine and its related compounds. This information can be used in the characterisation of these compounds by liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) which results in the separation of nicotine and its related compounds with limits of detection (LODs) ranging from 15 to 105 ng/mL. The use of LC/ESI-MS to study nicotine-containing samples resulted in the simultaneous and unambiguous identification of seven of the compounds discussed in this paper: cotinine identified at retention time 12.5 min (with its [M+H](+) ion at m/z 177), nornicotine 16.0 min (m/z 149), anatabine 18.0 min (m/z 161), myosmine 18.5 min (m/z 147), anabasine 20.4 min (m/z 163), nicotine 22.2 min (m/z 163), and nicotyrine 31.4 min (m/z 159). For quality control of nicotine replacement therapy products, these nicotine impurities can be readily identified and determined at levels up to 0.3% for single impurities and up to 1.0% for total impurities.     

Analytical Chemistry for the life sciences

Summary A course on Analytical Chemistry for the life sciences currently conducted at the Chemistry Department of Chelsea College, London, is described. This course has three main components: Lectures on the analysis of materials of biological importance, practical experiments using both chemical and instrumental methods, and lectures from experts of other departments on specialized fields of application.

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Analytische Chemie für die Biowissenschaften

Zusammenfassung Ein Ausbildungsplan für Analytische Chemie wird beschrieben wie er gegenwärtig in der chemischen Abteilung des Chelsea College, London, für Biowissenschaftler in Anwendung ist. Die Ausbildung umfaßt folgende drei Teile: Vorlesungen über die Analyse von biologisch relevanten Materialien, Praktika in chemischen und instrumentellen Analysenmethoden und Vorlesungen von einschlägigen Experten über spezielle Anwendungsgebiete.

     

AFPP vs FPP

The main theme of this paper is that almost fixed point properties of discrete structures and fixed point properties of (topological) spaces are interdeducible via a suitable category which contains both graphs and spaces as objects. To carry out the program, we have to consider (almost) fixed points of multifunctions, and for this we need a preliminary discussion of power structures for graphs and simplicial complexes. Specific applications developed are: a digital convexity (discrete) version of Kakutani's fixed point theorem for convex-valued multifunctions; and fixed point properties of dendrites in terms of those of finite discrete trees.     

Zero-Mean Cosine Polynomials which are Non-Negative for as Long as Possible

For a given integer n, all zero-mean cosine polynomials of orderat most n which are non-negative on [0,(n/(n+1))] are found,and it is shown that this is the longest interval [0,] on whichsuch cosine polynomials exist. Also, the longest interval [0,]on which there is a non-negative zero-mean cosine polynomialwith non-negative coefficients is found. As an immediate consequence of these results, the correspondingproblems of the longest intervals [,] on which there are non-positivecosine polynomials of degree n are solved. For both of these problems, all extremal polynomials are found.Applications of these polynomials to Diophantine approximationare suggested.     

Bioavailability studies of oral dosage forms containing levodopa and carbidopa using column-switching chromatography followed by electrochemical detection

A reliable multi-dimensional column chromatographic method employing amperometric detection using a carbon fibre microelectrode procedure was used for monitoring the plasma profiles and to evaluate the pharmacokinetics and bioavailability of levodopa (L-dopa) and carbidopa (C-dopa), after ingestion of oral formulations containing these drugs. The peak currents obtained for the different analytes were directly proportional to the analyte over the concentration range 0.02-4 micrograms ml-1. Using this method, the minimum detectable concentration was estimated to be 5 and 8 ng ml-1 for L-dopa and C-dopa, respectively. Recovery studies ranged from 93.83 to 89.76%, with a relative standard deviation of less than 7%. The study was carried out in two separate weeks on five healthy non-patient fasted male/female volunteers in the age range 20-37 years and weighing between 60 kg and 78 kg. The pharmacokinetic profile of two controlled-release products containing both L-dopa and C-dopa (Sinemet CR3 and CR4) was compared on the one hand and Sinemet conventional tablets on the other. The pharmacokinetic parameters, peak concentration (Cmax), the time taken to obtain this level (Tmax), elimination half-time T1/2, elimination rate constant (Kel), plasma level ratio, fluctuation index (FI) and the area under the time-concentration curve (AUC0-8), were investigated for each individual formulation. A comparison of the uptake of L-dopa from the conventional formulation showed that L-dopa entered the plasma and achieved peak levels higher than that of the controlled release formulations. However, it showed a much higher fluctuation index and the plasma concentrations were more stable with the controlled release formulations. The data also indicated a very low accumulation of both levodopa and carbidopa following repeated administration of the drugs, which was consistent with their relatively short half-lives (less than 2 h). In contrast, the half-life for the metabolite 3-orthomethyl dopa (3-OMD) is in the order of 13 h. As a result, there was an extensive accumulation of 3-OMD and its levels were significantly higher than those of levodopa or carbidopa upon repeated administration. Urine recoveries of the three analytes over one 8 h dosing interval showed that the majority of the excreted levodopa and carbidopa was recovered during the first 4 h, and there is proportionally greater excretion of the carbidopa dose than the levodopa dose.     

Asymptotic description of solitary wave trains in fully nonlinear shallow-water theory

We derive an asymptotic formula for the amplitude distribution in a fully nonlinear shallow-water solitary wave train which is formed as the long-time outcome of the initial-value problem for the Su–Gardner (or one-dimensional Green–Naghdi) system. Our analysis is based on the properties of the characteristics of the associated Whitham modulation system which describes an intermediate “undular bore” stage of the evolution. The resulting formula represents a “non-integrable” analogue of the well-known semi-classical distribution for the Korteweg–de Vries equation, which is usually obtained through the inverse scattering transform. Our analytical results are shown to agree with the results of direct numerical simulations of the Su–Gardner system. Our analysis can be generalised to other weakly dispersive, fully nonlinear systems which are not necessarily completely integrable.     

Application of electrospray mass spectrometry in the detection and determination of Remazol textile dyes.

The electrospray (ES) behaviour of selected Remazol textile dyes, their hydrolysis products and the latters' reaction, following elution from a strong anion-exchange cartridge, with 30% concentrated HCl in MeOH, is studied and applied to the direct analysis of dye containing effluent. For unambiguous identification and determination of these textile dyes in effluents, it is necessary to resort to ES utilising MS-MS and MS3. Further, a tabular review of recent applications of HPLC-ES-MS and, to a lesser extent, CE-ES-MS with reference to drug and pesticide analysis is presented.