Perfluorinated acids as ion-pairing agents in the determination of monoamine transmitters and some prominent metabolites in rat brain by high-performance liquid chromatography with amperometric detection

The behaviour of trifluoroacetate and heptafluorobutyrate as pairing ions for the reversed-phase ion-pair separation of monoamine transmitters and related metabolites was studied. The performance of systems with the perfluorinated acids was compared with that of systems containing sodium octyl sulphonate and was found to be better in terms of peak resolution combined with total analysis time, day-to-day reproducibility and the time required for attaining initial chromatographic equilibrium. Rat brain samples were deproteinized in the acidified mobile phase, injected directly on to a high-performance liquid chromatographic column and quantitated using an amperometric detector. Sample run times were 6-8 min, at a relatively low flow-rate. The detection limits achieved are fairly uncommon with conventional bore columns. The two perfluorinated acids studied differ in the dominant mechanisms of ion-pair formation and show selectivity differences as a result.     

A theoretical study of the structure and stability of borohydride on 3d transition metals

The adsorption of borohydride on 3d transition metals (Cr, Mn, Fe, Co, Ni and Cu) was studied using first principles calculations within spin-polarized density functional theory. Magnetic effect on the stability of borohydride is noted. Molecular adsorption is favorable on Co, Ni and Cu, which is characterized by the strong s–d_zz hybridization of the adsorbate-substrate states. Dissociated adsorption structure yielding one or two H adatom fragments on the surface is observed for Cr, Mn and Fe.     

Electrochemical formation of a Pt/Zn alloy and its use as a catalyst for oxygen reduction reaction in fuel cells

The characterization of an electrochemically created Pt/Zn alloy by Auger electron spectroscopy is presented indicating the formation of the alloy, the oxidation of the alloy, and the room temperature diffusion of the Zn into the Pt regions. The Pt/Zn alloy is stable up to 1.2 V/RHE and can only be removed with the oxidation of the base Pt metal either electrochemically or in aqua regia. The Pt/Zn alloy was tested for its effectiveness toward oxygen reduction. Kinetics of the oxygen reduction reaction (ORR) were measured using a rotating disk electrode (RDE), and a 30 mV anodic shift in the potential of ORR was found when comparing the Pt/Zn alloy to Pt. The Tafel slope was slightly smaller than that measured for the pure Pt electrode. A simple procedure for electrochemically modifying a Pt-containing gas diffusion electrode (GDE) with Zn was developed. The Zn-treated GDE was pressed with an untreated GDE anode, and the created membrane electrode assembly was tested. Fuel cell testing under two operating conditions (similar anode and cathode inlet pressures, and a larger cathode inlet pressure) indicated that the 30 mV shift observed on the RDE was also evident in the fuel cell tests. The high stability of the Pt/Zn alloy in acidic environments has a potential benefit for fuel cell applications.     

Cultivating conditions optimization of the anaerobic digestion of corn ethanol distillery residuals using response surface methodology

This study investigated the individual and interactive effects of three factors — temperature, inoculum/substrate ratio (ISR) and inoculum typology — on the anaerobic digestion of corn ethanol distillery wastewater. Biochemical methane potential assays planned with factorial design with two independent quantitative variables on three levels (ISR: 1:1, 2:1 and 3:1; temperature: 30°C, 33.5°C, 37°C) and one independent qualitative variable (inoculum type: suspended, granular, mixed) have been performed. Response Surface Methodology has been used to study the effect of the factors with the aim of maximizing the specific methane yields (Y_CH4) obtainable with this substrate. The results show that all three investigated factors influence in a significant matter the Y_CH4, the ISR having the strongest effect on it. The temperature has significant influence on the Y_CH4 only in combination with high ISR values. The optimal conditions for the maximum Y_CH4 (551 mL CH₄ g^?1 VS_added) have been found at 37°C operating temperature, ISR=3:1 and using granular inoculum. These conditions gave rise to a 4-fold increase of Y_CH4 with respect to the worst combination of factors (Y_CH4=129 mL g^?1 VS_added for the suspended inoculum type, at 30°C and ISR=1:1). The results improve the knowledge on the digestion of this substrate, providing information for successful process up-scaling.

Open image in new window

     

The critical bromide concentration in an oscillating chemical system

A new method for the determination of aluminium in biological fluids by flameless atomic absorption spectrometry is described. A wetting agent (Teepol) is added to shorten the time of drying and ashing steps and to improve reproducibility. Aluminium is converted to aluminate with ammonia liquor to prevent volatile chloride formation. Application of the method to a serum gave results with a relative standard deviation of 2.5%. This method was also applied to the determination of aluminium in serum and cerebrospinal fluid of 20 normal persons: the mean value for the sera was 34.1 μg 1^-1 and the mean value for the CSF was 19.8 μg 1^-1 with relative standard deviations of 3.5% and 2.5%, respectively.     

Measurement of K-27, an oxime-type cholinesterase reactivator by high-performance liquid chromatography with electrochemical detection from different biological samples

K-27 is a bisquaternary asymmetric pyridinium aldoxime-type cholinesterase reactivator of use in the treatment of poisoning with organophosphorous esterase inhibitors. A sensitive, simple and reliable reverse-phase high-performance liquid chromatographic method with electrochemical detection was developed for the measurement of K-27 concentrations in rat brain, cerebrospinal fluid, serum and urine samples. Male Wistar rats were treated intramuscularly with K-27 and the samples were collected 60 min later. Separation was carried out on an octadecyl silica stationary phase and a disodium phosphate solution (pH 3.7) containing citric acid, octane sulphonic acid and acetonitrile served as mobile phase. Measurements were carried out at 30 degrees C at E(ox) 0.65 V. The calibration curve was linear through the range of 10-250 ng/mL. Accuracy, precision and the limit of detection calculated were satisfactory according to internationally accepted criteria. Limit of quantitation was 10 ng/mL. The method developed is reliable and sensitive enough for monitoring K-27 levels from different biological samples including as little as 10 microL of cerebrospinal fluid. The method--with slight modification in the composition of the mobile phase--can be used to measure a wide range of other related pyridinium aldoxime-type cholinesterase reactivators.     

Hilbert scheme of points on cyclic quotient singularities of type (<Emphasis Type="Italic">p</Emphasis>, 1)

In this note we investigate the generating series of the Euler characteristics of the Hilbert scheme of points on cyclic quotient singularities of type (p, 1). We link the appearing combinatorics to p-fountains, a generalization of the notion of fountain of coins. We obtain a representation of the generating series as a coefficient of a two variable generating series.