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Selected AbstractsElectrochemical Preparation of Poly(acriflavine) Film-Modified Electrode and Its Electrolcatalytic Properties Towards NADH, Nitrite and Sulfur OxoanionsELECTROANALYSIS, Issue 9 2007Shen-Ming Chen Abstract Electrochemical polymerization of acriflavine (AF) was carried out onto glassy carbon electrodes (GCE) from the aqueous buffer solution containing 1.5×10,3,M AF monomer (pH,3.5) which produced a thin electrochemically active film. This is noted as poly(AF) film modified electrodes (PAF/GCE). This modified electrode was shown a stable reversible redox couple centered at +0.22,V in pH,3.5 buffer solutions. PAF/GCE was found to be more stable in acidic solutions and its formal potential was found to be pH dependent with a slope close to ,60,mV/pH. The electrochemical deposition kinetics of poly(AF) onto gold coated quartz crystal was studied by using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). PAF/GCE was found be good mediator for electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) in pH,5 buffer solutions. The electrocatalytic oxidation of SO and electrocatalytic reduction of NO, SO and S2O were carried out at PAF/GCE electrode in acidic aqueous solutions. The electrocatalytic oxidation of NADH was also investigated by using amperometric method. [source] A novel method for deriving true density of pharmaceutical solids including hydrates and water-containing powdersJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2004Changquan (Calvin) Sun Abstract True density is commonly measured using helium pycnometry. However, most water-containing powders, for example, hydrates, amorphous drugs and excipients, and most tablet formulations, release water when exposed to a dry helium atmosphere. Because released water brings significant errors to the measured true density and drying alters the nature of water-containing solids, the helium pycnometry is not suitable for those substances. To overcome this problem, a novel method has been developed to accurately calculate powder true density from compaction data. No drying treatment of powder samples is required. Consequently, the true density thus obtained is relevant to tableting characterization studies because no alteration to the solid is induced by drying. This method involves nonlinear regression of compaction pressure-tablet density data based on a modified Heckel equation. When true density values of water-free powders derived by this novel method were plotted against values measured using pycnometry, a regression line with slope close to unity and intercept close to zero was obtained. Thus, the validity of this method was supported. Using this new method, it was further demonstrated that helium pycnometry always overestimates true densities of water containing powders, for example, hydrates, microcrystalline cellulose (MCC), and tablet formulations. The calculated true densities of powders were the same for different particle shapes and sizes of each material. This further suggests that true density values calculated using this novel method are characteristic of given materials and independent of particulate properties. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:646,653, 2004 [source] The poorly constrained cluster disruption time-scale in the Large Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Genevičve Parmentier ABSTRACT We use Monte Carlo simulations, combined with homogeneously determined age and mass distributions, based on multiwavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) star cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index ,=,2 assuming different cluster disruption time-scales. For each of these cluster disruption time-scales, we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a ,Poissonian',2 sense, model mass distributions and model two-dimensional distributions in log(mass) versus log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit (MlimV,,4.7 mag) above which the observed cluster sample is complete, one cannot constrain the characteristic cluster disruption time-scale for a 104 M, cluster, tdis4[where the disruption time-scale depends on cluster mass as tdis=tdis4(Mcl/104 M,),, with ,, 0.62], to better than a lower limit, tdis4, 1 Gyr. We conclude that the CFR has been increasing steadily from 0.3 clusters Myr,1 5 Gyr ago to a present rate of (20,30) clusters Myr,1 for clusters spanning a mass range of ,100,107 M,. For older ages, the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from ,1 cluster Gyr,1 15 Gyr ago to its present value. On the other hand, if the ICMF has always been a power law with a slope close to ,=,2, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution. [source] Direct quantification of 11-nor-,9 -tetrahydrocannabinol-9-carboxylic acid in urine by liquid chromatography/tandem mass spectrometry in relation to doping control analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2010C. Chebbah An accurate and precise method for the quantification of 11-nor-,9 -tetrahydrocannabinol-9-carboxylic acid (THCA) in urine by liquid chromatography/tandem mass spectrometry (LC/MS/MS) for doping analysis purposes has been developed. The method involves the use of only 200,µL of urine and the use of D9 -THCA as internal standard. No extraction procedure is used. The urine samples are hydrolysed using sodium hydroxide and diluted with a mixture of methanol/glacial acetic acid (1:1). Chromatographic separation is achieved using a C8 column with gradient elution. All MS and MS/MS parameters were optimised in both positive and negative electrospray ionisation modes. For the identification and the quantification of THCA three product ions are monitored in both ionisation modes. The method is linear over the studied range (5,40,ng/mL), with satisfactory intra-and inter-assay precision, and the relative standard deviations (RSDs) are lower than 15%. Good accuracy is achieved with bias less than 10% at all levels tested. No significant matrix effects are observed. The selectivity and specificity are satisfactory, and no interferences are detected. The LC/MS/MS method was applied for the analysis of 48 real urine samples previously analysed with a routine gas chromatography/mass spectrometry (GC/MS) method. A good correlation between the two methods was obtained (r2,>,0.98) with a slope close to 1. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||