Pharmaceutical applications of isoelectric focusing on microchip with imaged UV detection

For the first time, the application of a commercial Shimadzu microchip electrophoresis system MCE-2010 equipped with an imaging UV detector for isoelectric focusing (IEF) of therapeutic proteins is reported. By proper adjustment of the pH gradient, samples with pI values ranging from 2.85 to 10.3 can be focused to the imaged part of the separation channel. Three therapeutic proteins (hirudin, erythropoietin, and bevacizumab) have been successfully focused on the microchip, and the results have been compared to conventional capillary IEF in terms of peak profile, pI values, and reproducibility.     

Preparative free‐flow electrophoretic offline ESI‐Fourier transform ion cyclotron resonance/MS analysis of Suwannee River fulvic acid

Free‐flow electrophoresis (FFE), a preparative free zone electrophoretic method, was used offline in conjunction with ultrahigh‐resolution FT/ion cyclotron resonance ‐MS to resolve the complexity of Suwannee River fulvic acid (SRFA). Before MS, the FFE separation conditions and the compatibility with ESI were optimized. The constituents in SRFA were effectively separated based on their charge states and sizes. The obtained mass spectra were compared by means of van Krevelen diagrams and the calculated aromaticity indices of the individual constituents were used to describe the distribution of aromatic/unsaturated structures across the FFE‐fractionated samples. The consolidated number of ions observed within the individual SRFA fractions were much higher than those of the bulk samples alone, demonstrating extensive ion suppression effects in bulk SRFA likely also operating in the analysis of complex biogeochemical mixtures in flow injection mode. The FFE approach allows for producing sizable amounts of sample from dilute solutions, which can be easily fractionated into dozens of individual samples with the possibility of further in‐depth characterization.     

On-line photo-oxidation for the determination of organoarsenic compounds by atomic-absorption spectrometry with continuous arsine generation

A method has been developed for on-line conversion of organoarsenicals into arsenate, which is readily detected by atomic-absorption spectrometry with continuous arsine generation. The photoreactor consists of a mercury lamp wrapped with 5 m of PTFE tubing (0.5 mm i.d.). The photo-oxidation conditions were optimized, with a flow-injection analysis procedure, for arsenobetaine, monomethylarsonic acid, dimethylarsinic acid, o-arsanilic acid, and phenylarsonic acid, all organoarsenicals of biological and environmental importance. Solutions were continuously pumped at a flow-rate of 2.0 ml/min and combined with a stream of potassium persulfate (flow-rate 0.6 ml/min) before entering the photo-reactor. With reactor dwell times of 36 sec, conversion efficiencies for these compounds were above 95% under these conditions. Interfacing of this flow-through conversion and detection system with a chromatographic inlet permits real-time analysis of mixtures of these organoarsenic compounds, in a manner suitable for environmental or biomedical samples.     

Determination of vitamin B5 in a range of fortified food products by reversed-phase liquid chromatography-mass spectrometry with electrospray ionisation

Methods for Vitamin B5 determination in food products remain limited by their low sensitivity and poor selectivity. Here, we have developed a liquid chromatography-mass spectrometry (LC-MS) method for Vitamin B5 determination in wide range of fortified food products. Vitamin B5 was extracted from food samples by heat treatment and analysed by LC-MS in the positive mode using electrospray ionisation (ESI). Vitamin B5 was quantified using hopantenic acid (HOPA) as internal standard after their separation on a C18 narrow-bore column with a gradient of mobile phase made of water/acetonitrile and trifluoroacetic acid (TFA) 0.025%. MS with single ion monitoring mode at mass m/z 220 was used for Vitamin B5 quantification. Calibration curve between 0.5 and 10 microg/ml of Vitamin B5 was linear (r2=0.9993) and the detection limit was determined to be 800 pg. The overall quantitative efficiency of the method was evaluated using Nestle reference sample (infant formula). The intra-assay RSD was 4.8% (n=8), the inter-assay RSD 6.4% (n=4) and the recoveries of the spiked samples were above 95%. Application of the LC-MS method to Vitamin B5 determination in wide range of fortified food products including three US National Institute of Standards and Technology (NIST) reference samples (RM 8435, RM 8415 and SRM 1546) shows consistent results with those obtained by microbiology and recoveries of Vitamin B5 between 93 and 104% for the spiked samples.     

Forced nonlinear oscillations of elastic membranes

An initial-boundary-value problem is considered for the spatially two-dimensional damped Boussinesq equation with a forcing term. The problem in question is argued to serve as a model for describing small nonlinear oscillations of a circular membrane under the influence of acoustic pressure. Eigenfunction expansion method is used for constructing the global-in-time solution of the problem in question. Existence and uniqueness follow from the construction. Long-time asymptotics is computed on the basis of the obtained series representation. Numerical simulations are conducted. The algorithm shows excellent convergence properties.     

Combined utilization of ion mobility and ultra‐high‐resolution mass spectrometry to identify multiply charged constituents in natural organic matter

Natural organic matter as complex biogeochemical non‐repetitive material was investigated with ion mobility mass spectrometry (IMS) and ultra‐high‐resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS) approaches in order to unravel the existence of multiply charged state constituents. Hereby we describe and assign the potential molecular formulae of these doubly charged species, derived from FTICR‐MS, and the existence of these species was confirmed via IMS. The parallel application of these powerful techniques enabled the boundaries of the understanding of natural organic matter to be pushed further. Copyright © 2009 John Wiley & Sons, Ltd.