Chromatography

Photoactivation by visible light of CdTe quantum dots for inline generation of reactive oxygen species in an automated multipumping flow system

ScienceDirect Publication: Analytica Chimica Acta — Sun, 27 May 2012 08:44:37 +0000

Publication year: 2012
Source:Analytica Chimica Acta

David S.M. Ribeiro, Christian Frigerio, João L.M. Santos, João A.V. Prior

Quantum dots (QD) are semiconductor nanocrystals able to generate free radical species upon exposure to an electromagnetic radiation, usually in the ultraviolet wavelength range. In this work, CdTe QD were used as highly reactive oxygen species (ROS) generators for the control of pharmaceutical formulations containing epinephrine. The developed approach was based on the chemiluminometric monitoring of the quenching effect of epinephrine on the oxidation of luminol by the produced ROS. Due to the relatively low energy band-gap of this chalcogenide a high power visible light emitting diode (LED) lamp was used as photoirradiation element and assembled in a laboratory-made photocatalytic unit. Owing to the very short lifetime of ROS and to ensure both reproducible generation and time-controlled reaction implementation and development, all reactional processes were implemented inline by using an automated multipumping micro-flow system. A linear working range for epinephrine concentration of up to 2.28×10⁻⁶ molL⁻¹ (r=0.9953; n=5) was verified. The determination rate was about 79 determinations per hour and the detection limit was about 8.69×10⁻⁸ molL⁻¹. The results obtained in the analysis of epinephrine pharmaceutical formulations by using the proposed methodology were in good agreement with those furnished by the reference procedure, with relative deviations lower than 4.80%.

Graphical abstract

Graphical abstract Highlights

► CdTe quantum dots generate free radical species upon exposure to visible radiation. ► A high power visible LED lamp was used as photoirradiation element. ► The laboratory-made LED photocatalytic unit was implemented inline in a MPFS. ► Free radical species oxidize luminol producing a strong chemiluminescence emission. ► Epinephrine scavenges free radical species quenching chemiluminescence emission.

Determination of organphosphorus pesticides in ecological textiles by solid-phase microextraction with a siloxane-modified polyurethane acrylic resin fiber

ScienceDirect Publication: Analytica Chimica Acta — Sun, 27 May 2012 08:44:37 +0000

Publication year: 2012
Source:Analytica Chimica Acta

Xianlei Hu, Mingqiu Zhang, Wenhong Ruan, Fang Zhu, Gangfeng Ouyang

A novel solid-phase microextraction (SPME) fiber coating was prepared with siloxane-modified polyurethane acrylic resin by photo-cured technology. The ratio of two monomers was investigated to obtain good microphase separation structure and better extraction performance. The self-made fiber was then applied to organophosphorus pesticides (OPPs) analysis and several factors, such as extraction/desorption time, extraction temperature, salinity and pH, were studied. The optimized conditions were: 15min extraction at 25°C, 5% Na2SO4 content, pH 7.0 and 4min desorption in GC inlet. The self-made fiber coating exhibited better extraction efficiency for OPPs, compared with three commercial fiber coatings. Under the optimized conditions, the detection limits of 11 OPPs were from 0.03μgL⁻¹ to 0.5μgL⁻¹. Good recoveries and repeatabilities were obtained when the method was used to determine OPPs in ecological textile.

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Graphical abstract Highlights

► A PUSA/PETA SPME fiber coating was prepared by photo-cured technology ► The ratio of two monomers was optimized for better extraction performance ► The fiber showed very good performance for OPPs analysis in textiles.

The surface-plasmon-resonance effect of nanogold/silver and its analytical applications

ScienceDirect Publication: TrAC Trends in Analytical Chemistry — Sat, 26 May 2012 21:37:00 +0000

Publication year: 2012
Source:TrAC Trends in Analytical Chemistry

Aihui Liang, Qingye Liu, Guiqing Wen, Zhiliang Jiang

Gold and silver nanoparticles (Au/AgNPs) are widely used in analytical chemistry, and their intense colors have inspired artists and fascinated scientists.

This review describes the absorption and Rayleigh-scattering effects of the surface-plasmon resonance (SPR) of Au/AgNPs. Specifically, the color associated with Au/AgNPs is utilized for immunoassay and aptamer assays. SPR-Rayleigh scattering is used for nanoanalysis, when combined with immune, aptamer and nanocatalysis reactions.

Highlights

► We review gold/silver-SPR absorption and SPR-Rayleigh-scattering effects. ► SPR absorption has been utilized for immunoassay and aptamer assay. ► SPR-Rayleigh scattering has been used for immune, aptamer and nanocatalytic analysis.

Active Cellular Sensing with Quantum Dots: Transitioning from Research Tool to Reality

ScienceDirect Publication: Analytica Chimica Acta — Sat, 26 May 2012 21:36:54 +0000

Publication year: 2012
Source:Analytica Chimica Acta

James B. Delehanty, Kimihiro Susumu, Rachel L. Manthe, W. Russ Algar, Igor L. Medintz

The application of luminescent semiconductor quantum dots (QDs) within a wide range of biological imaging and sensing formats is now approaching its fifteenth year. The unique photophysical properties of these nanomaterials have long been envisioned as having the potential to revolutionize biosensing within cellular studies that rely on fluorescence. However, it is only now that these materials are making the transition towards accomplishing this goal. With the idea of understanding how to actively incorporate QDs into different types of cellular biosensing, we review the progress in many of the areas relevant to achieving this goal. This includes the synthesis of the QDs themselves, with an emphasis on minimizing potential toxicity, along with the general methods for making these nanocrystalline structures stable in aqueous media. We next survey some methods for conjugating QDs to biomolecules to allow them to participate in active biosensing. Lastly, we extensively review many of the applications where QDs have been demonstrated in an active role in cellular biosensing. These formats cover a wide range of possibilities including where the QDs have contributed to: monitoring the cell's interaction with its extracellular environment; elucidating the complex molecular interplay that characterizes the plasma membrane; understanding how cells continuously endocytose and exocytose materials across the cellular membrane; visualizing organelle trafficking; and, perhaps most importantly, monitoring the intracellular presence of target molecules such as nucleic acids, nutrients, cofactors, and ions or, alternatively, intracellular responses to external changes in the environment. We illustrate these processes with examples from the recent literature and focus on what QDs can uniquely contribute along with discussing the benefits and liabilities of each sensing strategy. A perspective on where this field is expected to develop in both the near and long-term is also provided.

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Graphical abstract Highlights

► Quantum dots (QDs) have evolved beyond mere cellular labeling reagents ► Significant advances made in QD materials, surface coatings and bioconjugation ► Cellular targeting/delivery been achieved using polymers, peptides, proteins ► Numerous QD-based sensing applications: extracellular, membrane, intracellular.

Foreword for Analytica Chimica Acta Volume 750

ScienceDirect Publication: Analytica Chimica Acta — Sat, 26 May 2012 21:36:54 +0000

Publication year: 2012Source:Analytica Chimica ActaPaul Worsfold, Ulli Krull, Alan Townshend

Simultaneous determination of asymmetric and symmetric dimethylarginine, L–monomethylarginine, L-arginine, and L-homoarginine in biological samples using stable isotope dilution liquid chromatography tandem mass spectrometry

ScienceDirect Publication: Journal of Chromatography B — Sat, 26 May 2012 18:59:26 +0000

Publication year: 2012
Source:Journal of Chromatography B

Mariska Davids, Eliane Swieringa, Fredrik Palm, Desirée E.C. Smith, Yvo M. Smulders, Peter G. Scheffer, Henk J. Blom, Tom Teerlink

Production of the endogenous vasodilator nitric oxide (NO) from L-arginine by NO synthase is modulated by L-homoarginine, L-monomethylargine (MMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). Here we report on a stable isotope dilution liquid chromatography tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of these metabolites in plasma, cells and tissues. After addition of the internal standards (D7-ADMA, D4-L-homoarginine and ¹³C6-L-arginine), analytes were extracted from the samples using Waters Oasis MCX solid phase extraction cartridges. Butylated analytes were separated isocratically on a Waters XTerra MS C18 column (3.5μm, 3.9×100mm) using 600mg/L ammonium formate in water - acetonitrile (95.5:4.5, v/v) containing 0.1 vol% formic acid, and subsequently measured on an AB Sciex API 3000 triple quadrupole mass spectrometer. Multiple reaction monitoring in positive mode was used for analyte quantification. Validation was performed in plasma. Calibration lines were linear (r² ≥ 0.9979) and lower limits of quantification in plasma were 0.4nM for ADMA and SDMA and 0.8nM for the other analytes. Accuracy (% bias) was<3% except for MMA (< 7%), intra–assay precision (expressed as CV) was<3.5%, inter-assay precision<9.6%, and recovery 92.9 - 103.2% for all analytes. The method showed good correlation (r² ≥ 0.9125) with our previously validated HPLC-fluorescence method for measurement in plasma, and was implemented with good performance for measurement of tissue samples. Application of the method revealed the remarkably fast (i.e. within 60min) appearance in plasma of stable isotope-labeled ADMA, SDMA, and MMA during infusion of D3-methyl-1-¹³C-methionine in healthy volunteers.

Highlights

► The endogenous vasodilator nitric oxide (NO) is produced from arginine by NO synthase ► Homoarginine and the methylated arginines MMA, ADMA, and SDMA modulate NO production ► An LC-MS/MS method for the simultaneous measurement of these compounds was developed ► Stable isotope labeled arginine, homoarginine and ADMA served as internal standards ► The method was validated for plasma and is also suitable for analysis of tissue samples.

Production, recovery and purification of a recombinant β-galactosidase by expanded bed anion exchange adsorption

ScienceDirect Publication: Journal of Chromatography B — Sat, 26 May 2012 18:59:26 +0000

Publication year: 2012
Source:Journal of Chromatography B

Valeria Boeris, Izabella Balce, Rami Reddy Vennapusa, Miguel Arévalo Rodríguez, Guillermo Picó, Marcelo Fernández Lahore

β-galactosidase is a hydrolase enzyme that catalyzes the hydrolysis of β-galactosides into monosaccharides; its major application in the food industry is to reduce the content of lactose in lactic products. The aim of this work is to recover this enzyme from a cell lysate by adsorption onto Streamline-DEAE in an expanded bed, avoiding, as much as possible, biomass deposition onto the adsorbent matrix. So as to achieve less cell debris - matrix interaction, the adsorbent surface was covered with polyvinyl pyrrolidone. The enzyme showed to bind in the same extent to naked and covered Streamline-DEAE (65mg β-gal/g matrix) in batch mode in the absence of any biomass. The kinetics of the adsorption process was studied and no effect of the polyvinyl pyrrolidone covering was found. The optimal conditions for the recovery were achieved by using a lysate made of 40% wet weight of cells, a polyvinyl pyrrolidone-covered matrix/lysate ratio of 10% and carrying out the adsorption process in expanded bed with recirculation over 2hours in 20mM phosphate buffer pH 7.4. The fraction recovered after the elution contained 65% of the initial amount of enzyme with a 12.6 fold increased specific activity with respect to the lysate. The polyvinyl pyrrolidone content in the eluate was determined and found negligible. The remarkable point of this work is that it was possible to partially purify the enzyme using a feedstock containing an unusually high biomass concentration in the presence of polyvinyl pyrrolidone onto weak anion exchangers.

Highlights

► β-galactosidase production from recombinant Saccharomices cerevicia ► cell lysate and adsorption onto Streamline-DEAE in an expanded bed. ► adsorption of target proteins from unclarified feedstock ► cell debris - matrix interaction, and the effect of polyvinyl pyrrolidone on the enzyme adsorption.

A Liquid Chromatography–Tandem Mass Spectrometric Method for Quantification of Curcumin-O-Glucuronide and Curcumin in Human Plasma

ScienceDirect Publication: Journal of Chromatography B — Sat, 26 May 2012 18:59:26 +0000

Publication year: 2012
Source:Journal of Chromatography B

Wei Chen, Patty Fan-Havard, Lisa D. Yee, Yu Cao, Gary D. Stoner, Kenneth K. Chan, Zhongfa Liu

Curcumin is a widely-used herbal medicine for various human diseases including inflammation and cancer. The demonstration and optimization of curcumin's activities in the clinical setting, however, has been compromised by its poor bioavailability and the lack of analytic methods to monitor its absorption. In this paper, we report the first validated liquid chromatography-tandem mass spectrometric method for simultaneous quantification of curcumin and its major metabolite: curcumin-O-glucuronide (COG), in the linear range of 2.0-2000ng/mL in human plasma. The intra-day and inter-day accuracies of curcumin and COG in human plasma were in the range of 91.3-111.5% and 82.7-109.2% and their co-efficiency of variations were in the range of 3.5-12.7% and 3.1-11.3%, respectively. This method was capable of detecting only COG in human plasma samples from two healthy volunteers after an oral ingestion of curcumin.

Highlights

► First direct method to measure curcumin-O-glucuronide (COG) in human plasma ► The LLOQ is 2ng/mL with CVs (<15%) and Accuracy (85% to 115%) ► Capable of characterizing the pharmacokinetics of COG up to 24 hr in human

Development of an oxidative dehydrogenation-based fluorescent probe for Cu2+ and its biological imaging in living cells

ScienceDirect Publication: Analytica Chimica Acta — Sat, 26 May 2012 15:56:50 +0000

Publication year: 2012
Source:Analytica Chimica Acta

Jiangli Fan, Xiaojian Liu, Mingming Hu, Hao Zhu, Fengling Song, Xiaojun Peng

Based on a boron dipyrromethene (BODIPY) derivative containing an N, O and S tridentate ligand, a Cu²⁺ fluorescent probe BTCu was developed. The detection mechanism was verified as Cu²⁺-promoted oxidative dehydrogenation of an amine moiety, leading to a formation of a fluorescent Cu⁺–Schiff base complex. Free BTCu exhibited a maximum absorption wavelength at 496nm, and a very weak maximum emission at 511nm. Upon addition of various metals ions, it showed large fluorescence enhancement toward Cu²⁺ (417-fold in MeCN and 103-fold in MeCN/HEPES solution, respectively) with high selectivity. The detection limits are as low as 1.74×10⁻⁸ M and 4.96×10⁻⁸ M in the two different solutions, respectively. And BTCu could work in a wide pH range with an extraordinary low pK a of 1.21±0.06. Using fluorescence microscopy, the probe was shown to be capable of penetrating into living cells and imaging intracellular Cu²⁺ changes.

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Graphical abstract Highlights

► The fluorescent probe contains an N, O and S tridentate ligand. ► The probe is simple but highly sensitive and selective towards Cu²⁺. ► The mechanism is based on the Cu²⁺-promoted dehydrogenation of amine in different organic and aqueous solutions. ► It was successfully applied to visualize Cu²⁺ in living cells.

Corona Discharge Ion Mobility Spectrometry with Orthogonal Acceleration Time of Flight Mass Spectrometry for Monitoring of Volatile Organic Compounds

Martin Sabo and Štefan Matejčík — Fri, 25 May 2012 17:37:55 +0000

Analytical Chemistry

DOI: 10.1021/ac300722s