Simultaneous separation of eight beta-adrenergic drugs using titanium dioxide nanoparticles as additive in capillary electrophoresis

The analysis is described for separating seven beta-adrenergic blocking agents (atenolol, celiprolol, clorprenaline, fenoterol, metoprolol, propranolol, terbutaline) and clenbuterol (sympathomimetic beta-2 receptor stimulating agonist, decongestant and bronchodilator, illicit anabolic used in athletics) by CE with UV detection. In order to simultaneously separate all analytes, Tris-H3PO4 solution was applied containing titanium dioxide nanoparticles (TiO2 NPs) as BGEs. The effects of important factors, such as concentration of TiO2 NPs, optimum pH, run buffer concentration, and separation voltage, were investigated so as to achieve best CE separation. The eight analytes could be well separated applying a separation voltage of 15 kV in 75 mM Tris-H3PO4 buffer at a pH of 2.40, containing 6.0 x 10(-6) g/mL TiO2 NPs. Under these optimal conditions, the RSDs for peak areas and for migration times were less than 2.7 and 2.3%, respectively. The detection limits were 0.1 microg/mL for celiprolol, 0.1 microg/mL for propranolol, 0.2 microg/mL for fenoterol, 1.0 microg/mL for atenolol, 1.0 microg/mL for clenbuterol, 1.0 microg/mL for clorprenaline, 1.0 microg/mL for metoprolol, and 1.0 microg/mL for terbutaline. The proposed method was successfully applied for the rapid CE determination of the frequently applied antihypertensive beta-blocking compounds atenolol, metoprolol, terbutaline, and propranolol in pharmaceutical tablets.     

Spectrofluorimetric and spectrophotometric determination of gliclazide in pharmaceuticals by derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole

Accurate, sensitive, and simple spectrophotometric and spectrofluorimetric methods were developed for the determination of gliclazide in pharmaceutical formulations and biological fluids. Both methods are based on a coupling reaction between gliclazide and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in borate buffer, pH 7.8, in which a yellow reaction product that can be measured spectrophotometrically at 400 nm was developed. The same product exhibited a yellow fluorescence at 470 nm upon excitation at 400 nm. The absorbance-concentration plot was rectilinear over the range of 2-20 microg/mL with minimum detectability [signal-to-noise (S/N) ratio = 2] of 0.2 microg/mL (6.18 x 10(-7) M); the fluorescence-concentration plot was rectilinear over the range of 0.2-2.5 microg/mL with minimum detectability (S/N = 2) of 0.02 microg/mL (6.18 x 10(-8) M). The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. Both methods were successfully applied to the analysis of commercial tablets. The results were in good agreement with those obtained with the official and reference spectrophotometric methods. A proposal of the reaction pathway was presented.     

Preparation and application of L-cysteine-modified CdSe/CdS core/shell nanocrystals as a novel fluorescence probe for detection of nucleic acid

The water-soluble L-cysteine-modified CdSe/CdS core/shell nanocrystals (expressed as CdSe/CdS/Cys nanocrystals) have been synthesized in aqueous by using L-cysteine as stabilizer. The size, shape, component and spectral property of CdSe/CdS/Cys nanocrystals were characterized by high-resolution transmission electron microscope (HRTEM), energy dispersive X-ray fluorescence (EDX), infrared spectrum (IR) and photoluminescence (PL). The results showed that the spherical CdSe/CdS/Cys nanocrystals with an average diameter of 2.3 nm have favorable fluorescent property, theirs photostability and fluorescence intensity are enhanced greatly after overcoating with CdS. The cysteine modified on the surface of core/shell CdSe/CdS nanocrystals renders the nanocrystals water-soluble and biocompatible. Based on the fluorescence quenching of the nanocrystals in the presence of calf thymus deoxyribonucleic acid (ct-DNA), a fluorescence quenching method has been developed for the determination of ct-DNA by using the nanocrystals as a novel fluorescence probe. The pH value of the system was selected at pH 7.4, with excitation and emission wavelength at 380 and 522 nm, respectively. Under the optimal conditions, the fluorescence quenching intensity of the system is linear with the concentration of ct-DNA in the range of 0.1-3.5 microg/mL (r=0.9987). The detection limit is 0.06 microg/mL. And two synthetic samples were analyzed satisfactorily.     

Amplified quenching of electrochemiluminescence from CdS sensitized TiO2 nanotubes by CdTe-carbon nanotube composite for detection of prostate protein antigen in serum

This work reports an ECL immunoassay method for ultrasensitive detection of prostate protein antigen (PSA), by remarkably efficient energy-transfer induced electrochemiluminescence (ECL) quenching from the CdS nanoparticles (NPs) sensitized TiO(2) nanotube array (CdS-TiO(2) NTs) to the activated CdTe NPs functionalized multi-wall carbon nanotubes (CdTe-MWNTs) composite. The coupling of TiO(2) and CdS NPs results in a cathodic ECL intensity 14.7 times stronger than that of the pure TiO(2) NTs electrode, which could be efficiently quenched by the CdTe-MWNTs. The enhanced mechanism of TiO(2) NTs ECL by CdS NPs was studied in detail by cyclic voltammetry and ECL spectroscopy. The strong absorption of the CdTe-MWNTs in the wavelength range of 400-800 nm renders them highly efficient for ECL quenching labeled on anti-PSA antibody. Based on a sandwich structure, we developed an ECL immunoassay method for the sensitive and selective detection of PSA. The ECL intensity decrement was logarithmically related to the concentration of the PSA in the range of 1.0 fg mL(-1) to 10 pg mL(-1) with a detection limit of 1 fg mL(-1). Human serum samples were then tested using the proposed immunoassay with excellent correlations, suggesting that the proposed immunoassay method is of great promise in clinical screening of cancer biomarkers.     

Colorimetric assay of propranolol tablets by derivatization: novel application of diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA)

A novel colorimetric assay of propranolol tablets has been developed. The assay is based on chemical derivatization (aromatic ring derivatization technique) using diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA) as the chromogenic derivatizing reagent and resultant formation of azo dyes. Optimization studies established an optimal reaction time of 5 min at 30 degrees C after mixing on a Vortex mixer the drug/reagent mixture for 10 s. A new absorption maximum (lambda(max)) was found at 470 nm, which was selected as the analytical wavelength. The assays were linear over 1-8 microg/mL propranolol, and the reaction occurred by a 1:1 reagent/drug stoichiometric ratio. The developed method has a low limit of detection of 0.76 microg/mL and is reproducible. It has been applied successfully to the assay of propranolol tablets and is of equivalent accuracy (p > 0.05) with the official (British Pharmacopoeia) ultraviolet spectrophotometric method. The new method has the main advantage of using more affordable instrumentation and could be applied to the in-process quality control of propranolol tablets.     

Sensitive spectrophotometric determination of nitrite in human saliva and rain water and of nitrogen dioxide in the atmosphere

A new simple, sensitive, and selective spectrophotometric method was developed for the determination of nitrite. The method is based on the reaction of nitrite with sulfathiazole in acidic medium to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride to form a highly stable, violet azo dye. The reaction product has an absorption maximum at 546 nm and obeys Beer's law over a nitrite range of 0.054-0.816 microg/mL. The molar absorptivity of the colored compound is 4.61 x 10(4) L/mol x cm). The detection limit is 12.1 microg/L. The relative standard deviation is 0.85% for 5 determinations of nitrite at 0.27 microg/mL. The reproducibility and validity of the proposed method are discussed in the present paper. The simplicity of the method is demonstrated by the high stability of the azo-dye product as well as the short time required for its complete formation in a reaction at room temperature without pH control or extra extraction. The sensitivity of the method is shown by the successful determination of nitrite in human saliva and rain water, and of nitrogen dioxide in the atmosphere. The results compare favorably with those obtained by the reference method. The selectivity of the method is indicated by its freedom from most interferences, even at high concentrations of nitrate (500 microg/mL).     

Application of functionalized CdS nanoparticles as fluorescence probe in the determination of nucleic acids

Nanometer-sized fluorescent particles were successfully synthesized. The nanoparticles have a narrow, tunable, symmetric emission spectrum and a broad, continuous excitation spectrum. They are also photochemically stable. A synchronous fluorescence method was developed for the rapid determination of DNA with functionalized CdS as a fluorescence probe, based on the synchronous fluorescence quenching of functionalized CdS in the presence of DNA. Maximum fluorescence is produced at pH 7.0, with maximum excitation and emission wavelengths of 360 and 620 nm, respectively. The maximum emission wavelength of synchronous fluorescence is 354 nm when delta lambda = 260 nm. Under optimum conditions, the calibration graphs are linear over the range 0-3.5 microg mL(-1) for calf thymus DNA (CT-DNA) and 0.2-3.0 microg mL(-1) for fish sperm DNA. The corresponding detection limit is 0.01 microg mL(-1) for CT-DNA and 0.02 microg mL(-1) for fish sperm DNA. The relative standard deviation of seven replicate measurements is 2.2% for 1 microg mL(-1) calf thymus DNA and 2.4% for 1 microg mL(-1) fish sperm DNA. The method is simple, rapid and sensitive. The recovery and relative standard deviation are very satisfactory.     

Microchip analysis of plant glucosinolates

We describe a new and selective analytical method for the separation and quantitation of plant glucosinolates. The new method, which utilizes microchip CE (micro-CE) with fluorescence detection, circumvents the multistep procedures characteristic of conventional methods. Glucosinolates form charge transfer complexes with the xanthene dyes phloxine-B and eosin-B. The glucosinolates-phloxine-B complex cannot be excited at 470 nm. Thus, the decrease in peak intensity of phloxine-B after complex formation is used to quantitatively measure total glucosinolates in Arabidopsis thaliana seeds. For qualitative analysis, complex formation with eosin-B is used. The sensitivity of eosin-B detection at excitation/emission 470 nm/540 nm was low. However, sensitivity increased following complex formation with sinigrin (> or =3 microg/mL). A batch-learning, self-organizing map was applied to visualize and organize analytical data into 2-D matrix with similar and related data clustered together or near each other. This organized matrix was used to optimize electrophoretic conditions for the analysis. This study suggests potential applications of micro-CE in plant metabolomics analyses without use of labeling fluorophores.     

Spectrophotometric determination of sulfur dioxide in air, using thymol blue

A simple and sensitive spectrophotometric method was developed for the determination of trace amounts of sulfur dioxide. The method is based on the reaction of SO2 with a known excess of ICI as the oxidant. The unreacted ICI iodinates thymol blue under acidic conditions. The lambdamax of thymol blue is at 545 nm under acidic conditions, and on lodination lambdamax shifts to 430 nm. This shift results in a decrease in the absorbance at 545 nm. The amount of uniodinated thymol blue present depends on the concentration of unreacted ICI, which in turn depends on the SO2 concentration. The system obeys Beer's law in the range 0-30 microg SO2 in a final volume of 25 mL, having a molar absorptivity of 3.2 x 10(4) L/mol cm with a relative standard deviation (RSD) of 2% at 24 microg SO2 (n = 10). The uniodinated dye can be extracted into 5 mL isoamyl alcohol under acidic conditions for measurement of absorbance. The extraction method obeys Beer's law in the range 0-5 microg SO2, having a molar absorpitivity of 4.16 x 10(4) L/mol x cm with an RSD of 1.9% at 4 microg SO2 (n = 10). The method has been successfully applied to the determination of atmospheric SO2.     

Determination of chlorine dioxide in water by gas chromatography-mass spectrometry

A sensitive gas chromatographic method has been established for the determination of chlorine dioxide in water. With weak basic conditions (pH 9.0), chlorine dioxide reacts with iodide to form iodine, which reacts with 2,6-dialkylphenol to form 4-iodo-2,6-dialkylphenol. The volatile organic derivative was extracted with ethyl acetate, and then measured by gas chromatography-mass spectrometry (GC-MS). The reaction of the active proton of 2,6-dialkylphenols (2,6-dimethylphenol, 2,6-di-isopropylphenol and 2,6-di-tert-butylphenol) with iodine was tested, and compared to each other in terms of reactivity and stability of the derivatives. 2,6-dimethylphenol showed rapid reaction with iodine, and its derivative was stable for 2 weeks. The detection limit of chlorine dioxide in water was about 1.0 ng/mL, and the calibration curve showed good linearity with r2 = 0.998. The existent concentration of chlorine dioxide in water was calculated from multiplying the concentration calculated from the calibration curve of 4-iodo-2,6-dimethylphenol by 0.544. The method was sensitive, reproducible and simple enough to permit the reliable analysis of chlorine dioxide at the low ng/mL level in water.     

Application of magdala red as a fluorescence probe in the determination of nucleic acids

A fluorescence quenching method was developed for the rapid determination of DNA and RNA using magdala red as fluorescence probe. In weakly acidic medium, the fluorescence of magdala red (lambdaex/lambdaem = 540/555 nm) can be largely quenched by DNA or RNA. The calibration graphs are linear over the range 0.01-1.2 microg/mL for both calf thymus DNA (CT DNA) and salmon DNA (SM DNA), and 0.015-1.0 microg/mL for yeast RNA, respectively. The corresponding detection limits are 6.0 ng/mL for CT DNA, 7.0 ng/mL for SM DNA and 15.0 ng/mL for yeast RNA, respectively. CT DNA could be determined in the presence of 20% (w/w) yeast RNA, and the relative standard deviation of six replicate measurements is 3.18% for 400 ng/mL of CT DNA. Interference from coexisting substances in the determination of DNA was also examined. Real samples were determined with satisfactory results.     

螯合微粒共振散射光谱分析测定痕量钴

研究了螯合微粒共振散射光谱的分析应用。结果表明,在pH为9．5的NH3-NH3Cl缓冲溶液中,Co（Ⅱ）与DDTC形成稳定的螯合物微粒体系,存在共振散射效应。在一定质量浓度范围内,Co（Ⅱ）的质量浓度与共振散射强度（IRS）呈较好的线性关系。其线性范围为0．012～1．44μg／mL,检出限为0．0012μg／mL,用于针剂维生素B12中钴的测定,方法简单、灵敏度高、重现性好,结果满意。     

Wavelength Dependence of the Fluorescence Quenching Efficiency of Nearby Dyes by Gold Nanoclusters and Nanoparticles: The Roles of Spectral Overlap and Particle Size

The efficiency of the glutathione monolayer-protected gold nanocluster (NC) Au(25) (1.2 nm metal core diameter (d)) in quenching the emission of dyes intercalated into DNA is compared to that of 2 and 4 nm gold nanoparticles (NPs). In all cases, the DNA/dye moieties and the gold particles are not covalently attached but rather form non-covalent ground state complexes. Under these conditions, steady-state measurements reveal that the quenching efficiency of Au(25) is a factor of 10 lower than that of plasmonic 4 nm gold NPs but comparable to that of 2 nm particles which do not show a distinct plasmon band. Nonetheless, significant emission quenching is observed even at very low (nM) concentrations of Au(25). The quenching efficiency of the 4 nm NPs is significantly higher for dyes emitting near the wavelength of the plasmon peak whereas that of the 2 nm gold NPs is well described by the nano-surface energy transfer (NSET) model proposed by the Strouse group (J. Am. Chem. Soc. 127, 3115 2005). Interestingly, for Au(25) the maximum quenching efficiency occurs for dyes emitting in the same wavelength range as that of the 2 and 4 nm NPs (490-560 nm), where it shows no discrete absorption features, rather than for wavelengths coincident with its HOMO-LUMO, intra-band or inter-band transitions. The fluorescence quenching properties of Au(25) NCs are therefore found to be distinct from those of larger NCs and NPs but do not appear to conform to theoretical predictions advanced thus far.     

Fluorescence quenching method for the determination of sodium carboxymethyl cellulose with acridine yellow or acridine orange

In near neutral to weak basic media, sodium carboxymethyl cellulose (NaCMC) will dissociate to become a macro polymeric anion, which can react with acridine yellow (AY) or acridine orange (AO) to form an ion-association complex resulting in fluorescence quenching of the acridine dyes. The maximum fluorescence quenching wavelength is 505 nm (lambda(ex)=440 nm) for AY system and 530 nm (lambda(ex)=493 nm) for AO system, respectively. The fluorescence quenching values (DeltaF) are directly proportional to the concentrations of NaCMC and the linear ranges are 20.0-4000 microg/L for AY system and 20.0-7000 microg/L for AO system, separately. This method has high sensitivity and the detection limits for NaCMC are 58.0 microg/L (AY system) and 157.2 microg/L (AO system). The effects of coexistent substance have been investigated, and the results show that this method has a relatively good selectivity. A fluorescence quenching method for the determination of NaCMC based on the ion-association reactions of CMC polymeric anion with a basic acridine dye was developed. The method is sensitive, simple and fast.     

卤代荧光素荧光猝灭法测定肾上腺色腙

在pH=6.6 的缓冲介质中, 肾上腺色腙(CBZC)与二氯荧光素(DCF)、二溴荧光素(DBF) 和二碘荧光素(DIF)通过静电引力、芳基堆积作用和范德华力形成摩尔比为2: 1的复合物, 引起上述二卤代荧光素的荧光发生猝灭, 最大猝灭波长分别位于533, 536和560 nm. 其荧光猝灭值(ΔF)在一定范围内与肾上腺色腙浓度成正比, 荧光猝灭反应具有较高的灵敏度, 对CBZC的检出限分别为3.3 ng/mL(CBZC-DCF体系), 5.7 ng/mL(CBZC-DBF体系)和129.6 ng/mL(CBZC-DIF体系). 考察了共存物质的影响、荧光猝灭反应的适宜条件和影响因素, 结果表明, 该方法具有良好的选择性, 可用于CBZC的血药和尿药浓度的快速检测. 从温度的影响、荧光寿命以及Stern-Volmer图判断该反应为静态猝灭反应.     

Facile synthesis of water-soluble and size-homogeneous cadmium selenide nanoparticles and their application as a long-wavelength fluorescent probe for detection of Hg(II) in aqueous solution

Highly luminescent uncoated water-soluble and mono-disperse CdSe nanoparticles (NPs) have been prepared facilely. Uncoated CdSe core NPs possessing a good size distribution was accompanied with long wavelength of fluorescence emission. It is interesting to note that these functionalized NPs are soluble in water medium stably for more than 1 month, and no significant changes were found in the optical characteristics in comparison with fresh CdSe NPs prepared. The functionalized CdSe NPs exhibited strong specific affinity for mercury(II) through their surface functional groups. Based on the significant quenching of fluorescence emission of functionalized CdSe NPs with a long-wavelength 630nm, a simple, rapid and specific detection for Hg(II) was proposed. Under optimum conditions, the response of linearly proportional to the concentration of Hg(II) is between 0mol/L and 1.25x10(-6)mol/L, and the limit of detection is 4.50x10(-9)mol/L. The relative standard deviation (R.S.D.) of six replicate measurements is 2.0% for 2.0x10(-7)mol/L of Hg(II). In terms of fluorescence quenching at 630nm of CdSe NPs, no obvious wavelength shift or no new emission band in presence of Hg(II) at pH 7.50 of phosphate buffer solution were found; furthermore, a significant reduction in absorbance at 230nm of CdSe NPs was first observed in our work. We could speculate that Hg(II) as an effective quencher (even at low concentration) for functionalized CdSe NPs emission suggests that it is capable of directly intercepting one of the charge carriers, thus disrupting the recombination process.     

Preparation of fluorescent polyvinyl alcohol keto-derivatives nanoparticles and selective determination of chromium(VI)

A novel fluorescent polyvinyl alcohol keto-derivatives nanoparticle (PVAK) has been prepared in one-step method. The nanoparticles has excitation and emission maxima at 349 and 462 nm, respectively. Based on the fluorescence quenching of PVAK by Cr(VI), we established a simple and selective fluorimetric method for the determination of Cr(VI) without separation of Cr(III) in water. The reaction conditions between Cr(VI) and PVAK were investigated in detail. Furthermore, the reaction mechanism between PVAK and Cr(VI) was also discussed. Under optimal experimental conditions, a limit of detection of 0.02 microg mL(-1) was achieved. The calibration curve was linear over the concentration range 0.1-13.2 microg mL(-1) with a correlation coefficient of 0.9987. The proposed method has been applied to the selective quantification of Cr(VI) in synthetic samples and waste-water samples with the satisfactory results.     

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

Fluorometric Determination of Iron(Iii) with O-Hydroxyhydroquinonephthalein in the Presence of Brij 58

Abstract

A highly sensitive fluorescence reaction of iron(III) with o-hydroxyhydroquinonephthalein (Qnph) in the presence of various surfactants, and its application to the fluorophotometry of trace amounts of iron(III) is described. the method is based on the fluorescence quenching reaction between Qnph and iron(III) in the presence of Brij 58 at pH 3–4. the quenching calibration graph was linear over the range 0 – 300 ng per ml iron(III) by using fluorescence reaction at Em 525 nm with Ex 470 nm, and the iron(III) detection limit was 5 ng/ml. the proposed method is simple, rapid and does not involve heating or solvent extraction.     

基于PbS QDs/TiO2 NPs构建新型谷胱甘肽光电化学传感器

通过高温煅烧将二氧化钛纳米颗粒(TiO₂ NPs)修饰到ITO电极表面制成TiO₂ NPs/ITO电极, 再采用连续离子层吸附反应(SILAR)循环将硫化铅量子点(PbS QDs)修饰到TiO₂/ITO电极表面制得PbS QDs/TiO₂ NPs/ITO电极, 并将该电极应用于检测谷胱甘肽(GSH)的光电化学传感器. 在该传感器中, 当PbS QDs受470 nm可见光的激发时将产生电子(e)和光生空穴(h ⁺), 光生空穴可被溶液中的GSH捕获, 并将GSH氧化成GSSH, 有效避免电子和空穴的复合, 显著提高了光电效率. 该传感器对GSH的检测具有较高的灵敏度和选择性, 线性检测范围为0.06~1 mmol/L, 检出限(LOD)为4.6×10 ^-3 mmol/L(S/N=3).