Determination of amlodipine using terbium‐sensitized luminescence in the presence of europium(III) as a co‐luminescence reagent

A sensitive time‐resolved luminescence method for the determination of amlodipine (AM) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of terbium (Tb³⁺) by formation of a ternary complex with AM in the presence of tri‐n‐octylphosphine oxide (TOPO) as co‐ligand, dodecylbenzenesulfate as surfactant and europium ion as a co‐luminescence reagent. The signal for Tb–AM–TOPO is monitored at λ_ex = 242 nm and λ_em = 550 nm. Optimum conditions for the formation of the complex in aqueous system were 0.015 m Tris (hydroxylmethyl) amino methane buffer, pH 9.0, TOPO (1.0 × 10^–4 m ), Eu³⁺ (2.0 × 10^–7 m ), dodecylbenzenesulfate (0.14%) and 6.0 × 10^–5 m of Tb³⁺, which allows the determination of 10–50 ppb of AM with a limit of detection of 1.2 ppb. The relative standard deviations of the method range between 0.1 and 0.2% indicated excellent reproducibility of the method. The proposed method was successfully applied for the assay of AM in pharmaceutical formulations and in plasma samples. Average recoveries of 98.5 ± 0.2% and 95.2 ± 0.2% were obtained for AM in tablet and plasma samples respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectrofluorimetric determination of dopamine using 1,5-bis(4,6-dicholro-1,3,5-triazinylamino) naphthalene.

A new fluorescent reagent, 1,5-bis(4,6-dichloro-1,3,5-triazinylamino)naphthalene, containing two active chlorines, was synthesized by a one-step reaction. Under the optimum conditions for the determination of dopamine, the enhanced fluorescence intensity is proportional to the dopamine concentration. The fluorescence intensity was measured at lambda(ex/em) = 400/460 nm, with and without dopamine. The linear range and detection limit for the determination of dopamine were 1.0 x 10(-7) mol/L-5.0 x 10(-5) mol/L and 4.0 x 10(-8) mol/L. This method is simple, practical, can afford good precision and accuracy and can be successfully applied to assess dopamine in injections and human serum samples.     

Flow injection spectrophotometric determination of the antibiotic fosfomycin in pharmaceutical products and urine samples after on-line thermal-induced digestion

A new flow injection (FI) method for the precise and rapid spectrophotometric determination of the antibiotic fosfomycin (FMC) in urine and pharmaceutical samples is described. The method is based on the on-line quantitative thermal-induced digestion of the analyte prior to injection into the FI system. Ammonium persulfate was used as the oxidation reagent. The resulting orthophosphate ions were determined spectrophotometrically (lambda(max) = 690 nm) using the molybdenum blue approach. Chemical and FI variables that affected on-line oxidation were studied and optimized. The proposed method is very precise (s(r) = 1.2% at 1.0 x 10(-4) mol L(-1) FMC, n = 12), offers a high sampling rate of 60 h(-1), and allows for the determination of the analyte in the range 3.0 x 10(-6) to 3.0 x 10(-4) mol L(-1) with a satisfactory 3sigma detection limit of 1.0 x 10(-6) mol L(-1). Application of the proposed method to urine and pharmaceutical samples yielded accurate results with percentage recoveries in the range 96.4-102.5%.     

Determination of atenolol by the micelle-stabilized room-temperature phosphorescence methodology.

A micellar-stabilized room-temperature phosphorescence (MS-RTP) method for the determination of atenolol has been developed in micellar solutions of sodium dodecylsulphate (SDS) in the presence of thallium(I) as a heavy atom and sodium sulphite as an oxygen scavenger. The effects of thallium(I) nitrate, SDS and sodium sulphite concentrations on atenolol MS-RTP intensity were studied. Optimized conditions to obtain maximum sensitivity were 0.015 mol/L thallium(I) nitrate, 0.1 mol/L SDS and 0.0075 mol/L sodium sulphite. The maximum phosphorescence signal was completely developed in 10 min and the intensity was measured at lambda(ex) = 272 nm and lambda(em) = 412 nm. The linear range of application obtained was 2.01-16.00 microg/mL. The detection limit estimated from the least-squares regression analysis was 0.86 microg/mL and the relative standard deviation of 10 replicates was 1.7%. The proposed method was applied to the determination of atenolol in a pharmaceutical formulation. The quantitation was carried out by means of standard calibration, standard-additions calibration and Youden calibration. These three experiments were necessary to evaluate the presence of constant and proportional errors due to the matrix.     

Chemiluminescence determination of fluoroquinolone antibiotics using a soluble manganese (IV)-sulphite system.

The reaction of soluble manganese (IV) with sulphite in acidic condition was found to elicit weak chemiluminescence (CL). The CL signal was remarkably enhanced in the presence of three fluoroquinolones, viz. norfloxacin, ofloxacin and ciprofloxacin. Based on these observations, a new flow-injection CL method was developed for the determination of these fluoroquinolones. The method allows determination in the range 5.0 x 10(-8)-1.0 x 10(-6) mol/L for norfloxacin, 1.0 x 10(-7)-8.0 x 10(-6) mol/L for ofloxacin and 1.0 x 10(-7)-3.0 x 10(-5) mol/L for ciprofloxacin, with detection limits of 3 x 10(-8) mol/L, 5 x 10(-8) mol/L and 3 x 10(-8) mol/L, respectively. The method was applied to the determination of fluoroquinolones in pharmaceutical preparations.     

Spectrofluorimetric determination of 5-hydroxytryptamine using chlorosulphonylthenoyltrifluoroacetone-europium probe.

A new spectrofluorimetric method was developed for the determination of trace amounts of 5-hydroxytryptamine (5-HT). Using chlorosulphonylthenoyltrifluoroacetone (CTTA)-europium (Eu(3+)) ion as a fluorescent probe in a buffer solution at pH 11.0, 5-HT can remarkably enhance the fluorescence intensity of the CTTA-Eu(3+) complex at lambda = 612 nm; the enhanced fluorescence intensity of Eu(3+) is proportional to the concentration of 5-HT. Optimum conditions for the determination of 5-HT were also investigated. The linear range and detection limit for the determination of 5-HT were 1.0 x 10(-7)-1.2 x 10(-5) mol/L and 8.5 x 10(-8) mol/L, respectively. This method is simple, practical and relatively free of interference from coexisting substances, and can be applied to assess 5-HT in urine samples.     

Spectrophotometric determination of carbinoxamine maleate in pharmaceutical formulations by ternary complex formation with Cu(II) and eosin

A simple and sensitive spectrophotometric method was developed for the determination of carbinoxamine maleate in pharmaceutical formulations. The method is based on the formation of a ternary complex, extractable with chloroform, between copper(II), eosin, and carbinoxamine maleate. The absorption spectra of the ternary complexes shows, under optimum conditions, a maxima at 538 nm, with apparent molar absorptive 6.1690 x 10(4) mol(-1) cm(-1), Sandell's sensitives 6.75 x 10(-3) microg cm(-2), and linearity in the concentration range 0.75-10.0 microg ml(-1). The method can be achieved with high accuracy (recovery values, 100 +/- 2%) and precision (with standard deviation 0.029-0.155 and relative standard deviation 3.87-1.55%). The method was again successfully applied, with high accuracy and good precision, for the determination of carbinoxamine maleate in various pharmaceutical formulations (syrup, drops, and tablets).     

Gold nanoparticles‐based fluorescence enhancement of the terbium–levofloxacin system and its application in pharmaceutical preparations

A sensitive fluorescence (FL) technique is proposed for the determination of levofloxacin (LVX). The method is based on the fact that the weak FL signal of the Tb(III)–LVX system is strongly enhanced in the presence of gold nanoparticles. Gold nanoparticles were prepared by the citrate reduction of HAuCl₄ and characterized by transmission electron microscopy (TEM). Levofloxacin and Tb(III) ion form a fluorescence complex in aqueous solution, and its maximum emission wavelength was found at 545 nm. Optimal conditions for the formation of the levofloxacin–Tb(III) complexes were studied. Levofloxacin was detected by measuring the FL intensity, which increases linearly with the concentration of LVX in the range 6.2 × 10⁻¹⁰–2.6 × 10⁻⁸ mol/L. Recovery of the target analytes was > 96% with good quality parameters: linearity (r² > 0.996), limit of detection (LOD) and limit of quantification (LOQ) values 2.1 × 10⁻¹⁰ mol/L and 7.2 × 10⁻¹⁰ mol/L, and run‐to‐run and day‐to‐day precisions with relative standard deviations (RSDs) around 3%. Thus, the proposed method can be successfully applied to the routine determination of levofloxacin in pharmaceutical preparations. Copyright © 2011 John Wiley & Sons, Ltd.     

A homogeneous DNA hybridization system by using a new luminescence terbium chelate

Homogeneous DNA hybridization assay based on the luminescence resonance energy transfer (LRET) from a new luminescence terbium chelate, N,N,N(1),N(1)-[2,6-bis(3'-aminomethyl-1'-pyrazolyl)-4-phenylpyridine]tetrakis(acetic acid) (BPTA)-Tb(3+) (lambda(ex) = 325 nm and lambda(em) = 545 nm) to an organic dye, Cy3 (lambda(ex) = 548 nm and lambda(em) = 565 nm), has been developed. In the system, two DNA probes whose sequences are complementary to the two different consecutive sequences of a target DNA are used; one of the probes is labeled with the Tb(3+) chelate at the 3'-end, and the other is with Cy3 at the 5'-end. Labeling of the Tb(3+) chelate is accomplished via the linkage of a biotin-labeled DNA probe with the Tb(3+) chelate-labeled streptavidin. Strong sensitized emission of Cy3 was observed upon excitation of the Tb(3+) chelate at 325 nm, when the two probe DNAs were hybridized with the target DNA. The sensitivity of the assay was very high compared with those of the previous homogeneous-format assays using the conventional organic dyes; the detection limit of the present assay is about 30 pM of the target DNA strand.     

Determination of norfloxacin using a terbium-sensitized electrogenerated chemiluminescence method.

A simple electrogenerated chemiluminescence (ECL) analysis method for the determination of norfloxacin (NFLX) is reported. It is based on ECL produced by Na(2)SO(3), which is sensitized by the Tb-NFLX complex. The relative ECL intensity of the Tb(3+)-NFLX-Na(2)SO(3) system is proportional to the amount of NFLX. The optimized experimental conditions were investigated. The linear range and detection limit for NFLX were 1.0 x 10(-10)-8.0 x 10(-7) mol/L and 2.8 x 10(-11) mol/L, respectively. This method was successfully applied to the determination of NFLX in a capsule. NFLX in urine can be directly detected without pretreatment or separation.     

Interactions of the DNA intercalator acridine orange, with itself, with caffeine, and with double stranded DNA

Caffeine (CAF) inhibits the intercalation of acridine orange (AO) into cellular DNA. Optical absorption and fluorescence spectroscopy were employed to determine the molecular interactions of AO with itself, with CAF, and with double stranded herring sperm DNA (dsDNA). AO dimerization was observed at concentrations >2 micromol. The sharp increase in fluorescence (lambda(em)=530 nm) at 5 micromol of AO was attributed to AO multimer formation. From 0.5 to 5.0 micromol, the AO self-association binding constant (K(assoc)) was determined to be 38620 mol(-1), however, the presence of 150 mmol NaCl increased K(assoc) to 118000 mol(-1) attributed to the charge neutralization. The K(assoc) for AO with CAF was confirmed to be 256 mol(-1). K(assoc) for the binding of AO with 20 micromol DNA ranged from, 32000 mol(-1) at 2 micromol AO, to approximately 3700 mol(-1) at 10 micromol AO, in the absence of NaCl. This AO concentration dependency of K(assoc) value with DNA was attributed to AO intercalation into dsDNA at high dsDNA/AO ratios, and electrostatic binding of AO to dsDNA at low AO ratios. The findings provide information used to explain fluorescence intensity values at lambda(em) at 530 nm from studies that combine AO, caffeine, and dsDNA.     

Investigation on the co‐luminescence effect of europium (III)–lanthanum(III)–dopamine–sodium dodecylbenzene sulfonate system and its application

A novel luminescence, enhancement phenomenon in the europium(III)–dopamine–sodium dodecylbenzene sulfonate system was observed when lanthanum(III) was added. Based on this, a sensitive co‐luminescence method was established for the determination of dopamine. The luminescence signal for the europium (III)–lanthanum(III)–dopamine–sodium dodecylbenzene sulfonate system was monitored at λ_ex = 300 nm, λ_em =618 nm and pH 8.3. Under optimized conditions, the enhanced luminescence signal responded linearly to the concentration of dopamine in the range 1.0 × 10^–10–5.0 × 10^–7 mol/L with a correlation coefficient of 0.9993 (n = 11). The detection limit (3σ) was 2.7 × 10^–11 mol/L and the relative standard deviation for 11 parallel measurements of 3.0 × 10^–8 mol/L dopamine was 1.9%. The presented method was successfully applied for the estimation of dopamine in samples of pharmaceutical preparations, human serum and urine. The possible luminescence enhancement mechanism of the system is discussed briefly. Copyright © 2013 John Wiley & Sons, Ltd.     

普通小球藻引发水中17β-雌二醇的光降解

研究了普通小球藻引发水中17β-雌二醇(E2)的光降解,结果表明,在250W高压汞灯(HPML,nm)的照射下,藻浓度为4．0×10^10个·L^-1时,17β-雌二醇的光降解率可达37％．藻浓度为4．2×10^10个·L^-1时,17β-雌二醇浓度在1．5×10^-5-6．0×10^-5mol·L^-1范围内,其光降解速率与初始浓度成正比,反应是假一级．另外,还研究光强、藻悬浮液浓度和17β-雌二醇初始浓度等对此反应体系的影响。     

An improved HPLC assay with fluorescence detection for the determination of domperidone and three major metabolites for application to in vitro drug metabolism studies

Domperidone is currently used in Canada and Europe for the treatment of intestinal motility disorders as well as for its antiemetic properties. Recent drug metabolism studies have indicated that domperidone is a substrate of different subtypes of CYP3A family and consequently, the drug requires complete characterization of its metabolism for the identification of major drug-drug interactions. Therefore, the purpose of our studies was to develop a simple, sensitive and rapid HPLC assay for the determination of domperidone and its major metabolites. This assay had to be suitable for the conduct of in vitro drug metabolism study with human liver microsomes. Baseline resolution of internal standard, domperidone and three of its major metabolites was achieved in a run time of less than 15 min using an Ultrasphere ODS column (250 mm x 4.6 mm x 5 microM) and a mobile phase consisting of disodium citrate buffer (10 mM, pH 3.4):methanol:acetonitrile:trietylamine, 54.6:34.7:9.9:0.8 at a flow rate of 1.0 mL/min. Chromatographic separation was executed at room temperature. Quantification was performed by tandem fluorescence (excitation lambda=282 nm and emission lambda=328 nm) and ultraviolet detectors (lambda=254 nm for the quantification of encainide, internal standard). Calibration curves were constructed and showed linearity in the range of 0.1-20 micromol/L and 10-250 micromol/L. Intra- and interday coefficients of variation were less than 8% and 11%, respectively. Mean accuracy was 100.5+/-9.9% and limit of quantification was established at 0.06 micromol/L for domperidone and its metabolites. The assay allows estimation of enzymatic parameters (K(m) and V(max)) of domperidone for the formation of its various metabolites and sensitivity is sufficient for the conduct of inhibition studies with potent CYP3A inhibitors.     

Multicommutated flow-through optosensors implemented with photochemically induced fluorescence: determination of flufenamic acid

This article describes a multicommutated flow injection-solid phase spectroscopy system implemented with photochemically induced fluorescence for the determination of flufenamic acid (FFA). A strongly fluorescent photoproduct is generated when FFA is irradiated online under UV light in a strong sulfuric medium. The photoproduct generated is retained on C(18) silica gel (which fills the detection area of the flow cell) and directly monitored on the active solid support at 258/442 nm (lambda(ex)/lambda(em)). After maximum signal recording, the sensing zone is regenerated by eluting the retained photoproduct with an appropriate H(2)SO(4)/MeOH solution. The sensor, completely automated, is based on the use of three-way solenoid valves conveniently operated by a homemade multicommutation software written in Java language. The system is calibrated at 10 and 60s for sampling time, showing detection limits of 1.28 x 10(-9) and 5.33 x 10(-10) molL(-1) and sampling rates of 38 and 28 h(-1), respectively, with relative standard deviations of 0.9 and 1.2%. The applicability of the method is demonstrated for the determination of FFA in human serum, human urine, and a pharmaceutical preparation without any pre-treatment. Good recovery levels were achieved between 90.5 and 103.7%.     

Determination of bisphenol A using a flow injection inhibitory chemiluminescence method.

A new flow injection chemiluminescence (CL) method has been developed for the determination of bisphenol A (BPA), based on the inhibitory effect of BPA on the chemiluminescence reaction between luminol and potassium hexacyanoferrate. Under optimum conditions, the decrease in CL emission intensity was linear with BPA concentration in the range 8.0 x 10(-7)-1.2 x 10(-5) mol/L, and the detection limit was 3.1 x 10(-7) mol/L. The relative standard deviation (RSD) of 11 replicate measurements was 2.6% for 2.0 x 10(-6) mol/L BPA (n = 11). The sampling frequency was calculated to be ca. 120/h. This method has been successfully used to determine the content of BPA in aqueous solution of polycarbonate materials. A brief discussion on the possible chemiluminescence reaction mechanism is presented.     

Determination of trace alkaline phosphatase by solid-substrate room-temperature phosphorimetry based on Triticum vulgare lectin labeled with fullerenol

Fullerenol (F) shows a strong and stable room-temperature phosphorescence (RTP) signal on the surface of nitrocellulose membrane (NCM) at lambda ex max/ lambda em max =542.0/709.4 nm. When modified by dodecylbenzenesulfonic acid sodium salt (DBS), fullerenol emits a stronger signal. It was also found that quantitative specific affinity-adsorption reaction can be carried out between Triticum vulgare lectin (WGA) labeled with DBS-F and alkaline phosphatase (ALP) on the surface of NCM, and the product obtained (WGA-ALP-WGA-F-DBS) emits a strong and stable RTP signal. Furthermore, the content of ALP was proportional to the DeltaI(p) value. Based on the facts above, a new method for the determination of trace amounts of ALP by affinity-adsorption solid-substrate room-temperature phosphorimetry (AA-SS-RTP) was established, using fullerenol modified with DBS to label WGA. The detection limit was 0.011 fg spot(-1) (corresponding concentration: 2.8x10(-14) g ml(-1), namely 2.8x10(-16) mol l(-1)). This method with high sensitivity, accuracy, and precision has been successfully applied to the determination of the content of ALP in human serum survey and forecast human disease, and the results are tallied with those using alkaline phosphatase kits. The mechanism for the determination of ALP using AA-SS-RTP was also discussed.     

Determination of tetracycline, chlortetracycline and oxytetracycline by flow injection with inhibitory chemiluminescence detection using copper(II) as a probe ion.

This paper reports an indirect flow-injection (FI) method for the determination of the tetracycline drugs (TCs), tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC), using copper(II) as a probe ion. The method was based on the inhibition caused by these TCs to the copper(II)-catalysed chemiluminescence (CL) reaction between luminol and H(2)O(2). The CL reaction was induced on-line and injection of the sample produced negative peaks as a result of the copper(II) complexation or displacement by the analytes. The height of the peaks was proportional to the drug concentration in the sample. The choice of the catalyst ion, the concentration of luminol, H(2)O(2) and copper(II) are discussed. The linear range was 3.6 x 10(-8)-1.0 x 10(-5), 1.1 x 10(-7)-1.0 x 10(-5) and 1.9 x 10(-7)-1.0 x 10(-5) mol/L for TC, CTC and OTC, respectively. The detection limit was 5.0 x 10(-9) mol/L for TC, 1.0 x 10(-8) mol/L for CTC and 2.0 x 10(-8) mol/L for OTC (3sigma), respectively. The method was applied to the determination of TCs in pharmaceutical preparations and human urine with recoveries in the range 95-105%.     

Application of a lanthanide composite nanoparticle‐sensitized luminescence method for the determination of salicylic acid in pharmaceutical formulations and human plasma

Terbium‐acetylacetone (Tb–acac) composite nanoparticles were synthesized using the ultrasonic method. The nanoparticles are water‐soluble, stable and have extremely narrow emission bands and high internal quantum efficiencies. They were used as fluorimetric probes in the determination of salicylic acid (SA), based on the fluorescence enhancement of nanoparticles through fluorescence resonance energy transfer (FRET). The influence of buffer solution was investigated. Under the optimum conditions, a linear calibration graph was obtained over the SA concentration range 5 × 10^–7–1 × 10^–4 mol/L. The limit of detection was found to be 2.5 × 10^–8 mol/L. The relative standard deviation (RSD) for six repeated measurements of 1 × 10^–4 mol/LSA was 1.75%. The method was applied to the determination of SA in pharmaceutical formulations and human plasma. We believe that the proposed approach has great potential for clinical purposes. Copyright © 2008 John Wiley & Sons, Ltd.     

Luminescent complexes of terbium ion for molecular recognition of ibuprofen

The complexation behavior and luminescent properties of terbium (Tb³⁺) complexes containing bi‐dental ligands were studied: nitrogen – 1,10‐phenanthroline, and oxygen – trifluoroacetylacetone as well as acetylacetone ligands with ibuprofen (Ibu; a non‐steroidal anti‐inflammatory drug). Aqueous and aqueous alcohol microheterogeneous solutions were used as media. The effects of solubilization by various micellar solutions, pH and ligand type on luminescent properties of Tb³⁺ complexes were investigated. Sensitized luminescence of mixed ligand complex Tb(1,10‐phenanthroline)‐Ibu and dynamic quenching effect in complex Tb(trifluoroacetylacetone)₃‐Ibu allow Ibu determination with the limit of detection 5.3 × 10^–8 mol/L and 1.26 × 10^–6 mol/L, respectively. Copyright © 2013 John Wiley & Sons, Ltd.