Spectrophotometric Determination of Furosemide Based on Its Complexation with Fe(III) in Ethanolic Medium Using a Flow Injection Procedure

Abstract

A fast flow injection procedure with spectrophotometric detection based on the furosemide complexation with Fe(III) ions in ethanolic media is described. As carrier the flow single line system configuration used an ethanolic 10^?2 mol L^?1 Fe(III) solution flowing at 1.0 mL min^?1, a 50 cm sample loop (250 µL total sample injection), and a 50 cm long reactor coil, at room temperature. The detection at 513 nm presented a linear dynamic range from 1.00×10^?4 to 1.00×10^?2 mol L^?1, obeying the linear equation Abs=8.9×10^?3+22.3×[furosemide] (r=0.998, n=7). The limit of detection (3σ/slope) was 3.00×10^?5 mol L^?1. The proposed method was applied to four commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte without an effect from the other substances present in the formulation. The proposed procedure presented an analytical frequency of 95 measurements per hour. The results agreed with those from both the label and those determined by a spectrophotometric comparative procedure. Recoveries close to 100% were found in the commercial formulations and synthetic urine matrixes.     

Cloud-point extraction,preconcentration, and spectrophotometric determination of palladium in water samples

The possibility of using Thio-Michler's Ketone (TMK), 4,4′-bis(dimethylamino) thiobenzophenone, for palladium(II) concentrated by micellar extraction at the cloud-point temperature, and later spectrophotometric determination, was investigated. Under the optimum conditions, preconcentration of 50?mL of water samples in the presence of 0.1% (w/v) octylphenoxy polyethoxy ethanol (Triton X-114), 2?×?10^?6?mol?L^?1?TMK and 1?×?10^–3?mol?L^?1 buffer solution (pH?=?3.0) gave the limit of detection of 0.47?ng?mL^?1, and the calibration graph was linear in the range of 2–50?ng?mL^–1. The recovery under optimum working conditions was higher than 97%. The proposed method has been applied to the spectrophotometric determination of palladium(II) in natural water samples after cloud-point extraction with satisfactory results.     

Adsorptive stripping voltammetry of nickel at a bare glassy carbon electrode

A bare glassy carbon electrode is applied to nickel determination by adsorptive stripping voltammetry in the presence of dimethylglyoxime as a complexing agent. A procedure of nickel determination and electrode regeneration was proposed. The calibration graph for Ni(II) for an accumulation time of 120?s was linear from 2?×?10^?9 to 1?×?10^?7?mol?L^?1. The detection limit was 8.2?×?10^?10?mol?L^?1. The relative standard deviation for a solution containing 2?×?10^?8?mol?L^?1 of Ni(II) was 4.1%. The proposed procedure was applied for Ni(II) determination in certified water reference materials.     

Application of simultaneous separation and derivatization for the determination of α‐lipoic acid in urine samples by high‐performance liquid chromatography with spectrofluorimetric detection

To help to clarify therapeutic functions of lipoic acid (LA) in biochemical and clinical practice we have elaborated a fast, simple and accurate HPLC method enabling determination of LA in human urine. The proposed analytical approach includes reduction of LA with tris(2‐carboxyethyl)phosphine and simultaneous separation and derivatization of the analyte with butylamine and o‐phthaldialdehyde followed by spectrofluorimetric detection at λ_ex = 340 nm and λ_em = 440 nm. The assay was performed using gradient elution and the mobile phase containing 0.0025 mol L^?1 o‐phthaldialdehyde in 0.0025 mol L^?1 NaOH and acetonitrile. Linearity of the detector response for LA was observed in the range of 0.3–8 μmol L^?1. Limits of detection and quantification for LA in urine samples were 0.02 and 0.03 μmol L^?1, respectively. The total analysis time, including sample work‐up, was <20 min. The analytical procedure was successfully applied to analysis of real urine samples delivered from six healthy volunteers who received a single 100 mg dose of LA.     

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron‐Doped Diamond Electrode

A cathodically pretreated boron‐doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry. Linear calibration curves (r=0.999) were obtained from 1.9×10^?5 to 2.1×10^?4 mol L^?1 for AA and from 9.7×10^?6 to 1.1×10^?4 mol L^?1 for CAF, with detection limits of 19 μmol L^?1 and 7.0 μmol L^?1, respectively. This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations, with results equal to those obtained using a HPLC reference method.     

Spectrophotometric Multicommutated Flow System for the Determination of Hypochlorite in Bleaching Products

Abstract

A multicommutation flow system for the spectrophotometric determination of hypochlorite in bleaching products is proposed. In this system, N,N-diethyl-p-phenylenediamine (DPD) reacts with hypochlorite, and the product was monitored at 515 nm. The analytical curve for hypochlorite was linear in the concentration range from 2.68 × 10^?5 to 1.88 × 10^?4 mol L^?1 (2–14 mg L^?1) with a detection limit of 6.84 × 10^?6 mol L^?1 (0.51 mg L^?1). The sampling rate was 45 h^?1, and a relative standard deviation of 1.4% (n = 10) was obtained. The recovery of this analyte ranged from 97.2% to 102.5%, and the results found using the proposed spectrophotometric multicommutated flow system agreed with the data obtained using a reference method (iodometric titration) at the 95% confidence level.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Kinetic Spectrophotometric Determination of Thiols and Ascorbic Acid

Abstract

This paper describes a kinetic spectrophotometric method for the determination of L‐ascorbic acid (AA) and thiols (RSH). Absorbance of Fe(II)‐phen complex formed during the reaction of AA or RSH with Fe(III)‐phen was continuously measured at 510 nm by double‐beam spectrophotometer with flow cell. For determination some thiols, the catalytic effect of Cu²⁺ ions was used. AA and RSH can be determined in concentration ranges from 4.0×10^?6 to 4.0×10^?5 M and from 8.0×10^?6 to 8.0×10^?5 M, respectively. The applicability of the proposed method was demonstrated by determination of chosen compounds in pharmaceutical dosage forms.     

Kinetic Determination of Uric Acid in Human Serum by Using the Uncatalyzed BZ Reaction in Non‐equilibrium Steady State

A novel kinetic method for determination of uric acid in human serum by means of an uncatalyzed BZ system consisting of potassium bromate and p‐hydroxybenzaldehyde (p‐HBA) in sulfuric acid medium was proposed, in which the analyte perturbation to the system was recorded close to the bifurcation point. The potential change was directly proportional to the logarithm of concentration of uric acid in the range of 3.73×10^?8–7.48×10^?4 mol·L^?1 (r=0.9983) with a detection limit of 7.45×10^?9 mol·L^?1 and a recovery from 98.9% to 101.1%. A comparison between the proposed technique and other methods indicated that results obtained were in agreement with those in clinical detection. In addition, the possible mechanism of action of uric acid on the uncatalyzed BZ reaction was also discussed briefly.     

Determination of lipoic acid, Trolox methyl ether and tocopherols in human plasma by liquid-chromatography and ion-trap tandem mass spectrometry

A method for the simultaneous determination of lipoic acid and/or Trolox methyl ether, along with α‐, γ‐ and δ‐tocopherol was developed using liquid chromatography–tandem mass spectrometry with negative electrospray ionization (HPLC‐ESI‐MS/MS) in an ion‐trap mass spectrometer. Detection and quantification were accomplished by a multiple reaction monitoring method, using specific transitions from precursor ion to product ion for each analyte. Chromatographic separation was achieved in a 12 min run using a C₁₈‐bonded phase and methanol–aqueous ammonium acetate elution gradient. Linear correlations of the chromatographic peak area (r.u. × s^?1) to the injected amount (ng) gave the slope values (r.u. × s^?1 × ng^?1) 2.34 × 10⁴ for α‐tocopherol, 5.05 × 10⁴ for γ‐tocopherol, 1.27 × 10⁵ for δ‐tocopherol, 8.86 × 10⁵ for lipoic acid and 1.23 × 10⁵ for Trolox methyl ether. The lower limit of quantification ranged between 0.02 and 1.22 ng for Trolox methyl ether and lipoic acid. MS³ experiments of γ‐ and δ‐tocopherol suggest ion‐radical reactions and dependence of the tocopherol fragmentation pattern on the phenolic ring methylation degree. The method is shown to be applicable to measurement of these metabolites in human serum after extraction. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of Mefenamic Acid and Paracetamol by First Derivative Spectrophotometry

Abstract

A direct and simple first derivative spectrophotometric method has been developed for the determination of mefenamic acid and paracetamol in pharmaceutical formulations. A methanolic hydrochloric acid solution was used as solvent for extracting the drugs from the formulations and subsequently the samples were evaluated directly by derivative spectrophotometry. Simultaneous determination of both drugs can be carried out using the zero-crossing and the graphical methods. The methods do not require simultaneous equations to be solved. The calibration graphs were linear in the ranges from 1.8 × 10^?6 to 1.6 × 10^?4 M of mefenamic acid and from 4.1×10^?6 to 1.4 × 10^?4 M of paracetamol. The ingredients commonly found in commercial pharmaceutical formulations do not interfere. The proposed method was applied to the determination of these drugs in tablets.     

Determination of trace amounts of chromium (VI) by flow injection analysis with chemiluminescence detection

A new sensitive chemiluminescence (CL) method combined with continuous flow injection analysis is described for the determination of Cr(VI). Strong CL signals were generated by Cr(VI)-catalysed oxidation of gallic acid in the presence of potassium permanganate and hydrogen peroxide. Effects of reagent concentrations, temperature, pH, flow rates, mixing coil length and mixing flow sequences on the chemiluminescence intensity were studied. Under the optimised experimental conditions, the relationship between the logarithm of concentration (log?C) of Cr(VI) and the logarithm of intensity (log?I) is linear over the range of 2?×?10^?11 – 5?×?10^?4?mol?L^?1, with the detection limit (3σ) of 4?×?10^?12?mol?L^?1. Relative standard deviation of ten measurements of 1?×?10^?9?mol?L^?1 Cr(VI) is 1.7%. This flow injection analysis (FIA) system proved to be able to analyse up to 40 samples h^?1. Effects of various interferences possibly present in the water samples were investigated. Most cations and anions, as well as organic compounds, did not interfere with the determination of Cr(VI) in water samples. The experimental results obtained for chromium in reference materials were also in good agreement with the certified values.     

健那绿B的荧光猝灭研究及作为核酸测定探针的应用

用紫外可见光谱、稳态荧光发射及荧光寿命测定研究了核酸猝灭十二烷基磺酸钠胶束中的健那绿荧光。水溶液中弱的健那绿荧光在十二烷基磺酸钠胶束中被大大加强，其最大发射从425纳米移至410纳米，核酸的加入将猝灭健那绿的荧光，当健那绿浓度为2.5×10^–5 mol•L^-1时，荧光猝灭(F₀/F)分别与小牛胸腺DNA及鱼精DNA在2.4×10^–8 到 1.08×10^–7及 1.9×10^–8 到 3.8×10^–8 mol•L^-1范围内成正比, 检测限分别为1.3×10^–8 mol•L^-1 (小牛胸腺DNA)及6.3×10^–9 mol•L^-1 (鱼精DNA)。当DNA浓度较高时, 将系统偏离Stern-Volmer方程。这是因为动态猝灭和静态猝灭同时存在。方法已应用于鸡血提取液中DNA的测定, 测定结果与紫外法一致。     

Voltametric and Flow Injection Determination of Oxytetracycline Residues in Food Samples Using Carbon Fiber Microelectrodes

A voltammetric method for the determination of the antibiotic oxytetracycline (OTC) in food samples is reported. Carbon fiber microelectrodes (CFMEs), which allow voltammetric measurements to be performed in a small volume (1 mL) of the analyte extract from the samples, are employed. Repeatable electroanalytical responses were obtained with no need of applying cleaning treatments to the CFME. Under the optimized square‐wave conditions, a linear calibration plot for OTC was obtained in the 1.0×10^?6–1.0×10^?4 mol L^?1 range, with a detection limit of 2.9×10^?7 mol L^?1 (150 ng mL^?1) OTC. The determination of OTC by a flow‐injection method with amperometric detection using a homemade flow cell specially designed to work with CFMEs, was also evaluated using pure acetonitrile as the carrier. The SW voltammetric method was applied to the determination of OTC in spiked milk and eggs samples, at 100 ng mL^?1 and 200 ng g^?1 levels, respectively. The procedure involved the extraction of the analyte in ethyl acetate, evaporation of the solvent and reconstitution of the residue in acetonitrile ?5.0×10^?4 mol L^?1 tetrabutylammonium perchlorate medium. Recoveries of 96±8 and 91±8% were obtained for milk and eggs, respectively, by applying the standard additions method.     

Determination of Folic Acid by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of folic acid at an in situ plated lead film electrode was described. Formation of lead film on a glassy carbon substrate and accumulation of folic acid was performed simultaneously from an acetate buffer solution of pH 5.6 at the potential ?0.88 V. The measurements were carried out from aerated solutions. The calibration graph for an accumulation time of 300 s was linear from 2×10^?9 to 5×10^?8 mol L^?1. The detection limit was 7×10^?10 mol L^?1, the relative standard deviation for 2×10^?8 mol L^?1 of folic acid was 3.9%. The proposed procedure was applied to folic acid determinations in pharmaceutical preparations.     

Green Spectrophotometric Method for the Quantitative Analysis of Vancomycin in Pharmaceuticals and Comparison with HPLC

Abstract

A spectrophotometric method for the determination of vancomycin base, (VCM), and vancomycin hydrochloride, (HVCM), based on the reaction with copper (II) ions, is presented. The obtained detection limit is about 4.5×10^?5 mol L^?1. The working analytical range falls between 1.0×10^?3 mol L^?1 and 1.0×10^?2 mol L^?1. Recovery studies in presence of excipients were performed. The recovery results were compared with HPLC. For HVCM the proposed method presented similar recovery to that of HPLC, 100.4% vs. 100.2%, but better precision, 1.9% vs. 6.1%. In the VCM case the recovery is quite better, 100.5% vs. 89.6%, with a little smaller precision, 2.1% vs. 1.3%.     

On-line simultaneous pre-concentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry

An on-line pre-concentration system for the sequential determination of cadmium and lead in drinking water by using fast sequential flame atomic absorption spectrometry (FS-FAAS) is proposed in this paper. Two minicolums of polyurethane foam loaded with 2-(6-methyl-2-benzothiazolylazo)-orcinol (Me-BTAO) were used as sorptive pre-concentration media for cadmium and lead. The analytical procedure involves the quantitative uptake of both analyte species by on-column chelation with Me-BTAO during sample loading followed by sequential elution of the analytes with 1.0?mol?L^?1 hydrochloric acid and determination by FS-FAAS. The optimisation of the entire analytical procedure was performed using a Box–Behnken multivariate design utilising the sampling flow rate, sample pH and buffer concentration as experimental variables.

The proposed flow-based method featured detection limits (3σ) of 0.08 and 0.51?µg?L^?1 for cadmium and lead, respectively, precision expressed as relative standard deviation (RSD) of 1.63% and 3.87% (n?=?7) for cadmium at the 2.0?µg?L^?1 and 10.0?µg?L^?1 levels, respectively, and RSD of 6.34% and 3.26% (n?=?7) for lead at the 5.0?µg?L^?1 and 30.0?µg?L^?1 levels, respectively. The enrichment factors achieved were 38.6 and 30.0 for cadmium and lead, respectively, using a sample volume of 10.0?mL. The sampling frequency was 45 samples per hour. The accuracy was confirmed by analysis of a certified reference material, namely, SRM 1643d (Trace elements in natural water). The optimised method was applied to the determination of cadmium and lead in drinking water samples collected in Santo Amaro da Purificação City, Bahia, Brazil.     

Sorption Catalytic Determination of Copper(II) and L-α-alanine on Mg-, Al-Layered Double Hydroxides

Mg-, Al and Mg-, Cu-, Al-layered double hydroxides well-known synthetic hydrotalcite-like sorbents, were used for the first time as carriers for indicators in the sorption catalytic determination of copper(II) and L-α-alanine. Mg-, Al and Mg-, Cu-, Al-layered double hydroxides were synthesized by coprecipitation and characterized using infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The adsorption of 0.50?mg?L^?1 copper(II) solution by Mg-, Al-layered double hydroxides followed a pseudo-second-order model with an equilibrium sorption capacity of 24.2?×?10^?3?mg?g^?1 (3.8?×?10^?4?mmol g^?1) and a reaction rate constant of 4.2?g mg^?1?min^?1. Mg-, Al-layered double hydroxide tablets were prepared and used for sorption concentration and subsequent sensitive and selective sorption catalytic determination of 5.5?×?10^?3 to 1.0?mg?L^?1 copper(II) at the sorbent phase. The method was used for the analysis of natural water. A method was developed for the determination of α-alanine in Mg-, Cu-, Al-layered double hydroxide tablets with a limit of detection of 4.0?×?10^?3 mol?L^?1. In addition, thin layers of Mg-, Cu-, Al-layered double hydroxide were used to separate α-alanine and determine α-amino acids by thin-layer chromatography.     

Sensitive adsorptive stripping voltammetric method for direct determination of trace concentration of lead in the presence of cupferron in natural water samples

This paper reports the use of an adsorptive voltammetric technique for Pb(II) determination using cupferron as a selective complexing agent. After accumulation of the complex onto a hanging mercury drop electrode, the electrode potential was scanned with differential pulse modulation and the reduction current of lead was observed at about??0.5?V. Under optimum conditions (5?×?10^?4?mol?L^?1 cupferron concentration, 0.1?mol?L^?1 acetate buffer (pH 5.5), adsorption at??50?mV for 30?s) the detection limit was 5.1?×?10^?10?mol?L^?1. The relative standard deviation of five measurements for low lead concentration was 3.1%. The accuracy of the method was tested by analysing certified reference material (SPS-WW1 Waste Water). Finally, the method was successfully applied to the determination of Pb(II) in river water samples without any pretreatments.     

Flow injection determination of hydrogen peroxide using diperiodatoargentate- and diperiodatonickelate-luminol chemiluminescence

A novel chemiluminescence (CL) method for the determination of hydrogen peroxide is described. Method is based on the transition metals in highest oxidation state complex, which include diperiodatoargentate (DPA) and diperiodatonickelate (DPN) and show excellent sensitisation on the luminol-H₂O₂ CL reaction with low luminol concentration in alkaline medium. In particular, the sensitiser which was previously reported (such as Co²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe³⁺, Cr³⁺, KIO₄, K₃Fe(CN)₆ etc.) to be unobserved CL due to poor sensitisation with such low concentration of luminol which makes the method hold high selectivity. Based on this observation, the detection limits were 6.5?×?10^?9?mol?L^?1 and 1.1?×?10^?8?mol?L^?1 hydrogen peroxide for the DPN- and DPA-luminol CL systems, respectively. The relative CL intensity was linear with the hydrogen peroxide concentration in the range of 2.0?×?10^?8–6.0?×?10^?6?mol?L^?1 and 4.0?×?10^?8–4.0?×?10^?6?mol?L^?1 for the DPN- and DPA-luminol CL systems, respectively. The proposed method had good reproducibility with a relative standard deviation of 3.4% (8.0?×?10^?7?mol?L^?1, n?=?7) and 1.0% (2.0?×?10^?6?mol?L^?1, n?=?7) for the DPN- and DPA-luminol CL systems, respectively. A satisfactory result has been gained for the determination of H₂O₂ in rainwater and artificial lake water by use of the proposed method.