Flow‐Based Fluorimetric Determination of Furosemide in Pharmaceutical Formulations and Biological Samples: Use of Micelar Media to Improve Sensitivity

Abstract

Two fast flow injection procedures with fluorimetric detection based on the furosemide emission are presented. The first configuration used a phosphate buffer solution pH 3.00, 0.2 ionic strength (μ) solution flowing at 3.0 ml min^?1 as carrier, a 80 cm sample loop (400 µl total sample injection), and a 40 cm long reactor coil, which was kept at room temperature; the second has a unique difference: the introduction of a new channel of surfactant solution with reduction of flow rate. The excitation and emission were carried out at 270 and 410 nm, respectively; both systems presented linear dynamic range from 1.0×10^?7 to 1.0×10^?5 mol l^?1. The limit of detection (3σ/slope) was 3.0×10^?8 mol l^?1, to the first system, and 10^?8 mol l^?1 for the second one. Both proposed methods were applied to three commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte. They presented an analytical frequency of 90 and 60 measurements per hour, respectively to phosphate and micelar media. The results agreed with those from the label and determined by a UV‐Vis spectrophotometric comparative procedure. Recoveries around 101% were found in the commercial formulations and synthetic urine matrixes.     

Pattern Recognition of Sweeteners in Biological Fluids,Beverages, and Ketchup using Stochastic Sensors

Three stochastic sensors based on nanodiamond (nDP) paste modified with α, β, and γ‐cyclodextrin were designed and characterized for pattern recognition of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and biological fluids. The linear concentration ranges obtained for acesulfame K (between 1.00×10^?10 mol L^?1and 1.00×10^?3 mol L^?1), for aspartame (between 1.00×10^?12 mol L^?1 and 1.00×10^?3 mol L^?1) and for sodium cyclamate (between 4.97×10^?12 mol L^?1 and 4.97×10^?3 mol L^?1) allow their assay in biological fluids, beverages and ketchup. The lowest limits of quantification were obtained using the stochastic sensor based on γ‐CD/nDP: for acesulfame K 1.00×10^?10 mol L^?1, for aspartame 1.00×10^?12 mol L^?1 and for sodium cyclamate 4.97×10^?12 mol L^?1. All three stochastic sensors revealed very high values of sensitivities. The proposed method was reliable for qualitative and quantitative assay of aspartame, acesulfame K and sodium cyclamate in beverages, ketchup, and in biological fluids such as urine.     

Highly Selective Potentiometric Sensor for Determining Phenazopyridine Hydrochloride in Biological Fluids Using N,N′-(Pyromellitoyl)-bis-L-tyrosine Dimethyl Ester

A new membrane selective electrode based on the potentiometric method was developed for the determination of phenazopyridine. The membrane signal is based on the interaction of N,N′-(pyromellitoyl)-bis-L-tyrosine dimethyl ester with phenazopyridine. The sensor displays a linear response with a slope of 61.1 mV decade^?1 for phenazopyridine concentrations in the range of 1.0 × 10^?2–1.0 × 10^?5 mol L^?1 and with detection limit of 8.0 × 10^?6 mol L^?1 of phenazopyridine. The electrode enjoys a fast response time. Application of this potentiometric sensor for phenazopyridine determination in pharmaceuticals, urine, and blood serum samples is reported without any special pretreatment required.     

Determination of Minoxidil by Bleaching the Permanganate Carrier Solution in a Flow-Based Spectrophotometric System

The determination of minoxidil (MX) with potassium permanganate as a carrier in a flow injection method is described. The detection at 550 nm was linear from 1.0 × 10^?5 to 5.0 × 10^?4 mol L^?1. The limit of detection (3σ/slope) was 8.92 × 10^?6 mol L^?1, with an analytical frequency of 32 h^?1. The proposed method was applied to commercial samples, with recoveries from 104.7 to 106.4%. Comparison with the HPLC procedure reveled relative errors from 0.48 to 1.4%, and the results agreed within a 95% confidence level.     

Direct Electroanalytical Determination of Fluvastatin in a Pharmaceutical Dosage Form: Batch and Flow Analysis

Abstract

The reduction of luvastatin (FLV) at a hanging mercury-drop electrode (HMDE) was studied by square-wave adsorptive-stripping voltammetry (SWAdSV). FLV can be accumulated and reduced at the electrode, with a maximum peak current intensity at a potential of approximately ?1.26 V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity between peak current intensity and FLV concentration between 1.0 × 10^?8 and 2.7 × 10^?6 mol L^?1. Limits of detection (LOD) and quantification (LOQ) were found to be 9.9 × 10^?9 mol L^?1 and 3.3 × 10^?8 mol L^?1, respectively.

Furthermore, FLV oxidation at a glassy carbon electrode surface was used for its hydrodynamic monitoring by amperometric detection in a flow-injection system. The amperometric signal was linear with FLV concentration over the range 1.0 × 10^?6 to 1.0 × 10^?5 mol L^?1, with an LOD of 2.4 × 10^?7 mol L^?1 and an LOQ of 8.0 × 10^?7 mol L^?1. A sample rate of 50 injections per hour was achieved.

Both methods were validated and showed to be precise and accurate, being satisfactorily applied to the determination of FLV in a commercial pharmaceutical.     

Enzymes Immobilized on a Tubular Reactor for Fast Amperometric Determination of Glucose in Brazilian Honey

Abstract

Glucose present in honey was rapidly determined by the differential amperometric method using two tubular reactors containing glucose oxidase and peroxidase. The linear dynamic range extends from 5 × 10^?5 to 2 × 10^?4mol L^?1, at pH 7.0. At flow rate of 1.5 mL min^?1 and injecting 150-µL sample volumes, a sampling frequency of the 33 determinations per hour is afforded. The reproducibility of the methods showed a relative standard deviation (RSD) < 4%. The detection limit of this method is 1.7 × 10^?5 mol L^?1. The samples analyses were compared with the parallel spectrophotometric determination.     

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.     

The New Application of Boron Doped Diamond Electrode Modified with Nafion and Lead Films for Simultaneous Voltammetric Determination of Dopamine and Paracetamol

A new voltammetric procedure for the simultaneous determination of dopamine (DA) and paracetamol (PA) using boron doped diamond electrode modified with Nafion and lead films (PbF/Nafion/BDDE) was investigated. The use of this electrode resolved the overlapped voltammetric waves of DA and PA into well‐defined peaks with peak to peak separation of about 320 mV. Under the optimized experimental conditions in differential pulse voltammetric technique, DA and PA gave a linear response over the ranges 2.0×10^?7–1.0×10^?4 mol L^?1*(R²=0.9996) and 5.0×10^?7–1.0×10^?3 mol L^?1 (R²=0.9979), respectively. The detection limits were found to be 5.4×10^?8 mol L^?1 for DA and 1.4×10^?7 mol L^?1 for PA. They are lower, comparable or in some cases a little bit higher than those obtained using other electrochemical sensors. However, the proposed procedure of the sensor preparation is much simpler than procedures described in the literature with a lower detection limit. The proposed procedure was successfully applied to the determination of PA in some commercial pharmaceuticals as well as to the simultaneous determination of DA and PA in human urine, whole blood and serum samples directly without any separation steps.     

Molecular Imprinting-Chemiluminescence Sensor for the Determination of Prulifloxacin

Abstract

A selective molecular imprinting-chemiluminescence sensor is developed for the determination of prulifloxacin by using a prulifloxacin-imprinted polymer as recognition material and the cerium(IV)/sodium thiosulfate/prulifloxacin chemiluminescence reaction as the detection system. The linear response range of the sensor is from 8.0 × 10^?8 to 7.0 × 10^?6 mol L^?1 with a detection limit of 2.0 × 10^?8 mol L^?1. The relative standard deviation for 5.0 × 10^?7 mol L^?1prulifloxacin solution is 1.3% (n = 7). This sensor has been applied to the determination of prulifloxacin in urine samples, and the results obtained are satisfactory.     

Flow-Injection Chemiluminescent Determination of Piroxicam Using Tris (2,2′-bipyridyl) Ruthenium(II)—Potassium Permanganate System

Abstract

A rapid and sensitive chemiluminescence method using flow-injection has been developed for the determination of an analgesic agent drug, piroxicam. The method is based on the chemiluminescence reaction of piroxicam with an acidic potassium permanganate and Ru(bipy)₃ ²⁺. The chemiluminescence intensity is greatly enhanced when quinine sulfate is used as a sensitizer. After optimization of the different experimental parameters, a calibration graph was obtained over a concentration range of 3.0 × 0^?8–3.0 × 0^?5 mol L^?1 with the detection limit of 1.0 × 0^?8 mol L^?1. The relative standard deviation is 1.5% (n = 11) for the determination of 8.0 × 10^?7 mol L^?1 piroxicam. The proposed method was successfully applied to commercial tablets, spiked serum, and urine samples.     

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.     

Differential Pulse Voltammetric Determination of Sildenafil Citrate (Viagra®) in Pharmaceutical Formulations Using a Boron-Doped Diamond Electrode

The determination of sildenafil citrate using differential pulse voltammetry and a cathodically pre-treated boron-doped diamond electrode is described. The obtained analytical curve is linear in the sildenafil concentration range 7.3 × 10^?7 ? 7.3 × 10^?6 mol L^?1 in a 0.1 mol L^?1 H₂SO₄, with a detection limit of 6.4 × 10^?7 mol L^?1. The proposed method, which is fast and simple to carry out, was successfully applied in the determination of sildenafil citrate in Viagra® pharmaceutical formulations, with results in close agreement (at 95% confidence level) with those obtained using a comparative HPLC method.     

Studies on reaction of reduced lipoic acid with Mukaiyama reagent and its application for pharmaceutical and food analysis

A new sensitive method for the determination of lipoic acid (LA) in selected food items based on its reaction with Mukaiyama reagent (2-chloro-1-methylpyridinium iodide, CMPI) was developed. It was stated that CMPI reacts with reduced form of lipoic acid (dihydrolipoic acid, DHLA) and the stable product is produced. The spectrum of the labeled form of DHLA exhibits new band at 312?nm. Based on its spectral characteristics new spectrophotometric and UV–high-performance liquid chromatography (HPLC) methods of LA determination were elaborated. Both methods allowed determination of the analyte in the concentration range of 5?×?10^?6–1?×?10^?4?mol?L^?1 with limit of detection 0.39?×?10^?6 and 0.77?×?10^?6?mol?L^?1 for spectrophotometric and HPLC method, respectively. The practical usability of newly developed methods was checked by determination of lipoic acid contents in its pharmaceutical preparate Revitanerw. The proposed method was precise and accurate. The relative error of determination did not exceed ±0.067%. As chromatographic method allowed the determination of analyte in the presence of complex matrix, it was applied for assay of free fraction of α-lipoic acid in selected food items. A procedure of LA isolation from biological matrix was developed. The extraction with dichloromethane allowed quantitative recovery at 102.94?±?4.20%. The green barley appeared to be the richest source of LA.     

Determination of Trace of Cobalt in Complex Matrices by Adsorptive Stripping Voltammetry at a Lead Film Electrode

An adsorptive stripping voltammetric procedure for the determination of cobalt in a complex matrices at an in situ plated lead film electrode was described. The procedure exploits the enhancement effect of a cobalt peak observed in the system Co(II)–nioxime–piperazine‐1,4‐bis(2‐ethanesulfonic acid)–cetyltrimethylammonium bromide. The calibration graph was linear from 5×10^?10 to 2×10^?8 mol L^?1 and from 1×10^?10 to 1×10^?9 mol L^?1 for the accumulation times 120 and 600 s, respectively. The detection limit (based on the 3 σ criterion) for Co(II) following accumulation time of 600 s was 1.1×10^?11 mol L^?1. The interference of high concentrations of foreign ions and surfactants was studied.     

Sensitive Determination of Prulifloxacin by Its Fluorescence Enhancement on Terbium(III)–Sodium Dodecylbenzene Sulfonate System

Abstract

A terbium-sensitized fluorescence spectrophotometry method using an anionic surfactant, sodium dodecyl benzene sulphonate (SDBS), was developed for the determination of prulifloxacin (PUFX). It was found that SDBS significantly enhanced the fluorescence intensity of the PUFX–Tb³⁺ complex (about 13-fold). The optimal experimental conditions were determined as follows: excitation and emission wavelengths of 290 nm and 545 nm, pH 8.0, 4.0 × 10^?5 mol L^?1 terbium(III), and 4.0 × 10^?4 mol L^?1 SDBS. The enhanced fluorescence intensity of the system (ΔF) showed a good linear relationship with the concentration of PUFX over the range 6.0 × 10^?8 to 2.0 × 10^?6mol L^?1 with a correlation coefficient of 0.9991. The detection limit (S/N = 3) was determined as 8.5 × 10^?9 mol L^?1. This method has been successfully applied for the determination of PUFX in pharmaceuticals and human urine/serum samples. Compared with most other methods reported, the rapid and simple procedure proposed here offered higher sensitivity, wider linear range, and good stability. The luminescence mechanism of the system was also discussed in detail. In the fluorescence system of PUFX–Tb³⁺–SDBS, SDBS acted not only as the surfactant but also as the energy donor.     

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%.     

Anodic Stripping Voltammetric Determination of Aurothiomalate in Urine Using a Screen‐Printed Carbon Electrode

This work describes an electroanalytical method for determining gold(I) thiomalate, aurothiomalate, widely used for treatment of reumatoid arthiritis, using a screen‐printed carbon electrode (SPCE). Aurothiomalate (AuTM) was determined indirectly at the same electrode by accumulating it first at ?1.5 V vs. printed carbon. At this potential in the adsorbed state, the AuTM is reduced to Au(0), which is then oxidized at two steps at ?0.22 V and +0.54 V on SPCE. Using optimized conditions of 60 s deposition time, ?1.5 V (vs. printed carbon) accumulation potential, 100 mV s^?1 scan rate, linear calibration graphs can be obtained by monitoring the peak at +0.54 V for AuTM in HCl 0.1 mol L^?1 from 1.43×10^?6 to 1.55×10^?4 mol L^?1. A limit of detection obtained was 6.50×10^?7 mol L^?1, and the relative standard deviation from five measurements of 3.0×10^?5 mol L^?1 AuTM is 4.5%. The method was successfully applied for AuTM determination in human urine sample.     

Fluorescence Probe Enhanced Spectrofluorimetric Method for the Determination of Prulifloxacin in Pharmaceutical Formulations and Biological Fluids

Abstract

Spectrofluorimetry for the determination of prulifloxacin (PUFX) was developed based on the strong fluorescence of PUFX after adding fluorescence probe yttrium in buffer solution (pH = 6.80), and various factors of influencing fluorescence have been researched. Under the optimum conditions, the liner range was 2.0 × 10^?8 to 9.1 × 10^?6 mol L^?1 and the detection limit was 8.5 × 10^?9 mol L^?1. The relative standard deviation was 2.1% for 11 measurements of 5.0 × 10^?7 mol L^?1 PUFX standard solution. The mechanism of the sensitizing effect of probe was discussed. The method was applied for the determination of PUFX in actual sample; the result obtained was satisfactory.     

Flow Injection Spectrophotometric Determination of N-Acetylcysteine and Captopril Employing Prussian Blue Generation Reaction

A novel flow injection procedure to determine N-acetylcysteine and captopril in pharmaceutical formulations is proposed. The flow procedure developed was based on oxidation of the analytes by Fe(III) in acidic medium and subsequent reaction of the Fe(II) generated with excess hexacyanoferrate(III) to produce soluble Prussian blue (KFe[Fe(CN)₆]) measured at 700 nm. Detection limits of 1.0 × 10^?5 mol L^?1 and 3.0 × 10^?5 mol L^?1 for N-acetylcysteine and captopril, respectively, were found. The sample throughput was 70 h^?1 for both analytes and the results obtained were in agreement at a 95% confidence level with those obtained using reference methods.     

Voltammetric Determination of Folic Acid Using a Graphite Paste Electrode

A simple differential pulse voltammetric method based on a graphite paste electrode (GPE) was developed for the quantitative determination of folic acid (FA) in tablets. The electrode exhibits a clear improvement of the current response. A linear response in the electroanalytical approach exists from 4.97×10^?6 to 2.94×10^?5 mol L^?1 with a limit of detection of about 2.67×10^?6 mol L^?1 in KCl solutions. The developed procedure was tested by recovery studies and compared with spectrophotometric and chromatographic methods. The results are described and discussed in the light of existing literature.