Determination of cysteine in a pharmaceutical formulation by flow injection analysis with a chemiluminescence detector

A simple and convenient flow injection-chemiluminescence (FI-CL) method for the determination of cysteine is reported, based on a fast and strong CL in a basic luminol-cysteine-NaIO₄ solution. The linear range was 1.0×10⁻⁸ to 1.0×10⁻⁶ M with a detection limit (3s) of 5×10⁻⁹ M, which was 100 times more sensitive than previously reported CL methods. Singlet oxygen, hydroxyl radical and hydrogen peroxide were suggested to be produced in this reaction and were responsible for the CL of cysteine. This simple method has been successfully applied for the determination of cysteine in a pharmaceutical formulation.     

Determination of paracetamol in pharmaceutical formulations using a sequential injection system

A simple method for the rapid determination of paracetamol in pharmaceutical formulations is described. The method involves oxidation of paracetamol by potassium hexacyanoferrate(III) and a subsequent reaction with phenol in the presence of ammonia. The blue complex formed is measured at 630 nm. The system has a sample frequency of 27 samples per h with a detection limit of 0.2 mg l⁻¹. The calibration curve is linear up to 60 mg l⁻¹ with a relative standard deviation of 1.2% (n=10).     

Determination of lithium in pharmaceutical formulations used in the treatment of bipolar disorder by flow injection analysis with spectrophotometric detection

In this work, a flow injection system with spectrophotometric detection was developed for the determination of lithium in pharmaceutical formulations used in the treatment of bipolar disorder. Reaction between Quinizarine (1,4-dihydroxyanthraquinone) and Li(I) ion in alkaline medium containing dimethylsulfoxide (DMSO) was explored for this purpose. The flow system was optimized regarding to its chemical (DMSO, Quinizarine and NaOH concentrations and sample pH) and physical parameters (sample loop volume, carrier flow rate and reactor length) in order to establish better conditions in terms of sensitivity and sampling frequency. The results obtained showed that the concentration of DMSO in the reagent solution presents remarkable influence on the magnitude of analytical signal. Chemical species that could be found in the formulations such as Na(I), K(I), Mg(II), Ca(II), Ti(IV), Cl⁻, CO₃²⁻ e sodium dodecylsulfate were tested as possible interfering ions. Among them, only non-monovalent cations presented noticeable interference on lithium signal. However, they were not found in concentrations high enough to cause interference in the determination of lithium in the samples. Sample preparation was performed by sonicating a slurry prepared by dispersing 100 mg of powdered sample in 15 mL of 0.10 mol L⁻¹ HCl solution. Results obtained by developed methodology were not statistically different from those obtained by flame emission spectrometry. In the optimized conditions the method presented a linear range of 5-40 mg L⁻¹ and a relative standard deviation of 3.6% at 5 mg L⁻¹ Li concentration. Detection and quantification limits were 0.54 and 1.8 mg L⁻¹, respectively. Sampling frequency, calculated as the time interval passed between two consecutive injections, was 60 samples per hour. The methodology was successfully applied in the determination of lithium in three commercial samples.     

Determination of flurbiprofen in pharmaceutical formulations by UV spectrophotometry and liquid chromatography

In this study, a new and rapid UV spectrophotometric (UV) method and a reversed phase high performance liquid chromatographic (LC) method were developed for quantitative estimation of flurbiprofen, a non-selective, non-steroidal, anti-inflammatory drug (NSAID), in pure form and in pharmaceutical dosage form. The solvent system, wavelength of detection, chromatographic conditions were optimized in order to maximize the sensitivity of both the proposed methods. The linear regression equations obtained by least square regression method were Abs=7.5906×10⁻² concentration (μg/ml) + (−) 4.6210×10⁻² for the UV method, and peak area=1.2652×10² concentration (ng/ml) + 1.4830×10³ for the LC method. The detection limit as per the error propagation theory was found to be 0.34 μg/ml for UV method and 15 ng/ml for LC method. The developed methods were successfully employed with high degree of precision and accuracy for the estimation of total drug content in two commercial ophthalmic drops of flurbiprofen. The results of analysis were treated statistically, as per USP 2000 and International Conference on Harmonization (ICH) guidelines for validation of analytical procedures, and by recovery studies. The results obtained from UV method were comparable with those obtained by using LC. It was concluded that both the developed methods are equally accurate, sensitive, precise, reproducible, robust and rugged and could be applied directly and easily to the pharmaceutical preparations of flurbiprofen. However, LC method is useful at very low level (ng/ml), whereas UV method is suitable at μg/ml level.     

Sensitive Determination of Nanogram Levels of Diacerein in a Pharmaceutical Formulation by Flow Injection Chemiluminescence Analysis

A simple, sensitive and inexpensive flow injection chemiluminescence (FI‐CL) method for the determination of diacerein was proposed. It was based on the greatly enhancive effect of diacerein on the CL reaction between luminol and hydrogen peroxide in alkaline medium. The enhanced CL intensity was linear with the concentration of diacerein over the range 1.0–500 ng/mL with a detection limit (3σ) of 0.2 ng/mL. The relative standard deviation was 1.1% (n = 8, 20 ng/mL diacerein) and the sample throughput was about 120 samples h^?1. This simple method has been successfully applied for the determination of diacerein in a pharmaceutical formulation without interference from its potential impurities. The degradation of diacerein was also investigated briefly.     

Flow injection analysis of doxycycline or chlortetracycline in pharmaceutical formulations with pulsed amperometric detection

A flow injection with pulsed amperometric detection for determination of doxycycline or chlortetracycline in pharmaceutical formulations is described. Doxycycline or chlortetracycline were studied at a gold rotating disk electrode with cyclic voltammetry as a function of pH of supporting electrolyte solution. The optimized PAD waveform parameters were obtained with a flow injection system. The optimized pulsed conditions of doxycycline were 1150 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 220 ms (150 ms delay time and 70 ms integration time), 1500 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized pulsed conditions of chlortetracycline were 1050 mV (versus Ag/AgCl reference electrode) detection potential (E_det) for 300 ms (200 ms delay time and 100 ms integration time), 1300 mV (versus Ag/AgCl reference electrode) oxidation potential (E_oxd) for 70 ms oxidation time (t_oxd) and 250 mV (versus Ag/AgCl reference electrode) reduction potentail (E_red) for 400 ms reactivation time (t_red). The optimized PAD waveform was applied to the determination of doxycycline hydrochloride and chlortetracycline hydrochloride standard solution and in pharmaceutical formulations. The linear dynamic ranges of doxycycline hydrochloride and chlortetracycline hydrochloride were 1 μM–0.1 mM. The sensitivity of this method was found to be 23 μA/mM for doxycycline hydrochloride and 33.76 μA/mM for chlortetracycline hydrochloride. The detection limit for both compounds is 1 μM. The doxycycline hydrochloride and chlortetracycline hydrochloride content in commercially available tablet dosage forms by the proposed method was comparable to those specified by the manufacturer.     

Flow-injection turbidimetric determination of homatropine methylbromide in pharmaceutical formulations using silicotungstic acid as precipitant reagent

A flow-injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with silicotungstic acid in acidic medium to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.1 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹, with a detection limit of 5.0 × 10⁻⁶ mol l⁻¹. The recoveries ranged from 96 to 103%, the sampling frequency was 70 determinations per hour and relative standard deviations were less than 1.5% (n = 10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method.     

流动注射化学发光法快速测定尿液中左亚叶酸钙

在碱性介质中, 左亚叶酸钙对鲁米诺-K3Fe(CN)6体系有显著的增敏作用, 据此, 建立了一种简单、快速测定左亚叶酸钙的流动注射化学发光新方法. 在优化的实验条件下, 该法测定左亚叶酸钙的线性范围为5.0×10-8～1.0×10-5 g/mL; 检出限(3σ)为2.0×10-8 g/mL; 对浓度为1.0×10-6 g/mL的样品进行11次平行测定, 相对标准偏差为1.3%. 将此法用于尿液中左亚叶酸钙的测定, 同时进行回收率实验.     

Flow-injection enhanced chemiluminescence method for determination of ciprofloxacin in pharmaceutical preparations and biological fluids

A novel rapid and sensitive analytical method, enhanced chemiluminescence with flow-injection sampling, is described for determination of ciprofloxacin. The method is based on the chemiluminescence reaction of the potassium permanganate–sodium thiosulfate–ciprofloxacin system. An enhanced chemiluminescence reaction was developed, and optimum conditions for CL emission were investigated. The chemiluminescence intensity was linearly dependent on ciprofloxacin concentration in the range 1.0×10⁻⁸–1.0×10⁻⁵ g mL⁻¹. The detection limit was 4×10⁻⁹ g mL⁻¹. The relative standard deviation was 1.8% for eleven measurements of 2.0×10⁻⁷ g mL⁻¹ ciprofloxacin standard solution. The new method enables simple, sensitive, and rapid determination of ciprofloxacin and has been successfully used for determination of ciprofloxacin in biological fluids and in ciprofloxacin hydrochloride tablet and injection.     

流动注射化学发光法测定褪黑素

在强碱性介质中,铁氰化钾可直接氧化褪黑素产生化学发光。基于此,建立了一种测定褪黑素的流动注射化学发光分析方法。线性范围为1.9×10-6~2.3×10-4g/mL,检出限为5×10-7g/mL,该法已用于药物中褪黑素的测定。     

Determination of antihelminthic drug pyrantel pamoate in bulk and pharmaceutical formulations using electro-analytical methods

Electrochemical behaviour of pyrantel pamoate has been studied by using different voltammetric and polarographic techniques in Britton Robinson buffer system. Differential pulse polarographic and cyclic voltammetric methods have been developed for the determination of drug in pharmaceutical formulation. A well-defined cathodic wave and one anodic peak were observed for the pyrantel pamoate in the entire pH range. Number of electrons transferred in the reduction process was calculated and the reduction mechanism postulated. The results indicate that the electrode process is reversible and diffusion controlled. The proposed method has been validated. The peak current is found to be linear over the concentration range 4 × 10⁻⁴ to 2 × 10⁻² mol L⁻¹. The lower detection limit (LOD) and lower limit of quantitation (LOQ) is found to be 2.45 × 10⁻⁵ and 8 × 10⁻⁵ mol L⁻¹.     

Electrochemical study and flow injection analysis of paracetamol in pharmaceutical formulations based on screen-printed electrodes and carbon nanotubes

Acetaminophenol or paracetamol is one of the most commonly used analgesics in pharmaceutical formulations. Acetaminophen is electroactive and voltammetric mechanistic studies for the electrode processes of the acetaminophenol/N-acetyl-p-quinoneimine redox system are presented. Carbon nanotubes modified screen-printed electrodes with enhanced electron transfer properties are used for the study of the electrochemical-chemical oxidation mechanism of paracetamol at pH 2.0.Quantitative analysis of paracetamol by using its oxidation process (in a Britton-Robinson buffer solution pH 10.0) at +0.20 V (vs. an Ag pseudoreference electrode) on an untreated screen-printed carbon electrode (SPCE) was carried out. Thus, a cyclic voltammetric based reproducible determination of acetaminophen (R.S.D., 2.2%) in the range 2.5 × 10⁻⁶ M to 1 × 10⁻³ M, was obtained. However, when SPCEs are used as amperometric detectors coupled to a flow injection analysis (FIA) system, the detection limit achieved for paracetamol was 1 × 10⁻⁷ M, one order of magnitude lower than that obtained by voltammetric analysis. The repeatability of the amperometric detection with the same SPCE is 2% for 15 successive injections of 10⁻⁵ M acetaminophen and do not present any memory effect.Finally, the applicability of using screen-printed carbon electrodes for the electrochemical detection of paracetamol (i.e. for quality control analysis) was demonstrated by using two commercial pharmaceutical products.     

Determination of noradrenaline and dopamine in pharmaceutical injection samples by inhibition flow injection electrochemiluminescence of ruthenium complexes

Two maximal potential-resolved flow injection-electrochemiluminescent (FI-ECL) peaks were observed for Ru(bpy)₃²⁺/TPrA system at 0.90 and 1.05 V, and for Ru(phen)₃²⁺/TPrA at 1.01 and 1.25 V (vs. Ag/AgCl) in pH 8.0 phosphate buffer solutions. Sensitive ECL inhibition effects were observed in the presence of noradrenaline and dopamine for both of these systems. Therefore, an FI-ECL inhibition method for determination of noradrenaline and dopamine has been developed. Under optimal conditions, linear responses between logarithm of ECL intensity changes and logarithm of sample concentration were found for noradrenaline in the linear range (LR) of 4×10⁻⁸-1×10⁻⁵ mol l⁻¹ with theoretical detection limit (DL) of 2.5×10⁻⁸ mol l⁻¹ for Ru(bpy)₃²⁺/TPrA system, and in LR of 2×10⁻⁸-2×10⁻⁵ mol l⁻¹ with DL of 7.1×10⁻⁹ mol l⁻¹ for Ru(phen)₃²⁺/TPrA system; and for dopamine in LR of 8×10⁻⁸-2×10⁻⁵ mol l⁻¹ with DL of 5.2×10⁻⁸ mol l⁻¹ for Ru(bpy)₃²⁺/TPrA system, in LR of 4×10⁻⁸-2×10⁻⁵ mol l⁻¹ with DL of 1.5×10⁻⁸ mol l⁻¹ for Ru(phen)₃²⁺/TPrA system. It was applied for determination of commercial pharmaceutical injection samples with satisfied results. The mechanism of the inhibition effects was proposed in the preliminary way.     

Determination of iodide by detection of iodine using gas-diffusion flow injection and chemiluminescence

This work describes development of a flow injection (FI) system for determination of iodide, based on the chemiluminescence (CL) reaction between iodine and luminol. Iodide in the sample zone is oxidized to iodine. Employment of a gas-diffusion (GD) unit allows for selective detection of the generated CL (425 nm). Preliminary results showed for concentrations of less than 2 mg L⁻¹, that signals were irreproducible and that the calibration was not linear.In order to solve these problems, a method of ‘membrane conditioning’ was investigated, in which iodide stream was continuously merged with oxidant to generate I₂ that conditioned the GD membrane and tubing. This minimized surface interaction between the active surface and the I₂ generated from the samples, thus improving both precision and sensitivity. By employing membrane conditioning, it has been possible to reliably detect concentrations down to 0.1 mg L⁻¹.At the optimized condition, an excellent linear calibration (r² = 0.999) was obtained from 0.1 to 1.0 mg L⁻¹. The method was successfully applied to determine iodide in some pharmaceutical products such as potassium iodide tablets and a liquid patent medicine. However, for vitamin tablets, ascorbic acid was found to interfere seriously by causing a negative signal.     

Chiral separation of Huperzine A using CE - method validation and application in pharmaceutical formulations

The aim of this work is the development, validation and application of an MEKC method for the chiral separation of Huperzine A. Huperzine A is an important compound that is used to treat Alzheimer's disease. However, only the (?)‐form of this compound is biologically active and behaves as a potential acetylcholinesterase inhibitor. Therefore, the separation of the (?)‐form from the (+)‐form is of greatest importance. Optimal conditions, regarding resolution and analysis time, were established by altering several experimental parameters, such as temperature, field strength, pH, type and concentration of BGE and chiral selector. A major problem that had to be solved in this study was the low intensity and efficiency of the peaks. More parameters were examined, such as the addition of modifiers, to optimize further the separation, and particularly the efficiency. Baseline enantioseparation was achieved by using a BGE of 50 mM acetate (pH 5.0), supplemented with 0.2% w/v poly(sodium N‐undecanoyl‐ll ‐alanyl‐valinate) and 10% v/v tert‐butanol. Finally, the optimum conditions were applied to a pharmaceutical formulation, to demonstrate the ability of the method to control the purity of the (?)‐Huperzine A in pharmaceutical formulations.     

流动注射化学发光法测定DL-酪氨酸

在甲醛存在下 ,高锰酸钾与DL 酪氨酸能够发生化学发光反应 ,产生很强的化学发光。据此采用流动注射技术 ,建立了一种测定DL 酪氨酸的化学发光分析法。方法的检出限为 2 .9× 1 0 - 8g/mL ,相对标准偏差为 1 .5 % ( 1 .0× 1 0 - 6g/mLDL 酪氨酸 ,n =1 1 ) ,线性范围为 1 .0× 1 0 - 7g/mL～ 5 .0× 1 0 - 6g/mL。     

药物中抗坏血酸的顺序注射光度法的研究

基于抗坏血酸在H2SO4介质中能把Fe3 还原成Fe2 ,并与2,2′ 联吡啶生成有色络合物的原理,建立了顺序注射分光光度测定药物中抗坏血酸的方法。实验参数采用单因素法进行优化,优化后Fe3 的浓度为0 005mol L,2,2′ 联吡啶的质量浓度为2 5g L,流速为6mL min。在300μL进样体积下方法的检出限为0.18μg mL(3σ),RSD为1.6%(n=11),采样频率为60样 h。一般的赋形剂不产生干扰,测定结果与标准方法无显著性差异,适合于制药过程中的质量在线监测。     

流动注射化学发光法测定甲硝唑

在碱性条件下 ,铁氰化钾氧化鲁米诺产生化学发光 ,甲硝唑对该体系有显著的增强作用 (亚铁氰化钾存在时 )。基于此 ,建立了流动注射化学发光测定痕量甲硝唑的新方法。甲硝唑浓度在 2 .0× 1 0 -6～ 4 .0× 1 0 -4 mol L范围内与发光强度呈良好的线性关系 ;检出限 (3σ)为 1 .5× 1 0 -7mol L。相对标准偏差 (c =1 .0× 1 0 -5mol L ,n=1 1 )为 3.6 %。方法已用于制剂中甲硝唑含量测定     

Potassium permanganate-glyoxal chemiluminescence system for flow injection analysis of cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium in pharmaceutical preparations

A sensitive flow injection chemiluminescence (FL-CL) method for the determination of cephalosporin antibiotics, was developed. The method was based on that cephalosporin antibiotics could enhance the CL reaction of glyoxal and KMnO₄ in sulfuric acid. Method development included the optimization of reagent concentrations and flow-rate. Under the optimized conditions, three cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium, were determined. The detection limits of the method are 10 ng ml⁻¹ cefalexin, 2 ng ml⁻¹ cefadroxil, and 2 ng ml⁻¹ cefazolin sodium. The method was successfully applied to the determination of three cephalosporin antibiotics in pharmaceutical preparations.     

Determination of gentamicin in pharmaceutical formulations using peroxyoxalate chemiluminescent detection in flow-injection analysis

A simple and sensitive procedure for the determination of gentamicin is presented, based on the use of the peroxyoxalate chemiluminescent (PO-CL) system in presence of imidazole as a catalyst. The gentamicin has to be previously derivatized with o-phthaladehyde (OPA) in order to obtain a fluorophore, which participates in the PO reaction, producing a CL emission proportional to the gentamicin concentration. The method is developed by using a particular flow-injection analysis (FIA) manifold, employing sodium dodecyl sulfate (SDS) micellar medium as a carrier in order to avoid the degradation of PO in water. The optimization of the instrumental and chemical variables affecting the CL reaction was rigorously carried out by using experimental design methodology. The method has been successfully applied to pharmaceutical formulations.