Flow injection amperometric determination of L-dopa, epinephrine or dopamine in pharmaceutical preparations

Voltammetric analysis of epinephrine using glassy carbon electrode modified with nanocomposite prepared from Co-Nd bimetallic nanoparticles, alumina nanoparticles and functionalized multiwalled carbon nanotubes

Herein, we investigated the electrochemical behaviour of fMWCNTs decorated with Co-Nd bimetallic nanoparticles and alumina nanoparticles (Co-Nd/Al2O3@fMWCNTs). The nanocomposites were synthesised using simple mechanical mixing and characterised by FT-IR, XRD, UV-visible studies, SEM, TEM and EDAX. Moreover, the crystalline size of the synthesised nanoparticles was also calculated using XRD data (Debye-Scherer formula) and was found in the nm range. The electrochemical behaviour of epinephrine (EP) was examined in the presence of Co-Nd/Al2O3@fMWCNTs nanocomposite modified glassy carbon electrode (GCE) using various electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. Among all the above-mentioned techniques, the DPV response of the modified Co-Nd/Al2O3@fMWCNTs/GCE under optimal circumstances revealed a dual linear range (0.2 to 4000 µM and 4000 to 14,000 µM) and LOD of 0.015 µM (S/N = 3). The sensitivities were determined to be 0.00323 µAµM-1 and 0.0004 µAµM-1 in 0.2 to 4000 µM and 4000 to 14,000 µM concentration ranges. Using chronocoulometry, the surface coverage of Co-Nd/Al2O3@fMWCNTs/GCE was calculated to be 1.37 × 10-8 mol cm-2. The fabricated Co-Nd/Al2O3@fMWCNTs/GCE demonstrated remarkable repeatability, with an RSD of 0.09%, and storage stability of 3 weeks, with 89.6% current retention. Lastly, it was found that Co-Nd/Al2O3@fMWCNTs/GCE worked well for EP analysis in a variety of biological fluids.

Trypsin mediated one-pot reaction for the synthesis of red fluorescent gold nanoclusters: Sensing of multiple analytes (carbidopa, dopamine, Cu2+, Co2+ and Hg2+ ions)

Herein, we fabricated fluorescent gold nanoclusters (Au NCs) by using trypsin as a ligand. The fabricated trypsin-Au NCs emit bright red color fluorescence upon the exposure of 365 nm UV light. The trypsin-Au NCs are stable and well dispersed in water, which exhibited strong red emission peak at 665 nm upon excitation wavelength of 520 nm. The red fluorescence of trypsin-Au NCs was greatly quenched by the addition of multiple analytes such as drugs (carbidopa and dopamine) and three divalent metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion). As a result, a novel fluorescence "turn-off" probe was developed for the detection of the above analytes with good selectivity and sensitivity. This method exhibits the detection limits for carbidopa, dopamine, Cu²⁺, Co²⁺ and Hg²⁺ ions are 6.5, 0.14, 5.2, 0.0078, and 0.005 nM, respectively. The trypsin-Au NCs were successfully applied to detect drugs (carbidopa, and dopamine) in pharmaceutical samples and metal ions (Cu²⁺, Co²⁺ and Hg²⁺ ion) in biofluids and water samples, exhibiting good precision and accuracy, which offers a facile analytical strategy for assaying of the above analytes in pharmaceutical and biological samples.

Development and validation of a simple spectrophotometric method for the determination of methyldopa in both bulk and marketed dosage formulations

A simple, precise, sensitive, rapid, specific and economical spectrophotometric method was developed to determine methyldopa (MTD) content in bulk and pharmaceutical dosage formulations. The proposed method was based on the formation of a colored product from the nitrosation reaction of MTD with sodium nitrite in an acid medium. The resultant nitroso derivative species reacts further with sodium hydroxide and is converted it into a more stable compound. This yellow nitrosation product exhibited an absorption maximum at 430 nm. Beer's Law was obeyed in a concentration range of 6.37 to 82.81 μg mL-1 MTD with an excellent coefficient of determination (R2 = 0.9998). No interference was observed from common excipients in formulations. The results showed the method to be simple, accurate and readily applied for the determination of MTD in pure form and in pharmaceutical preparations. The analytical results obtained for these products using the proposed method are in agreement with those of the Brazilian Pharmacopoeia procedure at a 95% confidence level.

Highly sensitive trivalent copper chelate-luminol chemiluminescence system for capillary electrophoresis detection of epinephrine in the urine of smoker

Epinephrine (EP) is one of the most important neurotransmitters and hormones. Some previous literatures show that there is a close relation between its release and smoking. To compare the levels of EP in urines of smokers and nonsmokers, a sensitive chemiluminescence (CL) system, luminol-diperiodatocuprate (III) (K(5)[Cu(HIO(6))(2)], DPC), has been developed and validated for the determination of EP after CE separation. The DPC-luminol-EP CL reaction showed very intensive emission and fast kinetic characteristics, thus led to a high sensitivity in the flow-through detection mode for capillary electrophoresis. With the peak height as a quantitative parameter, the relative CL intensity was linear with the EP concentration in the range of 2.0-400ng/mL, with a limit of detection of 0.82ng/mL (S/N=3). The reproducibility was assessed by intra- and inter-day relative standard deviations (RSDs) for 11 replicate determinations of EP standard samples at low, medium and high concentrations. The intra- and inter-day RSDs for CL signals were 5.5%-6.6% and 6.1%-7.5%, respectively, and those for migration times were 3.4%-5.8% and 4.3%-6.3%, respectively. The presented method was successfully applied to the determination of EP in EP injection and urine samples of smokers and nonsmokers. The recovery test results for urine samples ranged from 86.5 to 112.0%, which demonstrated the reliability of this method. The results for urine sample detection indicate that the average level of EP in the urines of the smoker group is obviously higher than that in the urines of the nonsmoker group, which may demonstrate that smoking can stimulate the release of EP in human body.

Flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter. A review

Dopamine (DA) is one of the most important catecholamine neurotransmitters in the human central nervous system in the brain and plays a key role in the functioning of the renal, hormonal, and cardiovascular systems. Abnormal levels of dopamine are related to neurological disorders, such as schizophrenia and Parkinson's disease and the control and fluctuations of the amount of dopamine are extremely important in monitoring with analytical systems in the human brain. This review covers the attributes of flow-injection analysis systems with different detection devices and other related techniques for the in vitro and in vivo determination of dopamine as neurotransmitter and points out the advantages and disadvantages in the implementation thereof.

Simultaneous kinetic determination of levodopa and carbidopa by H-point standard addition method

The kinetic H-point standard addition method (HPSAM) was applied to the simultaneous determination of levodopa and carbidopa. The method was based on the difference in the rate of oxidation of these compounds with Cu(II)-neocuproine system and formation of Cu(I)-neocuproine complex at pH 5.5. The absorbance of the Cu(I)-neocuproine complex was monitored at 453 nm. Experimental conditions such as pH, reagent concentrations, ionic strength and temperature were optimized. Simultaneous determination of levodopa and carbidopa was performed in the range of 0.8-4 and 0.2-1.5 microg ml(-1), respectively. The proposed method was applied to the simultaneous determination of levodopa and carbidopa in pharmaceutical samples, and satisfactory results were obtained.

The nano-Au self-assembled glassy carbon electrode for selective determination of epinephrine in the presence of ascorbic acid

Gold nanoparticles were self-assembled to the modified glassy carbon electrode (GC) with cysteamine (CA) to prepare the nano-Au/CA/GC modified electrode. The electrochemical behavior of epinephrine (EP) on the modified electrode was explored with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Epinephrine gave a pair of redox peaks at E(pa)=0.190 mV and E(pc)=-0.224 mV (versus SCE), respectively. The nano-Au/CA/GC modified electrode shows an excellent electrocatalytic activity for the oxidation of EP. The modified electrode could be used to determine EP in the presence of ascorbic acid (AA). The response of catalytic current with EP concentration shows a linear relation in the range of 1.0 x 10(-7) to 5.0 x 10(-4) mol L(-1) with the correlation coefficient of 0.998. The detection limit is 4.0 x 10(-8) mol L(-1). The modified electrode exhibited a good reproducibility, sensitivity and stability for the determination of EP injection.

Epinephrine quantification in pharmaceutical formulations utilizing plant tissue biosensors

A plant tissue biosensor associated with flow injection analysis is proposed to determine epinephrine in pharmaceutical samples. The polyphenol oxidase enzymes present in the fibers of a palm tree fruits (Livistona chinensis), catalyses the oxidation of epinephrine to epinephrinequinone as a primary product. This product is then electrochemically reduced (at -0.10 V versus Ag/AgClsat) on the biosensor surface and the resulting current is used for the quantification of epinephrine. The biosensor provides a linear response for epinephrine in the concentration range from 5.0 x 10(-5) to 3.5 x 10(-4) mol l(-1). The limit of detection estimated for this interval was 1.5 x 10(-5) mol l(-1) and the correlation coefficient of 0.998, working under a flow rate of 2.0 ml min(-1) and using a sample loop of 100 microl. The repeatability (R.S.D. for 10 consecutive determinations of a 3.0 x 10(-4) mol l(-1) epinephrine solution) was 3.1%. The results obtained by the method here proposed were compared with the official UV spectrophotometric procedure and also using a plant tissue reactor. The responses obtained with the proposed strategies were in good agreement with both ways of analyses, whereas the values obtained by the official spectrophotometric method was strongly affected by benzoic acid, present in the formulation of pharmaceutical product utilized for inhalation. Such favorable results obtained with the carbon paste biosensor or utilizing the bioreactor, joined with the simplicity of its preparation turns these procedures very attractive for epinephrine quantification in pharmaceutical products.

Spectrophotometric determination of methyldopa in pharmaceutical formulations

A new, simple, precise, rapid and low-cost spectrophotometric method for methyldopa determination in pharmaceutical preparations is described. This method is based on the complexation reaction of methyldopa with molybdate. Absorbance of the resulting yellow coloured product is measured at 410 nm. Beer's Law is obeyed in a concentration range of 50 - 200 µg ml-1 methyldopa with an excellent correlation coefficient (r = 0.9999). No interference was observed from common excipients in formulations. The results show a simple, accurate, fast and readily applied method to the determination of methyldopa in pharmaceutical products. The analytical results obtained for these products by the proposed method are in agreement with those of the Brazilian Pharmacopoeia procedure at 95% confidence level.

A disposable electrochemical sensor for the rapid determination of levodopa

Levodopa (L-dopa), the biological precursor of catecholamines, is the most widely prescribed drug in the treatment of Parkinson's disease. The present work presents a proposal for the application of a gold screen-printed electrode an electrochemical sensor for monitoring L-dopa in stationary solution and a flow system. Using the electrooxidation of L-dopa at +0.63 V in acetate buffer pH 3.0 on a gold screen-printed electrode it is possible to obtain a linear calibration curve from 9.9 x 10(-5) to 1.2 x 10(-3) mol L(-1) and a detection limit of 6.8 x 10(-5) mol L(-1). Under amperometric conditions (E(app) = 0.8 V; flow rate = 14.1 mL min(-1); pH 3.0), an analytical calibration graph for l-dopa was obtained from 1.0 x 10(-6) mol L(-1) 6.6 x 10(-4) mol L(-1) with a detection limit of 9.9 x 10(-7) mol L(-1). The method was successfully applied to the determination of L-dopa in commercial dosage forms without any pre-treatment.

Flow-injection amperometric determination of dopamine in pharmaceuticals using a polyphenol oxidase biosensor obtained from soursop pulp

The amperometric determination of dopamine (Do) in pharmaceuticals formulations by flow injection analysis (FIA) is proposed. An enzymatically modified carbon paste electrode constituted by 25% (w/w) of polyphenol oxidase obtained from Annona muricata L. tissue, 30% (w/w) of graphite, 30% (w/w) of silicone and 15% (w/w) of 7,7,8,8 tetracyanoquinodimethane (TCNQ), was used as flow-through detector. The flow amperometric detection was carried out at a potential of 0.10 V (vs. Ag/AgCl) when an injected sample volume of 250 microl was inserted on a 0.3 M phosphate buffer carrier solution (pH 7.8) flowing at 2.5 ml/min. The developed biosensor showed good stability and reproducibility, enabling up to 500 determinations in 60 days, without considerable loss of enzymatic activity. The FIA system presented a linear response to Do concentrations in the interval from 2 x 10(-2) to 2 x 10(-4) M, with relative standard deviations lower than 1.5%. The kinetic parameter K(M) for the soluble and immobilized enzyme was 1.45 x 10(-2) and 1.91 x 10(-2) M, respectively. In the analyses of different commercially pharmaceutical formulations a relative deviation lower than about 3.4% was obtained.

Flow injection spectrophotometric determination of adrenaline in pharmaceutical formulations using a solid-phase reactor containing lead(IV) dioxide immobilized in a polyester resin

A flow injection spectrophotometric procedure is proposed for determining adrenaline in pharmaceutical formulations. In this work, the adrenaline in acetate buffer reacts with a solid-phase reactor containing lead(IV) dioxide immobilized in a polyester resin and the adrenochrome yielded was continuously monitored at 486 nm. The analytical curve was linear in the adrenaline concentration range from 0.1 to 0.8 mmol l(-1) with a detection limit of 8 x 10(-3) mmol l(-1). Recoveries of 96.5-105% and relative standard deviation of 0.2% for a solution containing 0.4 mmol l(-1) adrenaline (n = 10) were obtained. The analytical frequency was 130 determinations per hour and the results obtained for adrenaline in pharmaceutical formulations using this procedure and those obtained using a pharmacopoeia procedure are in agreement at the 95% confidence level.