Geographical origin discrimination of Ethiopian sesame seeds by elemental analysis and chemometric tools.

Origin discrimination of sesame seeds is becoming one of the important factors for the sesame seed trade in Ethiopia as it influences the market price. This study was undertaken to construct accurate geographical origin discriminant models for Ethiopian sesame seeds using multi-element analysis and statistical tools. The concentration of 12 elements (Na, Mg, Cr, Mn, Fe, Cu, Co, Ni, Zn, Cd, As and Pb) were determined in 93 samples which were collected from three main sesame seed-producing regions in Ethiopia, Gondar, Humera and Wollega. According to a one-way analysis of variance (ANOVA), the concentration of 10 elements showing a significant difference (p < 0.05) was taken for statistical analysis using principal component analysis (PCA) and linear discriminant analysis (LDA). PCA showed some clustering of samples according to their respective origins. Then, the follow-up LDA resulted in a 100 % correct origin classification rate for all 93 sesame seed samples obtained from three regions in Ethiopia.

Synthesis of a novel diaquabis(1,10-phenanthroline)copper(II)chloride complex and its voltammetric application for detection of amoxicillin in pharmaceutical and biological samples.

A one step facile synthesis of the novel diaquabis(1,10-phenanthroline)copper(II)chloride (A2P2CuC) complex is demonstrated. Cyclic voltammetric and electrochemical impedance spectroscopic results revealed potentiodynamic deposition of a conductive electroactive poly(A2P2CuC) film on the glassy carbon electrode surface increasing its effective surface area. In contrast to the unmodified glassy carbon electrode, appearance of an oxidative peak at a reduced potential with over two fold current for amoxicillin at poly(A2P2CuC)/GCE demonstrated its electrocatalytic property attributed to reduce charge transfer resistance and the improved surface area of the electrode surface. Better correlation of the oxidative peak current with square root of scan rate (R2 = 0.99779) than with scan rate (R2 = 0.96953) supplemented by slope of 0.58 for log(current) versus log(scan rate) confirmed diffusion controlled irreversible oxidation of amoxicillin. At optimized solution and SWV parameters, current response of poly(A2P2CuC)/GCE showed linear dependence on concentration of amoxicillin (2.0-100.0 µM) with LoD 0.0115 µM. While no amoxicillin was detected in the human blood serum sample, an amount 89.40-100.55% of the nominal level was detected in the analyzed eight tablet brands. Spike recovery in tablet samples (98.90-101.95%) and blood serum sample (102.20-101.37%); interference with an error (%RSD) of 0.00-4.51% in tablet and 0.00-2.10% in serum samples; excellent stability and reproducible results, added with the wide dynamic range and low LoD validated the method for amoxicillin determination in pharmaceutical formulations and human urine samples.

Potentiodynamic Poly(resorcinol)-Modified Glassy Carbon Electrode as a Voltammetric Sensor for Determining Cephalexin and Cefadroxil Simultaneously in Pharmaceutical Formulation and Biological Fluid Samples.

This study covers the development of a fast, selective, sensitive, and stable method for the simultaneous determination of cephalosporins (cephalexin (CLN) and cefadroxil (CFL)) in biological fluids and tablet samples using potentiodynamic fabrication of a poly(resorcinol)-modified glassy carbon electrode (poly(reso)/GCE). The results of cyclic voltammetry and electrochemical impedance spectroscopy supported the modification of the GCE by a polymer layer that raised the electrode surface area and conductivity. At the poly(reso)/GCE, an irreversible oxidative peak with four- and fivefold current enhancement for CLN and CFL, respectively, at a substantially lower potential demonstrated the catalytic action of the modifier. Under optimized solution and parameters, the peak current response at the poly(reso)/GCE revealed a linear dependence on the concentration of CLN and CFL within the range 0.1-300 and 0.5-300 µM, respectively, with a limit of detection (LoD) of 3.12 and 8.7 nM, respectively. The levels of CLN in four selected tablet brands and CFL in two tablet brands were in the vicinity of 91.00-103.65% and 97.7-98.83%, respectively, of their nominal values. The recovery results for CLN in pharmaceutical samples were in the range of 99.00-100.67% and for CFL 97.9-99.75% and for blood serum and urine samples 99.55-100.55% and 99.33-100.34% for CLN and 97.13-100.60% and 96.73-102.50% for CFL, respectively. Interference recovery results with errors less than 4.81%, lower LoD, wider dynamic range, excellent recovery results, and good stability of the modifier compared to those for the previously reported methods validated the use of the poly(reso)/GCE for determining CLN and CFL simultaneously in various real samples.

The conservation of IAP-like proteins in fungi, and their potential role in fungal programmed cell death.

Programmed cell death (PCD) is a tightly regulated process which is required for survival and proper development of all cellular life. Despite this ubiquity, the precise molecular underpinnings of PCD have been primarily characterized in animals. Attempts to expand our understanding of this process in fungi have proven difficult as core regulators of animal PCD are apparently absent in fungal genomes, with the notable exception of a class of proteins referred to as inhibitors of apoptosis proteins (IAPs). These proteins are characterized by the conservation of a distinct Baculovirus IAP Repeat (BIR) domain and animal IAPs are known to regulate a number of processes, including cellular death, development, organogenesis, immune system maturation, host-pathogen interactions and more. IAP homologs are broadly conserved throughout the fungal kingdom, but our understanding of both their mechanism and role in fungal development/virulence is still unclear. In this review, we provide a broad and comparative overview of IAP function across taxa, with a particular focus on fungal processes regulated by IAPs. Furthermore, their putative modes of action in the absence of canonical interactors will be discussed.

EDTA salt modified carbon paste electrode for square wave voltammetric determination of theophylline in pharmaceutical tablet formulation.

In this study, a square wave voltammetric method for determination of theophylline in tablet formulation based on EDTA salt modified carbon paste electrode is presented. CV, FT-IR, and EIS results confirmed modification of the carbon paste with EDTA salt. In contrast to the unmodified carbon paste electrode, the modified carbon paste electrode showed irreversible oxidation of theophylline with considerable current enhancement. Investigation of the effect of scan rate on the Ip and Ep response of the modified electrode for theophylline revealed predominantly diffusion controlled oxidation kinetics. Under the optimized conditions, square wave oxidative peak current of theophylline in pH 7.0 PBS showed linear dependence on concentration in the range 10-200 µM with determination coefficient (R2), limit of detection, and limit of quantification of 0.99782, 0.0257 µM, and 0.0857 µM, respectively. Detection of an amount of theophylline in the analyzed tablet formulation with 1.85% error from its nominal content (120 mg/tablet) confirmed the accuracy of the developed method. Spike and interference recovery results of 98.59%, and 95.7-100%, respectively validated the applicability of the developed method for determination of theophylline content in tablet samples.

Poly(4-amino-3-hydroxynaphthalene-1-sulfonic acid) modified glassy carbon electrode for square wave voltammetric determination of amoxicillin in four tablet brands.

BACKGROUND: Amoxicillin (AMX), which is one of the ß-lactam antibiotics used in the treatment of bacterial infections, is known to have a serious mechanism of resistance necessitating continuous monitoring of its level in pharmaceutical and serum samples. RESULTS: In this study, we presented selective, accurate, and precise square wave voltammetric method based on poly(4-amino-3-hydroxynaphthalene-1-sulfonic acid) modified glassy carbon electrode (poly(AHNSA/GCE)) for determination of amoxicillin in four selected tablet brands. Appearance of a peak in the oxidative scan direction without a peak in the reductive direction of cyclic voltammograms of both bare GCE and poly(AHNSA/GCE) with four folds current and much reduced potential on the modified electrode showed catalytic property of the modifier towards oxidation of AMX. While cyclic voltammetric studies of effect of scan rate showed predominantly diffusion controlled oxidation of AMX with one electron participation, effect of pH revealed participation of protons and electrons in a 1:1 ratio. The square wave voltammetric peak current response of the modified electrode for AMX showed linear dependence on the concentration of the spiked standard AMX in the range 10-150 µmol L-1 with 9.9 nmol L-1 LOD. The AMX content of the studied tablet brands were found in the range 97.84-100.78% of the labeled value. Spike recovery results of 99.6-100.5%, and interference recovery results of 95.4-100.8% AMX in the presence of 50-200% of ampicillin and cloxicillin validated the applicability of the method for determination of amoxicillin in tablet formulation. CONCLUSION: In contrast to the previously reported works on determination of amoxicillin, the present method showed an excellent performance making it a potential method for determination of amoxicillin in real samples including serum samples.

Poly(alizarin red S) modified glassy carbon electrode for square wave adsorptive stripping voltammetric determination of metronidazole in tablet formulation.

Potentiodynamically fabricated poly(alizarin red s) modified GCE was characterized using CV and EIS techniques. In contrast to the cyclic voltammetric response of the unmodified GCE for metronidazole, an irreversible reduction peak with three-folds of current enhancement and reduced overpotential at the poly(alizarin red s) modified GCE showed the catalytic effect of the modifier towards reduction of metronidazole. While observed peak potential shift with increasing pH (4.0-10.0) indicated the involvement of protons during the reduction of metronidazole, peak potential shift with scan rate (20-300 mV s-1) confirmed the irreversibility of the reduction reaction of metronidazole at the modified GCE. A better correlation for the dependence of peak current on scan rate (r2 = 0.9883) than on square root of scan rate (r2 = 0.9740) supplemented by slope value of 0.38 for plot of log(current) versus log(scan rate) indicated the reduction reaction of metronidazole at the surface of the modified electrode was predominantly adsorption controlled. Under the optimized method and solution parameters, reductive current response of tablet sample showed linear dependence on spiked standard concentration in a wide range (0-125 µM) with excellent determination coefficient r2, LoD and LoQ of 0.9991, 0.38, and 1.25 µM, respectively. Spike recovery of 97.9% and interference recovery of 96.2-97.5% in the presence of 21.28 and 31.92 µM of uric acid and ascorbic acid validated the applicability of the present method for determination of metronidazole in tablet formulation. The metronidazole content of the tested tablet formulation using standard addition method was found to be 97.6% of what is claimed by the tablet manufacturer making the developed method an excellent potential candidate for its applicability to determine metronidazole in real samples with complex matrix.

Green synthesized silver nanoparticle modified carbon paste electrode for SWAS voltammetric simultaneous determination of Cd(II) and Pb(II) in Bahir Dar Textile discharged effluent.

The principal objective of this research was to demonstrate the sensitivity and selectivity of carbon paste electrode modified with Ocimum Sanctum leaf extract synthesized silver nanoparticles for simultaneous determination of Cd(II) and Pb(II) in discharged textile effluent. While UV-Vis, XRD and FT-IR were used to fully characterize the green synthesized silver nanoparticles, cyclic voltammetry was used to evaluate the electrochemical behavior of the two metals at the modified electrode relative to the unmodified electrode. Square wave anodic stripping (SWAS) voltammetric current showed linear dependence on the concentration in the range 5-160 ppm with determination coefficients (R2) of 0.9976 and 0.9996 for Cd(II) and Pb(II), respectively. The method also showed extremely low detection limit (0.0891ppm for Cd(II) and 0.048 ppm for Pb(II)) making the method superior over the previously reported methods. Recovery results of 94.3 for Cd(II) and 101.0% for Pb(II) validated the applicability of the method for simultaneous determination of the two metals in a complex matrix textile effluent sample. While levels of Pb(II) and Cd(II) in the untreated sample were 117.0 and 128.3 ppm, their levels in the treated sample were 17.7 and 101.4 ppm, respectively confirming the low efficiency of the treatment plant the factory claims to have. The level of the studied metals in the discharged effluent is much higher than the permissible limit indicating extent of pollution of the water system to which the effluent is discharged.

Adsorptive stripping voltammetric determination of Tetracycline in pharmaceutical capsule formulation using Poly(Malachite green) modified glassy carbon electrode.

A selective and sensitive electrochemical method based on glassy carbon electrode modified with poly(malachite green) was developed for determination of tetracycline in pharmaceutical capsule formulation. Cyclic voltammetry and electrochemical impedance spectroscopy using [Fe(CN)6]3-/4- as a probe were used to characterize the potentiodynamiclly deposited poly(malachite green) on the surface of glassy carbon electrode. In contrast to the unmodified glassy carbon electrode, the fabricated poly(malachite green) modified glassy carbon electrode showed catalytic property towards two steps irreversible oxidation of tetracycline. Better correlation of the oxidative peak current with the scan rate than with the square root of scan rate supported by slope of 0.60 for log(current) versus log(scan rate) indicated that the oxidation reaction of tetracycline at the modified electrode was predominantly controlled by electron exchange step at the solution polymer interface. Under optimized solution pH, and accumulation parameters, the square wave adsorptive anodic striping peak current response of the modified electrode showed linear dependence on concentration of tetracycline in the range 5-100 µM with determination coefficient, method detection limit, and quantification limit of 0.99588, 1.6 µM, and 5.3 µM, respectively. The tetracycline content of a capsule sample claimed to have 250 mg/capsule was found to be 250.53 mg/capsule with 0.21% deviation. Excellent spike recovery result of 99.80%, and 98.49-99.78% recovery of tetracycline in capsule sample in the presence of 50-200% of UA, AA, and ampicillin validated the applicability of the method for determination of tetracycline in real samples with complex matrix like capsule formulations.

Electrochemical Characterization of Iron (III) Doped Zeolite-Graphite Composite Modified Glassy Carbon Electrode and Its Application for AdsASSWV Determination of Uric Acid in Human Urine.

Iron (III) doped zeolite/graphite composite modified glassy carbon electrode was prepared for determination of uric acid in human urine samples. Electrochemical impedance spectroscopic and cyclic voltammetric results confirmed surface modification of the surface of glassy carbon electrodes. Appearance of oxidative peak current with an over threefold enhancement at significantly reduced overpotential for uric acid at the composite modified electrode relative to the unmodified and even graphite modified electrode confirmed the electrocatalytic property of the composite towards electrochemical oxidation of uric acid. Under optimized method and solution parameters, linear dependence of peak current on uric acid concentration in a wide range of 1-120 µM, low detection limit value (0.06 µM), replicate results with low RSD, and excellent recovery results (96.61-103.45%) validated the developed adsorptive anodic stripping square wave voltammetric (AdsASSWV) method for determination of uric acid even in aqueous human urine samples. Finally, the developed composite modified electrode was used for determination of uric acid content in human urine samples collected from three young male volunteers. While the uric acid level in the urine samples from two of the studied volunteers was within the normal range, of the third was under the normal range.

Voltammetric determination of paracetamol in tablet formulation using Fe (III) doped zeolite-graphite composite modified GCE.

Although paracetamol is known to have excellent safety profile at recommended therapeutic doses, health effects are also reported at acute overdoses. A sensitive and selective voltammetric method using Fe(III) encapsulated zeolite/graphite composite modified glassy carbon electrode is presented in this work for the determination of paracetamol in tablet formulations. In contrast to the unmodified electrode, a fourfold increase of cyclic voltammetric oxidative peak current paralleled by reduced potential difference (ΔE p ) at the modified electrode confirmed electrocatalytic property of the modifier towards oxidation of paracetamol. The oxidative peak current showed linear dependence on concentration range 0.5-200 µM with R 2 and LOD of 0.9989 and 0.01 µM, respectively. The paracetamol content of four brands of tablet samples was found in the range 95.95 ± 0.23-103 ± 0.52% of the theoretical values. Recovery results between 94.54 ± 0.82 and 102 ± 0.34% for spiked paracetamol in tablet samples validated the selectivity of the method for determination of paracetamol in real samples.

Comparative Assessment on Selected Physicochemical Parameters and Antioxidant and Antimicrobial Activities of Honey Samples from Selected Districts of the Amhara and Tigray Regions, Ethiopia.

The composition and properties of natural honeys differ with plant species on which the bees forage and the climatic conditions of the production areas. In Ethiopia, Amhara and Tigray are neighboring regions consisting of different agricultural activities and blossoms from different types of vegetations which may influence the natural composition and hence the properties of honey. So, the aim of the current study was to assess the quality of honey from selected districts of the two regions. In the study, 18 composited honey samples were collected from six selected districts and analyzed for selected physicochemical parameters and antioxidant and antimicrobial activities. The analyses of physicochemical parameters were carried out following standard procedures of IHC and QSAE. The antioxidant activity was determined by analyzing the RSA using DPPH while the antibacterial activities were determined by the agar well diffusion method. The moisture, ash content, electrical conductivity, pH, free acidity, reducing sugar, and sucrose content of the honey samples were found to be in the range 16.34 ± 0.26 to 19.83 ± 0.43 %, 0.08 ± 0.00 to 0.45 ± 0.03 %, 0.19 ± 0.00 to 0.89 ± 0.03 mS/cm, 3.79 ± 0.04 to 4.20 ± 0.01, 19.56 ± 1.13 to 38.11 ± 1.54 meq/kg, 62.10 ± 0.48 to 66.37 ± 0.20 %, and 1.35 ± 0.08 to 5.96 ± 0.10 %, respectively. The total phenolic content ranged from 1165.60 ± 23.45 to 1854.83 ± 10.47 mg/kg with antioxidant activity of 21.64 ± 0.26 to 36.12 ± 0.52 AEAC/100 g. The total phenolic contents showed strong correlation with RSA. Furthermore, all honey samples showed an antibacterial activity varying from 23.23 ± 0.12 to 28.84 ± 0.24 mm.

Differential pulse voltammetric determination of salbutamol sulfate in syrup pharmaceutical formulation using poly(4-amino-3-hydroxynaphthalene sulfonic acid) modified glassy carbon electrode.

A new method for determination of salbutamol sulfate has been developed using poly(4-amino-3-hydroxynaphthalene sulfonic acid/GCE. Cyclic voltammetric investigation of the electrochemical behavior of salbutamol sulfate at the polymer modified glassy carbon unveiled electrocatalytic activity of the modifier towards irreversible oxidation of salbutamol sulfate. Dependence of peak current predominantly on scan rate than on square root of scan rate, and peak potential shift with pH demonstrated that oxidation of salbutamol sulfate at the polymer modified electrode follows adsorption reaction kinetics with proton participation. Under optimized solution and differential pulse voltammetric parameters, the oxidative peak current showed linear dependence on salbutamol sulfate concentration in the range 0.2 to 8 µM with method detection limit (3s/m) and determination coefficient (R2) of 6.8 × 10-8 M and 0.99786, respectively. Low method detection limit, relatively wide linear range, and recovery results of spiked standard salbutamol sulfate in syrup samples in the range 96.7-98.9% validated the method for determination of salbutamol sulfate in pharmaceutical formulations. Differential pulse voltammetric analysis of salbutamol sulfate syrup formulation for its salbutamol sulfate content revealed 98.8 to 99.3% of the labeled value confirming the applicability of the developed method for determination of salbutamol sulfate in real samples.

Electrochemical Determination of Caffeine Content in Ethiopian Coffee Samples Using Lignin Modified Glassy Carbon Electrode.

Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6 × 10-6 to 100 × 10-6 mol L-1 with determination coefficient and method detection limit (LoD = 3 s/slope) of 0.99925 and 8.37 × 10-7 mol L-1, respectively, supplemented by recovery results of 93.79-102.17% validated the developed method. An attempt was made to determine the caffeine content of aqueous coffee extracts of Ethiopian coffees grown in four coffee cultivating localities (Wonbera, Wolega, Finoteselam, and Zegie) and hence to evaluate the correlation between users preference and caffeine content. In agreement with reported works, caffeine contents (w/w%) of 0.164 in Wonbera coffee; 0.134 in Wolega coffee; 0.097 in Finoteselam coffee; and 0.089 in Zegie coffee were detected confirming the applicability of the developed method for determination of caffeine in a complex matrix environment. The result indicated that users' highest preference for Wonbera and least preference for Zegie cultivated coffees are in agreement with the caffeine content.

Electrochemical Determination of Metronidazole in Tablet Samples Using Carbon Paste Electrode.

Cyclic voltammetric investigation of metronidazole at carbon paste electrode revealed an irreversible reduction peak centered at about -0.4 V. Observed peak potential shift with pH in the range 2.0 to 8.5 indicated the involvement of protons during the reduction of metronidazole, whereas the peak potential shift with scan rate in the range 10-250 mV/s confirmed the irreversibility of the reduction reaction. A better correlation coefficient for the dependence of peak current on the scan rate than on the square root of scan rate indicated an adsorption controlled kinetics. Under the optimized method and solution parameters, an excellent linearity between the reductive peak current and the concentration of metronidazole was observed in the concentration range 1.0 × 10(-6) to 5.0 × 10(-4) M with a correlation coefficient, method detection limit (based on s = 3σ), and limit of quantification of 0.999, 2.97 × 10(-7) M and 9.91 × 10(-7) M, respectively. Good recovery results for spiked metronidazole in tablet samples and selective determination of metronidazole in tablet formulations in the presence of selected potential interferents such as rabeprazole, omeprazole, and tinidazole confirmed the potential applicability of the developed method for the determination of metronidazole in real samples like pharmaceutical tablets.

Global survey of canonical Aspergillus flavus G protein-coupled receptors.

G protein-coupled receptors (GPCRs) are transmembrane receptors that relay signals from the external environment inside the cell, allowing an organism to adapt to its surroundings. They are known to detect a vast array of ligands, including sugars, amino acids, pheromone peptides, nitrogen sources, oxylipins, and light. Despite their prevalence in fungal genomes, very little is known about the functions of filamentous fungal GPCRs. Here we present the first full-genome assessment of fungal GPCRs through characterization of null mutants of all 15 GPCRs encoded by the aflatoxin-producing fungus Aspergillus flavus. All strains were assessed for growth, development, ability to produce aflatoxin, and response to carbon sources, nitrogen sources, stress agents, and lipids. Most GPCR mutants were aberrant in one or more response processes, possibly indicative of cross talk in downstream signaling pathways. Interestingly, the biological defects of the mutants did not correspond with assignment to established GPCR classes; this is likely due to the paucity of data for characterized fungal GPCRs. Many of the GPCR transcripts were differentially regulated under various conditions as well. The data presented here provide an extensive overview of the full set of GPCRs encoded by A. flavus and provide a framework for analysis in other fungal species. Importance: Aspergillus flavus is an opportunistic pathogen of crops and animals, including humans, and it produces a carcinogenic toxin called aflatoxin. Because of this, A. flavus accounts for food shortages and economic losses in addition to sickness and death. Effective means of combating this pathogen are needed to mitigate its deleterious effects. G protein-coupled receptors (GPCRs) are often used as therapeutic targets due to their signal specificity, and it is estimated that half of all drugs target GPCRs. In fungi such as A. flavus, GPCRs are likely necessary for sensing the changes in the environment, including food sources, developmental signals, stress agents, and signals from other organisms. Therefore, elucidating their functions in A. flavus could identify ideal receptors against which to develop antagonists.

Determination of fenitrothion in water using a voltammetric sensor based on a polymer-modified glassy carbon electrode.

A glassy carbon electrode (GCE) modified with poly(4-amino-3-hydroxynaphthalene sulfonic acid) (poly-AHNSA) was used for the selective and sensitive determination of fenitrothion (FT) organophosphorus pesticide in water. The electrochemical behavior of FT at the bare GCE and the poly-AHNSA/GCE were compared using cyclic voltammetry. Enhanced peak current response and shift to a lower potential at the polymer-modified electrode indicated the electrocatalytic activity of the polymer film towards FT. Under optimized solution and method parameters, the adsorptive stripping square wave voltammetric reductive peak current of FT was linear to FT concentration in the range of 0.001 to 6.6 x 10(-6) M, and the LOD obtained (3delta/m) was 7.95 x 10(-10) M. Recoveries in the range 96-98% of spiked FT in tap water and reproducible results with RSD of 2.6% (n = 5) were obtained, indicating the potential applicability of the method for the determination of trace levels of FT in environmental samples.

Molecular mechanisms of Aspergillus flavus secondary metabolism and development.

The plant and human opportunistic fungus Aspergillus flavus is recognized for the production of the carcinogen aflatoxin. Although many reviews focus on the wealth of information known about aflatoxin biosynthesis, few articles describe other genes and molecules important for A. flavus development or secondary metabolism. Here we compile the most recent work on A. flavus secondary metabolite clusters, environmental response mechanisms (stress response pathways, quorum sensing and G protein signaling pathways) and the function of the transcriptional regulatory unit known as the Velvet Complex. A comparison to other Aspergilli reveals conservation in several pathways affecting fungal development and metabolism.

Polymer-modified glassy carbon electrode for the electrochemical detection of quinine in human urine and pharmaceutical formulations.

Glassy carbon electrode was modified by electropolymerization of 4-amino-3-hydroxynaphthalene sulfonic acid. Cyclic voltammetric study of quinine showed higher current response at the modified electrode compared to the bare and activated glassy carbon electrodes in pH 7.0 phosphate buffer solution. Under optimized conditions, a calibration curve was obtained by square wave voltammetry at the modified electrode. The linear relationship between the peak current and the concentration of quinine in the range of 1.0 × 10(-7) to 1.0 × 10(-5) M was I (pa) (in microamperes) = 6.26C (in micromolars) + 0.2997 (R (2) = 0.999). The detection limit calculated (S/N = 3) was 1.42 × 10(-8) M, which is much lower than similar reports. The method was successfully applied for the determination of quinine in spiked human urine, and pharmaceutical formulations and recovery values >90 % were obtained.

Polymer modified glassy carbon electrode for the electrochemical determination of caffeine in coffee.

4-Amino-3-hydroxynaphthalene sulfonic acid (AHNSA) was electropolymerized on a glassy carbon electrode. The deposited film showed electrocatalytic activity towards the oxidation of caffeine. The polymer-modified electrode showed high sensitivity, selectivity and stability in the determination of caffeine in coffee. The peak current increased linearly with the concentration of caffeine in the range of 6 × 10(-8) to 4 × 10(-5) mol L(-1), with a detection limit of 1.37 × 10(-7) mol L(-1) (LoD = 3δ/slope). Analysis of caffeine in coffee was affected neither by sample matrices nor by structurally similar compounds. Recoveries ranging between 93.75 ± 2.32 and 100.75 ± 3.32 were achieved from coffee extracts indicating the applicability of the developed method for real sample analyses.