Analytical & Bioanalytical Electrochemistry
Volume:4 Issue: 1, Feb 2012

Acetylcholinesterase (AChE) was an important cholinesterase enzyme present in the living organisms, which is responsible for transmission of impulses through synaptic clefts by oxidation of acetylcholine to choline. Acetylcholinesterase enzyme was immobilized through silica sol–gel process on the surface of carbon paste electrode which was used to fabricate monoenzyme biosensor. It is a rapid, simple and sensitive biosensor used for determination of two organophosphorous pesticides monocrotophos and phosphamidon in 0.1 M phosphate buffer and in 0.1 M KCl. Acetylthiocholine chloride (ASChCl) was used as substrate by enzymatic hydrolysis it gives thiocholine which undergone electrochemical oxidation and produces anodic current around at 0.60 V vs. saturated calomel electrode. The effect of scan rate, pH, enzyme loading and substrate concentration on the biosensor response was studied. The biosensor provided a high sensitivity, large linear concentration range from 50–900 ppb, 0.1–1.25 ppm for monocrotophos and phosphamidon. The detection limits were found to be 45 ppb, 0.06 ppm for monocrotophos and phosphamidon respectively. The results showed the optimum conditions for pH, substrate concentration, and incubation time were at room temperature, pH 7.0, 1 mM, 4 and 3 min for monocrotophos and phosphamidon respectively.

The construction and general performance characteristics of potentiometric sensors responsive to some anti-histaminics Hydroxyzine hydrochloride (HYZ), Meclozine hydrochloride (MOZ) were described. The membranes incorporate the ion-association complex of the drugs with Sodium 12-Tungstophosphate (TP) sensor-1, Ammonium Reineckate (AR) senser-2, and Ammonium Molbydate(AM) senser-3as electroactive materials. These sensors exhibit fast, stable, and near-Nernstain response over the concentration range 10-2 to 10-7 M with slopes of 53.07 and 52.14 mV per concentration decade for sensors 1, 2. No interferences are caused by many inorganic and organic cations. The sensors have a fast response time (20-40 s) and applicaple over a wide range of pH 2-7), low detection limit (1.8×10-7 M) and good stability (5-6 weeks).The sensors were used for direct potentiometric of anti-histaminics in some pharmaceutical preparations. Validation of the method according to the quality assurance standards shows suitability of the proposed sensors for use in the quality assurance of these drugs. Results with a recovery of 99.5 % and a mean standard deviations of ±1.3 % of the nominal are obtained which compared fairly well with data obtained using the British pharmacopoeia method.

This paper reports the selective determination of carbidopa (CD) in the presence of uric acid (UA) using 2,7-bis(ferrocenyl ethyl)fluoren-9-one modified carbon nanotube paste electrode (2,7-BFCNPE) in 0.1 M phosphate buffer solution (PBS) pH 7.0. In PBS of pH 7.0, the oxidation current increased linearly with two concentration intervals of CD, one is 0.2 to 22.0 μM and, the other is 22.0 to 750.0 μM. The detection limit (3σ) obtained by DPV was 68.0 nM. The practical application of the modified electrode was demonstrated by determining CD in urine samples.

Novel polymeric membrane electrode based on o-hydroxyacetophenone carbohydrazone (OHAC) as a neutral ionophore carrier has been prepared and explored as silver(I) ion selective electrode. The addition of lipophilic anion excluder (NaTBP) and various plasticizers viz. o-nitrophenyl octyl ether (o-NPOE), dibutyl phthalate (DBP) and butyl acetate (BA) have found to improve the performance of membrane sensor which have a composition of I:NaTBP:NPOE:PVC in the ratio 3:2:62:33 (w/w; mg). The electrode exhibit Nernstian slope for silver (I) ions over wide concentration ranges from 1.0×10-7 M to 1.0×10-2 M with limits of detection 1.6×10-7 M. The response time was found to be 10 s. The potentiometric responses were independent of the pH of the test solutions in the pH range of 3.0 to 8.0. The proposed electrode revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The proposed PVC electrode was used as an indicator electrode in the potentiometric titration of Ag+ ions with KI and NaCl solutions and in direct determination in different water samples and urine sample of peoples working as jewelry maker.

The poly (losartan) film was prepared on the surface of carbon paste electrode by electrochemical method using cyclic voltammetric technique. The poly(losartan) film modified carbon paste electrode was calibrated with standard potassium ferrocyanide solution in 1 M KCl as supporting electrolyte. The prepared poly(losartan) film coated electrode exhibits excellent electrocatalytic activity towards the detection of dopamine at neutral pH. The effect of scan rate, concentration and pH was studied. The overall process was found to be diffusion-controlled.

In this work, a new electrochemical system was developed for determination of cholesterol based on coulometric fast Fourier transformation cyclic voltammetry (CFFTCV) in a flow injection analysis system. In this detection method, also a new cholesterol oxidase biosensor was designed by immobilizing the enzyme into a cross-linked matrix of chitosan– room-temperature ionic liquid (1-butyl-3-methylimidazolium tetra fluoroborate). Initially, the surface of a glassy carbon electrode was modified with CeO2 NPs and then by the electrodeposition of Au particles onto the thiol functionalized multiwalled carbon nanotubes. Scanning electron microscopy and impedance spectroscopy was use to characterize the biosensor. The presence of Au and CeO2 nanoparticles in the matrix of provides an environment for the enhanced electrocatalytic activities. Under optimal conditions, the biosensor exhibited a linear response to cholesterol in the concentration range of 0.01–1 μM with a correlation coefficient of 0.99, good sensitivity, a low response time, repeatability (R.S.D value of 1.9%) and long term stability, 45 days with a decrease of 4% response.

A new superionic mixed composite system, [Cu2HgI4:0.2 AgI]:0.xCuI, (x=0.2, 0.4, 0.6 mol. wt. %), was prepared by conventional solid state reactions and [Cu2HgI4:0.2 AgI] mixed system was used as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100 Hz, 120 Hz, 1 kHz, and 10 kHz in the temperature range 90°-170 °C by a Gen Rad 1659 RLC Digibridge. Conductivity increased sharply during the β-α phase transition. As a result of increase in the dopant-to-host ratio, the conductivity of the system exhibited Arrhenius (thermally activated)-type behavior. The phase transition temperature increased with an increase in the dopant concentration. Activation energies for the system in eV both for the pre-transition and post-transition phase transformations are reported. The addition of CuI to [Cu2HgI4:0.2 AgI] shifted the phase transition of the host [Cu2HgI4:0.2 AgI], due to an interaction between [Cu2HgI4:0.2 AgI] and CuI.

The podand chelate, 1,2-bis[2' -(8" -oxyquinoline)ethoxy]-benzene have been synthesized and used as a neutral ionophore to construct an ion selective electrode for the potentiometric determination of thallium ions. Due to the decisive role of solvent mediators, the membranes was fabricated with the plasticizers o-NPOE, DBP, DBBP, TEP, OA, DOP, CN respectively and anionic additive NaTPB. The best of the results were obtained with the membrane electrode composition of o-NPOE:PVC:Ionophore:NaTPB (58%:34%:5%:3%). This sensor exhibits Nernstian response with slope 58.7±0.3 mV decade-1 of activity in concentration range 2.0×10-9 to 1.0×10-1 M Tl(I), performs satisfactorily over wide pH range (2.5-12), with a fast response time (5 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 40% content of methanol, ethanol, acetone and acetonitrile solution. The Tl(I)-selective electrode was used as an indicator electrode for the titration of TlNO3 with EDTA and KI solution. The selectivity coefficients determined by using fixed interference method (FIM) indicate high selectivity for Tl (I).