Molecularly imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) modified glassy carbon electrode as an electrochemical theophylline sensor.

Theophylline is an inexpensive drug employed in asthma and chronic obstructive pulmonary disorder medications and is toxic at higher concentration. The development of a molecularly imprinted polymer based theophylline electrochemical sensor on glassy carbon electrode by the electropolymerization of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid is being discussed in this work. The MIP modification enhances the theophylline recognition ability and the electron transfer kinetics of the bare electrode. The parameters, controlling the performance of the imprinted polymer based sensor, like number of electropolymerization cycles, composition of the pre-polymerization mixture, pH and immersion time were investigated and optimized. The interaction energy and the most stable conformation of the template-monomer complex in the pre-polymerization mixture were determined computationally using ab initio calculations based on density functional theory. The amperometric measurements showed that the developed sensor has a method detection limit of 0.32µM for the dynamic range of 0.4 to 17µM, at optimized conditions. The transducer possesses appreciable selectivity in the presence of structurally similar interferents such as theobromine, caffeine and doxofylline. The developed sensor showed remarkable stability and reproducibility and was also successfully employed in theophylline detection from commercially available tablets.

Molecularly imprinted polymer based electrochemical detection of L-cysteine at carbon paste electrode.

A methacrylic acid (MAA) based molecularly imprinted polymer (MIP) modified carbon paste electrode (CPE) was developed for electrochemical detection of L-cysteine (Cys). Characterisation of MIP was done with FTIR and the modified electrode with cyclic voltammetry (CV) and differential pulse voltammetry (DPV). CV, DPV and impedance analysis demonstrated that the modified electrode is responsive towards the target molecule. The optimum percentage composition of MIP for MIP/CPE and the effect of pH towards the electrode response for Cys were studied. The detection of Cys in the range of 2×10(-8) to 18×10(-8)M at MIP/CPE was monitored by DPV with a limit of detection of 9.6nM and R(2) of 0.9974. Also, various physiological interferents such as ascorbic acid, L-tryptophan, D-glucose, D-cysteine and L-cysteine were found to have little effect on DPV response at MIP/CPE. The utility of the electrode was proved by the effective detection of Cys from tap water and human blood plasma samples with reproducible results.

Determination of toxic heavy metals in sea water by FAAS after preconcentration with a novel chelating resin.

A solid phase extraction procedure was developed for preconcentration of toxic heavy metals such as cadmium, cobalt, copper, manganese, lead and zinc in sea water samples. A microcolumn packed with 6-[(4-hydroxyphenyl)diazenyl]naphthalene-2,3-diol-formaldehyde (HPDN-F) resin acts as a sorbent to retain the analyte ions by forming metal chelates. The retained trace level metal was subsequently eluted with 1 mol/L HCl and the acid eluent was analysed by Flame Atomic Absorption Spectrophotometer (FAAS). The HPDN-F chelating resin and its metal chelates were characterized by spectral and thermal analysis. The chelating property of the HPDN-F resin towards divalent metal ions was studied as a function of pH and preconcentration flow rate. The recoveries of cadmium, cobalt, copper, manganese, lead and zinc under the optimum working conditions were above 95%. The relative standard deviations were < 2%. The limits of detection were < 0.1 microg/L. The method presented was applied for the determination of cadmium, cobalt, copper, manganese, lead and zinc in sea water samples.

Preconcentration of Cu (II) from seawater using a novel and stable phenol-formaldehyde resin.

Preconcentration of Cu (II) from seawater using a novel phenol-formaldehyde (P-F) resin was investigated. 1,2-dihydroxybenzene-4-azo-3-hydroxybenzene-formaldehyde resin (DAHBF) was prepared by condensing 1,2-dihydroxybenzene-4-azo-3-hydroxybenzene with formaldehyde (1:2 mole ratio) in the presence of oxalic acid as catalyst. Polychelates were obtained when the DAHBF was treated with the aqueous solution of Cu (II) ions. The polymeric resin and polymer-metal complexes were characterized with thermal analysis and spectral studies. The IR spectra of polychelates suggest that the metal was coordinated through the oxygen atoms of the dihydroxybenzene moiety. The TGA data revealed the thermal stability of the resin and the polychelates. X-ray diffraction study revealed the incorporation of the metal ion significantly enhanced the degree of crystallinity. The sorption properties of the chelate forming resin towards divalent metal ion [Cu(II)] was studied as a function of pH, preconcentration time, metal concentration, amount of resin, aqueous phase volume and presence of electrolyte. This procedure was validated for recovery of copper from seawater samples. The method has adequate accuracy and it can be used for determination of copper in sea water samples.

Effect of gamma-irradiation of ion imprinted polymer (IIP) particles for the preconcentrative separation of dysprosium from other selected lanthanides.

The selectivity of zinc with respect to copper ions was improved by gamma-irradiation of surface imprinted polymer particles. We have reported the preparation of dysprosium ion imprinted polymer (IIP) particles by covalent approach during molecular imprinting. This paper reports the results obtained after gamma-irradiation of dysprosium IIP particles and their use in the preconcentration/separation of dysprosium from dilute aqueous solutions containing other selected lanthanides. Further, the characterisation of blank and dysprosium IIP particles was carried out either with and without irradiation by IR, thermogravimetric analysis (TGA), differential thermal analysis (DTA), XRD and surface area and pore size analysis techniques. The significant features observed in these experiments in the non-selectivity of blank polymer particles for dysprosium over other lanthanide ions and 35-180-fold enhancement in selectivity coefficients of irradiated dysprosium IIPs formed by covalent approach. In addition, the selectivity coefficients obtainable by gamma-irradiated were compared with unirradiated dysprosium IIP particles and separation factors obtained by liquid-liquid extraction separation using di(2-ethyl hexyl) phosphoric acid as extractant.