Jolanta Kochana

Extended Gran method and its applicability for simultaneous determination of Fe(II) and Fe(III)

Abstract A new extended Gran’s method is proposed and applied for simultaneous determination of iron (II and III) species by potentiometric titration with potassium permanganate solution. Conditions for titrations providing unbiased results of analyses were chosen on the basis of equilibrium analysis (simulated titration).

Tyrosinase-based biosensor for determination of bisphenol A in a flow-batch system

A tyrosinase-based amperometric biosensor is proposed for determination of bisphenol A (BPA) in a flow-batch monosegmented sequential injection system. The enzyme was entrapped in a sol-gel TiO2 matrix modified with multi-walled carbon nanotubes (MWCNTs), polycationic polymer poly(diallyldimethylammonium chloride), (PDDA) and Nafion. Morphology of TYR/TiO2/MWCNTs/PDDA/Nafion matrix composite was studied via scanning electron microscopy (SEM). Electrochemical behavior of the developed biosensor towards bisphenol A was examined and analytical characteristics were assessed with respect to linear range, biosensor sensitivity, limit of detection, long term stability, repeatability and reproducibility. Linear range of biosensor response was found between 0.28 and 45.05 µM with high sensitivity of 3263 µA mM(-1) cm(-2) and detection limit 0.066 µM. The approach was successfully employed for determination of BPA in natural samples.

Tyrosinase biosensor for benzoic acid inhibition-based determination with the use of a flow-batch monosegmented sequential injection system

Amperometric tyrosinase based biosensor for benzoic acid determination with the use of a flow-batch monosegmented sequential injection system is proposed. The functioning of the biosensor is based on the inhibition effect of benzoic acid on the biocatalytic activity of tyrosinase, polyphenol oxidase. In the biosensor, tyrosinase is entrapped in titania gel modified with multiwalled carbon nanotubes (MWCNT) and Nafion. The procedure of optimization of experimental conditions affecting the biosensor response, as well as its analytical characteristics and results of the approach verification using synthetic samples and a reference material are presented. The developed biosensor exhibits linear range up to 2.46μM, good sensitivity toward benzoic acid (1.06μAμM(-1)) and low detection limit (0.03μM). The approach has been applied to benzoic acid determination in a real beverage sample giving the result consistent with that obtained using the HPLC method.

Detection of NADH and ethanol at a graphite electrode modified with titania sol-gel/Meldola's Blue/MWCNT/Nafion nanocomposite film

For electrocatalytic determination of NADH, a graphite electrode modified with titania sol-gel/Meldola’s Blue/MWCNT/Nafion nanocomposite was proposed. The composition of the matrix film was optimised in terms of the content of carbon nanotubes and Nafion. Incorporation of a redox mediator, Meldola’s Blue, into the nanocomposite film enabled electrocatalytic determination of NADH at a low potential, −50 mV. For determination of ethanol, alcohol dehydrogenase (ADH) was immobilized into the matrix layer. Experimental conditions affecting the biosensor response were examined, including enzyme loading, temperature of measurement and pH of background electrolyte. Assessments of the analytical characteristics of the biosensor were performed with respect to sensitivity, limit of detection, operational stability, repeatability and reproducibility. The proposed biosensor showed electrocatalytic activity toward oxidation of ethanol with sensitivity of 2.24 µA L mmol−1, linear range from 0.05 to 1.1 mmol L−1, and limit of detection of 25 µmol L−1. The apparent Michaelis-Menten constant was 1.24 mmol L−1, indicating a high biological affinity of ADH/titania sol-gel/Meldola’s Blue/MWCNT/Nafion electrode for ethanol. The developed biosensor was tested in determinations of ethanol content in alcoholic beverages.

Synthesis of standards of the most important markers of Leuckart p-methoxymethamphetamine (PMMA): Examination of the influence of experimental conditions and a drug diluent on SPE/TLC profiling

The synthesis of characteristic markers of PMMA obtained by Leuckart method was described. The effectiveness of a procedure of SPE/TLC screening profiling of impurities was studied on the basis of selected impurities. The influence of glucose (a drug diluent) on the profile quality was investigated. The intermediate product (characteristic for the Leuckart synthesis) N-formyl-p-methoxymethamphetamine (1) and by-products: N-formyl-p-methoxyamphetamine (2), p-methoxyamphetamine (3), N,N-dimethyl-p-methoxyamphetamine (4), (RS) and (RR/SS) diastereoisomers of bis(1-methyl-2-(4-methoxyphenyl)ethyl)amine (meso-5 and rac-5), (RS) and (RR/SS) diastereoisomers of N-methyl-bis(1-methyl-2-(4-methoxyphenyl)ethyl)amine (meso-6 and rac-6), N-methyl-1,3-bis(4-methoxyphenyl)propane-2-amine (7) were synthesized. The substrate p-methoxyphenylacetone and the impurities 1 and 4 were used in the study of influence of experimental conditions and glucose on the profiling process and results. The experiments were carried out according to a 2(4) factorial design. The proposed criterions of the profile quality are based on matrix presentation of TLC patterns. They take into account the number of spots revealed, differences between R(f) values and intensity of fluorescence, simultaneously.

Meldola’s Blue — doped titania sol-gel sensor for NADH determination

AbstractTitania layers obtained by a sol-gel technique doped with redox mediator, Meldola’s Blue, were employed for construction of a new NADH senor. Optimization of preparation process as well as experimental conditions affecting the response of the sensor were examined. Under optimal conditions NADH could be determined in the wide linear range from 90 to 2300 µM with detection limit 12 µM and a high sensitivity 12.5 nA µM−1. The usefulness of developed sensor was preliminarily checked in determination of NADH forming during enzymatic oxidation of ethanol catalyzed by alcohol dehydrogenase (ADH).

Profiling of impurities in p-methoxymethamphetamine (PMMA) by means of SPE/TLC method: Examination of the influence of experimental conditions according to 24 factorial

In the present paper profiling of impurities in p-methoxymethamphetamine (PMMA) by means of SPE/TLC is reported. PMMA was synthesised by Leuckart procedure. The influence of experimental conditions on the profile quality was investigated. The experiments were carried out according to a 2(4) factorial. The proposed characteristics of the profile quality (optimisation criterions) are based on a matrix presentation of TLC patterns. They take into account, simultaneously, the number of spots revealed, differences between R(f) values and intensity of fluorescence.

Simultaneous spectrophotometric flow injection determination of phosphate and silicate.

A method for the simultaneous determination of phosphate and silicate based on spectrophotometric measurement at 385 nm of a single peak using a flow injection system with two component calibration is described. In the system, a stream of sample containing both analytes is merged with a stream of ammonium molybdate to form (at 1<pH<2) molybdophosphoric and molybdosilicic acids. Total absorbance of the compounds is registered in a form of a constant signal. Simultaneously, oxalic acid solution is injected into a carrier stream (H2SO4) and then merged with the stream of sample containing the mixture of heteropolyacids. A characteristic peak is registered as a result of selective decomposition of molybdophosphoric acid by oxalic acid. The area (or the absorbance measured at the constant signal) and the absorbance measured at the minimum of the peak can be used as measures corresponding to the phosphate and silicate concentrations, respectively. The time of the peak registration is about 3 min. Two-component calibration with the use of four standard solutions of the phosphate/silicate concentrations established in accordance with 2(2) factorial design was applied. Phosphate and silicate can be determined within the concentration ranges of 0.20-15.00 and 0.20-20.00 mg L(-1), with precision less than 2.7 and 0.9% (RSD), respectively and accuracy better than 6.2% (RE). The detection limit is 0.054 and 0.092 mg L(-1) for phosphate and silicate, respectively. The method was applied to determination of the analytes in certified reference materials of groundwater, wastewater, and river water giving results consistent with the certified values.

Study of SPE Conditions for CE Determination of Tricyclic Antidepressants in Body Fluids

Abstract The optimal solid‐phase extraction conditions for six tricyclic antidepressants present in body fluids have been studied. The compounds were separated and detected by capillary electrophoresis with UV spectrophotometry. In the examinations, three sorbents, five pretreatments of body fluids, and four extraction procedures were taken into account. On the basis of preliminary experiments, the best starting conditions were chosen for further optimization of such factors as sorbent mass and volumes of conditioning, washing, and eluent reagents. In the optimized conditions, the average extraction recoveries and their repeatability for all drugs present in whole blood and serum have been evaluated.

Novel electroanalytical method based on the electrostriction phenomenon and its application to determination of Cr(VI) by the flow injection technique

The electrostriction phenomenon is observed in membranes of thickness in the nanometer range, e.g. bilayer lipid membranes or self-assembled monolayers. Strong electrical field of 105-106V/cm in intensity appears when applying the potential lower than 1V to these membranes. Electrostatic forces change the dimensions of a dielectric, hence the membrane compression and decrease in thickness are observed. As a result, increase in the membrane capacitance is recorded. The presented work covers development and application of a new analytical method based on the innovative capacitance-to-frequency conversion method and flow technique. Construction of the novel flow manifold designed for realization of the whole analytical procedure of chromium(VI) determination with the use of capacitance measurements and its operating rules are shown. The main element of the system is a specially designed measurement cell for realization of chromium determination using a three-electrode system. Au electrode with a self-assembled monolayer of thiols grafted with functional groups selectively interacting with the analyte is employed as a dielectric layer. Ag/AgCl electrode and Pt one are used as a reference and auxiliary electrode, respectively. Accuracy, repeatability and reproducibility of the proposed analytical procedure were tested in determination of Cr(VI) in synthetic solutions and environmental water matrices spiked with the analyte. Benefits and drawbacks of the developed manifold were critically discussed.