Martin Bartoš

AMPEROMETRIC DETERMINATION OF GLUCOSE WITH AN MnO2 AND GLUCOSE OXIDASE BULK-MODIFIED SCREEN-PRINTED CARBON INK BIOSENSOR

A simple biosensor, constructed by bulk-modification of carbon ink with manganese dioxide as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as amperometric detector for glucose in hydrodynamic as well as in flow injection analysis (FIA) mode. The sensor could be operated at a potential of 0.48 V under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited excellent reproducibility and stability. Factors influencing the amperometric response such as injection volume, flow rate and applied working potential were studied in detail. The screen-printed electrode exhibited a linear amperometric increase with the concentration of D-glucose from 2 to 2500 mg L−1 and gave a 3σ detection limit of 0.085 mg L−1. Due to its remarkable stability such a sensor could be operated continuously for more than four weeks or more than 1000 sample injections. No change of signal height could be observed within an operation period of 12 h. The sensor was exploited for FIA-amperometric determination of glucose in beer and wine samples

Trace iron determination in aminoisophthalic acid using differential-pulse cathodic stripping voltammetry at carbon paste electrodes

Application of differential-pulse cathodic stripping voltammetry using a carbon paste electrode (consisting of carbon powder and liquid paraffin) have been investigated for trace determination of iron in 5-aminoisophthalic acid (AIPA). Samples were dissolved in 1 M HC1, pH was adjusted to 4-5 after addition of EDTA. Voltammetric measurements were performed after filtration. No sample decomposition (mineralization) was necessary. The method showed a good linearity between current and concentration from 3 x 10(-7) to 5 x 10(-5) mol dm-3 of iron, with a detection limit of 3 x 10(-7) mol dm-3 (resp. 1 ppm in solid AIPA). The results agreed well to those obtained by atomic absorption spectrometry (AAS) using electrothermic atomisation. For AAS measurement, however, microwave digestion of samples was necessary.

Isotachophoretic determination of hydrosulfite and metabisulfite in technical samples.

A method for determination of metabisulfite and hydrosulfite in poultice and decolorant by isotachophoresis was developed. Metabisulfite and hydrosulfite are ionizable oxoanions of sulfur of similar character that can easily be oxidized to sulfates. To protect the analytes from oxidation the solid samples were dissolved in a 1% (w/v) solution of formaldehyde. Hydrosulfite and metabisulfite present in the samples were transformed by the reaction with formaldehyde to stable compounds, hydroxymethanesulfinate and hydroxymethanesulfonate that were determined isotachophoretically without any pretreatment except for sample filtering and degassing. A capillary of 0.4mm i.d. and 100mm effective length made of fluorinated ethylene-propylene copolymer was filled with an electrolyte system consisting of 10 mmol L(-1) HCl+11 mmol L(-1) imidazole, 0.15% (w/v) hydroxyethylcellulose, pH 6.0 (leading electrolyte) and 5 mmol L(-1) benzoic acid+6 mmol L(-1) imidazole, pH 6.5 (terminating electrolyte). Separation was performed at a driving current of 80 microA and for detection current was decreased to 30 microA. Using contactless conductivity detection, the calibration curves in the tested concentration range up to 2.5 mmol L(-1) were linear for both metabisulfite and hydrosulfite complexes. The concentration detection limits for metabisulfite and hydrosulfite were 2.9 and 3.4 micromol L(-1), respectively. For 1 mmol L(-1) concentration, values of R.S.D. (n=6) were 2.6% for hydrosulfite and 0.8% for metabisulfite. Isotachophoretic determination took about 20 min. The elaborated isotachophoretic procedure is simple to perform, sufficiently sensitive and accurate. In addition to this, low cost of analyses makes the method an alternative procedure to methods used so far for the determination of oxoanions of sulfur.

Formulation and dissolution kinetics study of hydrophilic matrix tablets with tramadol hydrochloride and different co-processed dry binders

The aim of this study is to present the possibility of using of co-processed dry binders for formulation of matrix tablets with drug controlled release. Hydrophilic matrix tablets with tramadol hydrochloride, hypromellose and different co-processed dry binders were prepared by direct compression method. Hypromelloses Methocel™ K4M Premium CR or Methocel™ K100M Premium CR were used as controlled release agents and Prosolv® SMCC 90 or Disintequik™ MCC 25 were used as co-processed dry binders. Homogeneity of the tablets was evaluated using scanning electron microscopy and energy dispersive X-ray microanalysis. The release of tramadol hydrochloride from prepared formulations was studied by dissolution test method. The dissolution profiles obtained were evaluated by non-linear regression analysis, release rate constants and other kinetic parameters were determined. It was found that matrix tablets based on Prosolv® SMCC 90 and Methocel™ Premium CR cannot control the tramadol release effectively for >12h and tablets containing Disintequik™ MCC 25 and Methocel™ Premium CR >8h.

Comparative evaluation of the use of dry binders in a physical mixture or as a coprocessed dry binder in matrix tablets with extended drug release

Abstract This paper evaluates and compares the properties of directly compressible tabletting materials and matrix tablets containing a combination of α-lactose monohydrate and microcrystalline cellulose in the 3:1 ratio in a physical mixture and in a coprocessed dry binder. Tested parameters include flow properties, compressibility, compactibility and the rate of drug release from tablets. Compressibility is evaluated by means of the energy profile of the compression process. Compactibility is evaluated by means of the tensile strength of the tablets. Dissolution testing is done using the rotating basket method. Dissolution profiles are evaluated by non-linear regression analysis. Total energy of compression and plasticity values were higher in tabletting materials with the coprocessed dry binder. Increasing additions of polyvinyl alcohol decreased the values of total energy of compression, plasticity, tensile strength of tablets and drug release rate. Dissolution behaviour of tablets, which contained the physical mixture or coprocessed dry binder and the same amount of polyvinyl alcohol, was comparable.