Martin Bartoš

Tablets used for extended drug release commonly contain large amounts of drugs. The corresponding drug release mechanism thus has to be well-known and invariable under numerous conditions in order to prevent any uncontrolled drug release. Particularly important is the stability and invariability of the release mechanism in the presence of alcohol due to the possible occurrence of the dose dumping effect. The effect of 3D printing (3DP) coating on the drug release mechanism and the drug release rate was studied as a possible tool for the prevention of the alcohol-induced dose dumping effect. Three types of matrix tablets (hydrophilic, lipophilic, and hydrophilic-lipophilic) were prepared by the direct compression method and coated using 3DP. The commercial filament of polyvinyl alcohol (PVA) and the filament prepared from hypromellose by hot melt extrusion (HME) were used as coating materials. Both coating materials were characterized by SEM, DSC, Raman spectroscopy, and PXRD during ...

Summary The aim of the present work was to investigate a new mechanism likely contributing to the toxic action of acetaminophen especially to explore the possible inhibition of glutathione reductase through an acetaminophen-glutathione conjugate (APAP-SG). APAP-SG conjugate was synthesized by organic synthesis and purified by column chromatography. The inhibitory effect of the conjugate on two types of glutathione reductase (from yeasts and rat hepatocytes) was tested spectrophotometrically. We found that the enzyme activity was reduced similarly after treatment with 2.96 mM acetaminophen-glutathione conjugate in both yeast and hepatocyte glutathione reductases (GR); the enzyme activity was inhibited to 52.7 ± 1.5 % (2.4 ± 0.3 mU/ml) in yeast GR (control activity was 5.6 ± 0.3 mU/ml) and to 48.1 ± 8.8 % (2.2 ± 0.2 mU/ml) in rat hepatocytes lysate GR (control activity was 5.2 ± 0.2 mU/ml). In addition, the enzyme activity (from hepatocytes lysate) was decreased to 79±7 %, 67±2 % and ...

In this article, hexamine (HX; syn.: urotropine, chem.: 1,3,5,7tetraaza-tricyclo [3.3.1.1]decane, C6H12N4) is the analyte of interest determined in commercially marketed fungicide (Dithane DG) with the aid of capillary isotachophoresis. After method development, the optimal electrolyte system comprised 0.01 M KOH + 0.02 M acetic acid + 0.1 % hydroxyethylcellulose (pH 4.75) as the leading electrolyte and 0.01 M acetic acid as the terminator. The calibration / detection characteristics are as follows: linearity over the concentration range of 0– 200 mg.l HX, limit of detection ca. 2 mg.l, limit of quantification of ca. 6 mg.l HX. Furthermore, relatively simple procedure (involving extraction as the only major sample pretreatment), low operational costs, and sufficient sensitivity are also typical attributes of the method that can be recommended for analysis of hexamine in herbicides and related samples.

In this contribution, groove electrodes (GrEs) are presented as a new type of carbon paste electrodes (CPEs). The GrEs are designed as a mountable kit based on plastic prismatic bars (40×10×2mm) with horizontal channel for carbon paste filling, metal contact, and additional plastic inserts defining the electrode surface area. Compared to conventional CPEs, construction specifics of GrEs offer simpler preparation

We report on possible use of wood-free resin pencil (WPE) as low-cost pH electrode based on WPE coated by antimony or bismuth film as the main pH sensitive material. Sensors prepared allowed to measure pH in the range of 3-10 and 10-13. The pH electrodes proposed can take advantage in strong alkaline and corrosive systems where the use of traditional glass electrode is limited. Also, they can serve as the low-cost indicator electrodes in acid-base titrations.

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, whic...

The aim of the present work was to investigate a new mechanism likely contributing to the toxic action of acetaminophen, especially to explore the possible inhibition of glutathione reductase through an acetaminophen-glutathione conjugate (APAP-SG). APAP-SG conjugate was synthesized by organic synthesis and purified by column chromatography. The inhibitory effect of the conjugate on two types of glutathione reductase (from yeasts and rat hepatocytes) was tested spectro-photometrically. We found that the enzyme activity was reduced similarly after the treatment with 2.96 mM acetaminophen-glutathione conjugate in both yeast and hepatocyte glutathione reductases (GR); the enzyme activity was inhibited to 52.7+/-1.5 % (2.4+/-0.3 mU/ml) in yeast GR (control activity was 5.6+/-0.3 mU/ml) and to 48.1+/-8.8 % (2.2+/-0.2 mU/ml) in rat hepatocytes lysate GR (control activity was 5.2+/-0.2 mU/ml). In addition, the enzyme activity (from hepatocytes lysate) was decreased to 79+/-7 %, 67+/-2 % an...

We report on possible use of wood-free resin pencil (WPE) as low-cost pH electrode based on WPE coated by antimony or bismuth film as the main pH sensitive material. Sensors prepared allowed to measure pH in the range of 3-10 and 10-13. The pH electrodes proposed can take advantage in strong alkaline and corrosive systems where the use of traditional glass electrode is limited. Also, they can serve as the low-cost indicator electrodes in acid-base titrations.

A method for isotachophoretic determination of sweeteners of different character in candies and chewing gums was developed. A capillary of 0.8 mm ID and 90 mm effective length made of fluorinated ethylene-propylene copolymer is filled with an electrolyte system consisting of 10 mM HCl + 14 mM Tris, pH 7.7 (leading electrolyte) and 5 mM L-histidine + 5 mM Tris, pH 8.3 (terminating electrolyte). The analysis is performed at a driving current of 200 microA and for detection current is decreased to 100 microA. Boric acid is added to the aqueous sample solution to form borate complexes with substances of polyhydroxyl nature and make them migrate isotachophoretically. Using conductivity detection, the calibration curves in the tested concentration range up to 2.5 mM were linear for all components of interest: acesulfame K, saccharine, aspartame, cyclamate, sorbitol, mannitol, lactitol, and xylitol. The concentration detection limits ranged between 0.024 and 0.081 mM. Good precision of the ITP method is evidenced by favorable RSD values ranging from 0.8 to 2.8% obtained at the analyte concentration of 1.0 mM (n = 6). The analysis time was about 20 min. Simplicity, accuracy, and low cost of analyses make ITP an alternative procedure to methods used so far for the determination of ionizable sweeteners.

Abstract Recently designed and synthetized mono-imidazolinone (I and III) and bisimidazolinone (II and IV) chelating ligands were electrochemically characterized at mercury and carbon paste electrodes. Based on polarographic, voltammetric and ...

A new analytical method for the indirect determination of trace amounts of aluminium(III) is based on the adsorptive accumulation of an azo dye, Arsenazo III, on the hanging mercury drop electrode. In the presence of Al(III) forming complexes with the dye, its peak occurring at -330 mV decreases. Optimized experimental conditions were found as follows: supporting electrolyte, acetate or chloroacetate-acetate buffer (pH 3.6); accumulation potential, -50 mV vs SCE; accumulation time, 120 s; Arsenazo III concentration, 5 · 10-7 mol l-1; scan rate, 20 mV s-1; initial potential, -500 mV; final potential, 0 mV; FSDPV mode; pulse amplitude, 50 mV; pulse duration, 100 ms; pulse interval, 10 ms. Under these experimental conditions, the calibration dependence was linear in the concentration range 0-6 μmol l-1 with a detection limit of 3.7 · 10-8 mol l-1 (1 ppb, calculated as 3σ for n = 10). Interference of iron(III) can be suppressed by addition of L-ascorbic acid, the effect of numerous diva...

A simple glucose biosensor has been developed by bulk modification of a carbon paste electrode with glucose oxidase as a biocomponent and manganese dioxide as a mediator. The sensor was employed as amperometric detector in a flow-injection system at 21 °C in 0.2 M phosphate buffer (pH 7.5). At an applied working potential of 0.48 V vs Ag/AgCl and a flow rate of 0.2 ml min-1, the sensor exhibited well reproducible amperometric response to glucose. A linear relation between the peak current and the analyte concentration was found between 20 and 500 mg l-1 glucose with a detection limit (3σ) of 10.5 mg l-1 glucose. The sensor can be operated continuously for 12 h without any loss in the signal height and can be used for the determination of glucose in white wine samples.

In this article, some new approaches to characterize the carbon paste mixtures and the respective carbon paste electrodes (CPEs) are presented, discussed, and critically evaluated. Particular attention has been paid to the changes of the ohmic resistance, relative to the dependence on composition of the CPE, the materials used, the time, and the position of storage. Four types of carbon pastes were examined, and for the interpretation of experimental data, a new simple model of "close-packing of spheres" has been applied. This model resembles the percolation theory for solid matter. In our case, however, it is possible to explain not only the "bent" or "broken" shape of the dependence of the electrode resistance upon the binder:carbon ratio and the corresponding electrochemical current response, but also differences caused by various material used and three various effects observed during the electrode aging. Furthermore, the report presents the significance of practical utilization of the recently introduced carbon paste index (denoted as chi(CPE)), which is a qualitative hitherto unused factor based on the evaluation of cyclic voltammograms for standard redox systems (e.g., [Fe(CN)(6)](3-/4-)) and specifying the electrochemical properties of a CPE. Some problems connected with homogeneity and stability of carbon pastes, their handling, storage, or eventual aging effects are also discussed.