Katarína Hroboňová

Simultaneous determination of caffeine, caramel and riboflavin in cola-type and energy drinks by synchronous fluorescence technique coupled with partial least squares

The aim of this work was to develop a multivariate method for the rapid determination of caffeine and Class IV caramel in cola-type soft drinks and of caffeine, Class III caramel and riboflavin in energy drinks using synchronous fluorescence spectra. The synchronous fluorescence spectra were recorded at constant wavelength difference 90 nm from 200 to 500 nm. Reference values of analyte concentrations by high performance liquid chromatography (HPLC) with fluorescence detection combined with the standard addition method were used to create the partial least squares (PLS) models. High coefficients of determination (>0.99) were obtained in 0.2-4.2, 0.25-5.25, 0.4-10.0 and 0.007-0.054 mg L(-1) range for caffeine, Class III caramel, Class IV caramel and riboflavin, respectively. The PLS models were used to determine the concentration of analytes in different drink samples. The method provided comparable results with those found using the HPLC method.

Determination of methionine enantiomers by HPLC on the cyclofructan chiral stationary phase

The enantiomeric separation of methionine by high performance liquid chromatography on various cyclofructan type chiral stationary phases in the polar-organic separation mode was studied. The effects of the mobile phase composition and temperature on the enantioselectivity of the enantiomers were investigated. The enantioselective separation was attained on the isopropylcarbamate cyclofructan 6 chiral stationary phase with methanol/acetonitrile/acetic acid/triethylamine (75/25/0.3/0.2 v/v/v/v) as a mobile phase. The low retention and no separation were observed on the dimethylphenyl carbamate cyclofructan 7 and naphthylethyl carbamate cyclofructan 6 chiral stationary phases. Three types of detection, low-wavelength UV, polarimetric, and circular dichroism, were used. The UV detection limit for enantiomers was 11 μg mL−1 (S/N = 3) and the polarimetric and circular dichroism detection limits were 10 and 8 times lower. Good linearity was observed from 50 to 500 μg mL−1. The proposed method was applied to determine D- and L-methionine in a dietary supplement sample.

On-line coupling of molecularly imprinted solid phase extraction with liquid chromatography for the fast determination of coumarins from complex samples

Graphical abstract Figure. No Caption available. HighlightsThe on‐line MISPE‐HPLC method for selective determination of seven coumarins in various samples was developed.Developed and optimized method showed good validation results.Method was succesfully applied to analysis of Cassia cinnamon, chamomile tea and Tokaj specialty wines.Total time of whole analytical run, including extraction step was less than 13.50 min. Abstract In this work, an on‐line SPE‐HPLC method with spectrophotometric detection was developed for the determination of coumarins in complex samples. For the on‐line cleanup of samples, a molecularly imprinted polymer was packed into the column cartridge and coupled directly with HPLC (MISPE‐HPLC) using a column switching system. The separation of coumarins was performed on a C18 core‐shell column (100 × 4.6 mm, 5 &mgr;m) with a mobile phase consisting of 0.3% acetic acid/acetonitrile with gradient elution at a flow‐rate of 1 mL min−1. The total time of the whole analytical run, including the extraction step, was 13.25 min. The on‐line MISPE‐HPLC method was optimized and validated. The results showed good linearity (0.10–100 &mgr;g mL−1) with correlation coefficients higher than 0.99. The LOD values were from 0.03 to 0.15 &mgr;g mL−1. The proposed method was successfully applied for analysis of real samples (Cassia cinnamon, chamomile tea, and Tokaj specialty wines) and obtained recoveries varied from 78.7% to 112.2% with an RSD less than 9%.

Preparation and application of magnetic molecularly imprinted polymers for the selective extraction of coumarins from food and plant samples

In this study, magnetic molecularly imprinted polymers (MMIPs) were synthesized and characterized. Coumarin and 7-hydroxycoumarin were tested as templates for the preparation of MMIPs using the surface molecular imprinting technique on a magnetite (Fe3O4 nanoparticles) surface. Morphology, adsorption capacity, adsorption kinetics, and selectivity of the prepared MMIPs were investigated. From the abovementioned studies, it was found out that MMIP-7-hydroxycoumarin was capable to bind 80 μg of 7-hydroxycoumarin per g of polymer, showed relatively fast adsorption kinetics (30 min) and good selectivity towards target analogues. MIP-coumarin exhibited worse sorption, selectivity, and morphological properties. MMIP-7-hydroxycoumarin was applied for the selective extraction of coumarins from complex samples (food and plant). Coumarins were determined by HPLC with diode array detection. Precision, accuracy, and linear working range were determined under optimal experimental conditions. The developed methodology provided a limit of detection and quantification of 1.04 μg g−1 and 3.44 μg g−1 for coumarin and 1.76 μg g−1 and 5.92 μg g−1 for 7-hydroxycoumarin and 7-methoxycoumarin, respectively. The intra-day and inter-day repeatability of the method, in terms of the relative standard deviation, was less than 6.0% and 9.1%, respectively. The recovery values ranged from 71.4 to 90.3%.

Application of umbelliferone molecularly imprinted polymer in analysis of plant samples

The molecularly imprinted polymers (MIPs) were synthesised and the influence of the type of porogen, the nature of sample solvent, and the binding capacity of material were tested by high-performance liquid chromatography (HPLC). Umbelliferone was used as the template for imprint formation. Methacrylic acid was used as the monomer and acetonitrile, ethanol, and chloroform as porogen. Non-imprinted polymers (NIPs) were prepared by the same procedure. The highest value of the specific binding capacity (269 μg of umbelliferone per 100 mg of polymer) was obtained for polymers prepared in chloroform as porogen and methanol/water (φr = 1: 1) as the sample solvent. The group-selective MIP was used as sorbent for the SPE pre-treatment of umbelliferone from plant extracts prior to HPLC analysis. Analysis of the spiked samples showed good recoveries (> 77 %). The limit of detection, limit of determination, and repeatability of the method were also calculated.

In vitro study of enzymatic hydrolysis of diperodon enantiomers in blood serum by two-dimensional LC.

An on-line coupled HPLC system is described for the determination of the enantiomers of diperodon in blood serum. The method involves three steps: (i) off-line preconcentration and clean-up, (ii) separation of the diperodon enantiomers from the matrix components on a reversed-phase stationary phase, and (iii) separation of the racemate from the reversed-phase column on a teicoplanin chiral stationary phase. The method is suitable for simultaneous determination of both enantiomers in serum up to 0.5 microg/ml. The degradation of diperodon enantiomers was studied in serum by an in vitro method and the experimental rate constants were determined. The enantiomeric hydrolysis rates and half-lives for diperodon in serum are different.

Determination of Quinic and Shikimic Acids in Products Derived from Bees and their Preparates by HPLC

Abstract An HPLC method was developed for determination of some organic acids in propolis, honey, and pastilles. The on‐line coupled Separon SGX C18 and Polymer IEX H‐form column with mobile phase composed of sulphuric acid 9 mmol/L and methanol (95:5) at a flow rate 0.8 mL/min and spectrophotometric detection at 215 nm were used for the determination of quinic acid and shikimic acid. Limit of detection of quinic acid was 10 µg/mL and shikimic acid 0.43 µg/mL. Limits of quantitation were 30 µg/mL for quinic acid and 1.26 µg/mL for shikimic acid. Shikimic acid concentrations from 4.2 to 309.0 µg/g and quinic acid concentrations from 0.2 to 6.2 mg/g were determined in all tested bees products. The differences in the acid concentrations were observed for propolis samples from East and West Slovakia.

COMPARISON HPLC AND FLUORESCENCE SPECTROMETRY METHODS FOR DETERMINATION OF COUMARIN DERIVATIVES IN PROPOLIS

This paper illustrates the composition of propolis samples obtained from two regions in the Slovak Republic and focuses on the determination of coumarins. The HPLC method with on-line spectrophotometric and fluorescent detection was used for the separation and the determination of coumarins from the subgroup of simple coumarins (esculin, daphnetin, fraxetin, umbelliferone, 4-methylumbelliferone, 4-hydroxycoumarin, scoparone, coumarin, herniarin) and cinnamyl alcohol. The results confirmed that the quantity of umbelliferone, 4-methylumbelliferone, and scoparone in the propolis depends on the area of collection. The HPLC results were compared with those obtained by the spectrofluorimetric method developed for the determination of total coumarins (calculated as scoparone). For the quantification of total coumarins in propolis extracts we found 15% higher values of coumarin content by fluorescence spectrometry than by HPLC, which can be ascribed to the higher matrix effects on fluorescence spectra.

The Effect of Acetic and Formic Acid Formation during Accelerated Ageing on Embrittlement of Newsprint Paper

Paper and other lignocellulosic materials undergo deterioration as a result of ageing, influenced by various factors and accelerated by the formation of acids from components used in paper production and ambient species. These acids increase degradation of paper and decrease its mechanical properties. There is a lack of detailed information on the formation of acetic and formic acid in the process of accelerated ageing in the literature. This contributuion presents information on the kinetics of acetic and formic acid formation during accelerated ageing determined by modified ASTM D 6819-02 procedure. Accelerated ageing was performed with newsprint paper at 98°C and 50% RH for 60 days. The ratio of acetic acid to formic acid concentration increases through accelerated ageing by the factor after 10 days and by the factor 5.5 after 60 days. The brittleness index expressed as embrittlement due to paper degradation correlates well with the increase of the carboxylic acids concentration, as well as the molar ratio of concentration of acetic acid to formic acid. Zusammenfassung/résumé at end of article received: 04.04.2011 revised: 27.09.2011

Determination of Some Phenolic Acids in Propolis by an HPLC Method

Abstract The liquid chromatographic method was developed for determination of some organic acid in ethanol and water extracts of propolis from Slovakia. Analysis of chlorogenic acid, p‐hydroxybenzoic acid, and rosmarinic acid was realized with the chromatographic column Symmetry Shield RP18 type and using a gradient of mobile phase methanol‐water (pH=2.5 adjusted with formic acid) and spectrophotometric and fluorescence detection (for p‐hydroxybenzoic acid). Chlorogenic acid in the range from 2.7 to 56.6 µg/g and p‐hydroxybenzoic acid from 3.9 to 150.3 µg/g was determined in tested propolis samples. Rosmarinic acid concentration in all tested propolis samples was below the limit of detection in this method. The significant differences in the acids concentrations were observed for propolis samples from east and west of Slovakia. It is probably the effect of different conditions of the collection of the resin and secrets by bees.