Frantisek Cacho

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 ultra trace concentrations of selenium using the GFAAS technique following on-line electrochemical pre-concentration on a gold-coated porous carbon electrode

In this work the possibility of determination of selenium in water samples was studied by on-line coupling of electrochemical pre-concentration flow through unit and GFAAS. The pre-concentration unit was created from a commercial electrochemical flow through analyser EcaFlow (Istran Ltd.) and a special two-electrode electrochemical flow through cell. The pre-concentration cell consisted of a working electrode made of gold-coated porous carbon and auxiliary electrode made of a Pt-wire. The pre-concentration unit was connected with electrothermal atomisers through 6-way valve with sampling loop. Using the proposed on-line coupling the limit of detection reached 0.01 μg L(-1) for a 10 mL sample. The total linear range was between 0.03 and 10 μg L(-1). From the number of ions tested only PO4(3-) ions reduced the signal by about 10% for 50-fold excess. Using this method it was possible to determine Se (IV) or the total inorganic selenium following reduction of Se (VI) by boiling the sample in HCl. The procedure was validated by analysing reference materials and a variety of water samples. A good agreement with the results of ICP-MS was achieved for all samples.

On-line electrochemical pre-concentration of arsenic on a gold coated porous carbon electrode for graphite furnace atomic absorption spectrometry

Trace arsenic was pre-concentrated from water samples in a two-electrode electrochemical flow cell coupled on-line to a graphite furnace atomic absorption spectrometer. The cell comprised a microporous electrode made of gold plated porous carbon material with a void volume of about 20 μL. The electrodeposition was performed from hydrochloric acid media, the deposit was stripped into diluted nitric acid and the pre-concentrate was transported to a loop of about 60 μL volume. The content of the loop was then transported by air flow to the graphite furnace and measured. Sample volumes up to 10 mL were pre-concentrated enabling to achieve detection limits down to 0.004 μg L−1. The procedure was validated by analyses of CRMs and various water samples. A good agreement with the hydride generation AAS was achieved for all samples.

Heavy metals determination using various in situ bismuth film modified carbon-based electrodes

Abstract The proposed work deals with the utilization of three carbon-based electrode substrates such as boron-doped diamond, glassy carbon and carbon paste for the preparation of in situ bismuth film modified electrodes. Such modified electrodes were subsequently used for the differential pulse anodic stripping voltammetric determination of heavy metal cations (Zn2+, Cd2+ and Pb2+) individually and simultaneously using similar experimental conditions (0.1 mol l−1 acetic buffer solution of pH 4.5 as supporting electrolyte with the addition of 0.1 mmol l−1 Bi3+, deposition potential of −1.4 V and deposition time of 120 s). The results showed that the modification step mostly enhanced the deposition and stripping process of studied cations when compared to the bare electrode substrates. A boron-doped diamond electrode was selected as the substrate for modification and the procedure was applied to the real sample analysis including water sample (certified reference material) and wastewater sample. Using the standard addition method the concentrations of particular heavy metals were quantified and the determined values were in a good agreement with those obtained by the reference method — high resolution atomic absorption spectroscopy with electrothermal atomisation and continual radiation source. This fact highlights that the developed in situ bismuth film modified boron-doped diamond electrode is a suitable electrochemical sensor to be applied to routine analysis of water samples containing heavy metals.

Sequential Determination of Total Arsenic and Cadmium in Concentrated Cadmium Sulphate Solutions by Flow-Through Stripping Chronopotentiometry after Online Cation Exchanger Separation

Flow-through stripping chronopotentiometry with a gold wire electrode was used for the determination of total arsenic and cadmium in cadmium sulphate solutions for cadmium production. The analysis is based on the online separation of arsenic as arsenate anion from cadmium cations by means of a cation exchanger. On measuring arsenate in the effluent, the trapped cadmium is eluted by sodium chloride solution and determined in a small segment of the effluent by making use of the same electrode. The elaborated protocol enables a full automatic measurement of both species in the same sample solution. The accuracy of the results was confirmed by atomic absorption spectrometry. The LOD and LOQ for Arsenic were found to be 0.9 μg dm−3 and 2.7 μg dm−3, respectively. A linear response range was observed in the concentration range of 1 to 300 μg dm−3 for sample volumes of 4 mL. The repeatability and reproducibility were found to be 2.9% and 5.2%, respectively. The linear response range for cadmium was found to be 0.5 to 60 g/L. The method was tested on samples from a cadmium production plant.

Atomic absorption spectrometry with electrothermal atomization to determine trace amounts of arsenic

Abstract The aim of this work was to develop an on-line coupling of electrochemical preconcentration to atomic absorption spectrometry method and to apply the developed system in the determination of ultra-trace amounts of As in water samples. A flow-through electrochemical analyzer EcaFlow (Istran Ltd, Bratislava, Slovakia) was used as the preconcentration unit with a two-electrode cell. The working electrode was a reticular vitreous carbon electrode coated with gold. An atomic absorption spectrometer SP9 with a graphite furnace atomizer (Pye Unicam) was used to determine the preconcentrated As species. Preconcentration parameters were optimized for the electrochemical process.