RESUMEN
The novel, automated, multi-pumping flow system (MPFS) for online calibration and determination of nitrate in surface water is presented for the first time. The system was equipped with micropumps of three different nominal volumes (10, 20, and 50 µL). As a result, it was possible to prepare from one standard, directly in a flow system, up to seven standard solutions. Determination of nitrate was conducted in stop-flow conditions and is based on a commercially available ion selective electrode (ISE) application. It was found that the linearity and slope of the calibration graphs depend mainly on the characteristics of the ISE. The obtained results were very repeatable, owing to the high precision of the micro-pumps used. The R.S.D. for the stroke volume of each micro-pump was below 1%. The accuracy of the method was checked through determination of nitrate in surface water samples. The obtained results were compared with those of the reference method (photometric Hach cuvette tests). It was found that, at a 96% confidence level, the difference between the results obtained by the proposed method and the reference method was statistically insignificant. The accuracy of the method was confirmed through the determination of nitrate in Certified Reference Material. The relative deviation (R.D.) of the measured and the certified concentrations was 5%.
RESUMEN
BACKGROUND: In line with the current tendency towards the production of the so-called safe foods, the use of environmentally-friendly methods for the extraction of polyphenols from fruits has been sought. Citric acid is a good solvent in the preparation of phenolic compounds for the food and pharmaceutical industries because it is a natural antioxidant and is non-toxic for the environment. Furthermore, new sources of polyphenols from fruit of orchard plants that are less known in Poland have been looked for. The aim of this study was to assess the content and antiradical activity of polyphenolic compounds in fruit extracts, depending on the extraction method employed. In addition, the yield of extraction processes was assessed. METHODS: The experimental materials were fruits of the following plants: Actinidia arguta, Crataegus monogyna, Gaultheria procumbens, Schisandra chinensis. For the extraction, aqueous solutions of citric acid (CAE) and methanol (ME) were used. The following were determined in fruit extracts: the content of total phenols (TP) and anthocyanins (A), and antiradical activity (DPPH and ABTS). RESULTS: In general, the C. monogyna fruit extracts were distinguished by the highest TP and A content. The TP and A content was significantly higher in fruit extracts obtained with the CAE method than in the ones produced with the ME method. The highest mean A/TP ratio was determined for S. chinensis fruit extracts. The antiradical activity (DPPH and ABTS) in fruit extracts did not depend on an extraction method, but on fruit species. Overall, a higher yield of extraction processes was achieved for the CAE method than for the ME method. CONCLUSIONS: The present study indicates that the selected extraction methods are able to obtain polyphenolic extracts from fruits with a high antiradical activity and high yield. The use of citric acid in order to extract polyphenols from fruits may be an alternative to the conventional extraction method, while being eco-friendly and more effective than the latter.