Vitamins, especially vitamin C, are important micronutrients found in fruits and vegetables. Vitamin C is also a major contributor to their antioxidant capacity. Lettuce is one of the most popular vegetables among consumers worldwide. An accurate protocol to measure vitamin C content in lettuce and other related species is crucial. We describe here a method using the ultra-high-performance liquid chromatography-ultraviolet (UPLC-UV) technique, in which sample preparation, vitamin extraction and chromatography conditions were optimized. Samples were collected to represent the entire plant, frozen at-80 °C and lyophilized to prevent undesirable oxidation and make their manipulation easier. The extraction of vitamin C was carried out in acidic media, which also contributed to its stability. As vitamin C can be present in two different interconvertible forms, ascorbic acid (AA) and dehydroascorbic acid (DHAA), both compounds should be measured for accurate quantification. The DHAA was quantified indirectly after its reduction to AA because AA shows a higher absorptivity than DHAA in the UV range of the spectrum. From the same extract, two measurements were carried out, one before and one after that reduction reaction. In the first case, we were quantifying the AA content, and in the second one, we quantified the sum of AA and DHAA (TAA: total ascorbic acid) in the form of AA. Then, DHAA quantity was indirectly obtained by subtracting AA coming from the first measurement from TAA. They were determined by UPLC-UV, using a commercial AA standard to build a calibration curve and optimizing the chromatographic procedure, to obtain AA peaks that were completely resolved in a short time. This protocol could
An experimental study of the clean-up before and after derivatization with BuMgCl in the determination of Me3Pb+, Et3Pb+ and Pb2+ in road dust is described. The analytical procedure consisted of an extraction at pH 9.0 (buffer) of the diethyldithiocarbamate complex in pentane followed by the evaporation to dryness and derivatization in hexane with BuMgC1. Me3BuPb, Et3BuPb and Bu4Pb are separated and quantified by gas chromatography-mass spectrometry in the selected ion monitoring mode. The adsorbents Florisil, Silicagel, alumina, Amberlite (XAD-2 and XAD-7) and Chromosorb with 3% and 10% deactivation degree were investigated for the clean-up. Prior to derivatization, Florisil, Silicagel and Alumina retained all the diethyldithiocarbamate complexes. The Amberlites (XAD-2 and XAD-7) and Chromosorb did not trap either diethyldithiocarbamate complexes or other interference compounds. After derivatization, alumina was to be the most effective adsorbent. Under these conditions, a recovery of 86.5% of Me3Pb+ was obtained using a road dust sample.
Nitrate is one of the most common groundwater contaminants in rural areas. In this work, the presence of high levels of nitrate in groundwater of the aquifers of the west part of Hoya de Huesca County (NE Spain) has been studied by coupling hydrogeological information with water sampling techniques through a wide areal sampling of 90 surface water and groundwater points belonging to several aquifers. The results showed a general hydrochemistry of calcium carbonate to calcium sulfate waters. Unlike other case studies in Mediterranean areas, in which nitrate pollution was associated with irrigated crops, the highest concentrations in the present study were found in dry farming areas in which winter cereal is grown. A monthly nitrate level monitoring, conducted in 21 selected points between 2016 and 2017, showed that the nitrate evolution pattern followed the N fertilizer application schedules in the sampling points in which the highest concentrations were recorded, whereas an annual regularity could be observed in the sampling points with low nitrate levels. The compilation of data for 16 selected points since 1990 shows that the problem is persistent and points to the need of implementing new aquifer pollution control measures, since the ones currently in force have not been successful.
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