Search results for " High pressure liquid"
showing 10 items of 705 documents
Ultrasound-Assisted Extraction, Centrifugation and Ultrafiltration: Multistage Process for Polyphenol Recovery from Purple Sweet Potatoes
2016
This work provides an evaluation of an ultrasound-assisted, combined extraction, centrifugation and ultrafiltration process for the optimal recovery of polyphenols. A purple sweet potato (PSP) extract has been obtained using ultrasonic circulating extraction equipment at a power of 840 W, a frequency of 59 kHz and using water as solvent. Extract ultrafiltration, using polyethersulfone (PES), was carried out for the recovery of polyphenol, protein and anthocyanin. Pre-treatment, via the centrifugation of purple sweet potato extract at 2500 rpm over 6 min, led to better polyphenol recovery, with satisfactory protein removal (reused for future purposes), than PSP extract filtration without cen…
An inter-laboratory validation of methods of lipid peroxidation measurement in UVA-treated human plasma samples
2010
Lipid peroxidation products like malondialdehyde, 4-hydroxynonenal and F2-isoprostanes are widely used as markers of oxidative stress in vitro and in vivo. This study reports the results of a multi-laboratory validation study by COST Action B35 to assess inter-laboratory and intra-laboratory variation in the measurement of lipid peroxidation. Human plasma samples were exposed to UVA irradiation at different doses (0, 15 J, 20 J), encoded and shipped to 15 laboratories, where analyses of malondialdehyde, 4-hydroxynonenal and isoprostanes were conducted. The results demonstrate a low within-day-variation and a good correlation of results observed on two different days. However, high coefficie…
Influence of photo-initiators in the preparation of methacrylate monoliths into poly(ethylene-co-tetrafluoroethylene) tubing for microbore HPLC.
2020
[EN] In this study, poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) polymeric monoliths were in situ developed within 0.75 mm i.d. poly(ethylene-co-tetrafluoroethylene) (ETFE) tubing by UV polymerization via three different free-radical initiators fscce-azobisisobutyronitrile (AIBN), 2,2-dimethoxy-2-phenylacetophenone (DMPA) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMPP). The influence of the nature of each photo-initiator and irradiation time on the morphological features of the polymer was investigated by scanning electron microscopy, and the chromatographic properties of the resulting microbore columns were evaluated using alkyl benzenes as test substances. The …
Pyrrolo[2,3-h]quinolinones: A new ring system with potent photoantiproliferative activity
2006
A new class of compounds, the pyrrolo[2,3-h]quinolin-2-ones, nitrogen isosters of the angular furocoumarin Angelicin, was synthesized with the aim of obtaining new photochemotherapeutic agents with increased antiproliferative activity and lower undesired toxic effects than the lead compound. Two synthetic pathways were approached to allow the isolation both of the dihydroderivatives 10-17 and of the aromatic ring system 23. Compounds 10-17 showed a remarkable phototoxicity and a great UVA dose dependence reaching IC(50) values at submicromolar level. Intracellular localization of these compounds has been evaluated by means of fluorescence microscopy using tetramethylrhodamine methyl ester a…
Retrospective analysis of pesticide metabolites in urine using liquid chromatography coupled to high-resolution mass spectrometry
2016
Abstract A comprehensive retrospective analysis of pesticide metabolites in urine was developed, using liquid chromatography coupled to Orbitrap high-resolution mass spectrometry (UHPLC-HRMS) that includes both post-run target (suspect screening) and non-target screening. An accurate-mass database comprising 263 pesticide metabolites was built and used for the post-run screening analysis. For non-target analysis, a “fragmentation-degradation” relationship strategy was selected. The proposed methodology was applied to 49 real urine samples from pregnant women. In the post-target analysis 26 pesticide metabolites were tentatively identified, 8 of which (2-diethylamino-6-methyl-pyrimidinol; 3-…
Study of the column efficiency using gradient elution based on Van Deemter plots.
2018
Performance of chromatographic columns is of major importance in the development of more efficient separation methods. So far, a common practice is to study the column behavior in isocratic elution by modifying the flow rate and fitting the theoretical plate height values versus the mobile phase linear velocity, according to the Van Deemter equation. In this work, an approach is presented to extend the measurement of efficiency to linear gradient elution, where the mean retention factor is kept constant at each assayed flow. This avoids a possible source of uncertainty due to the change in the distribution equilibria profile, and makes the mean interactions with the stationary phase in grad…
Association of vitamin D serum levels and its common genetic determinants, with severity of liver fibrosis in genotype 1 chronic hepatitis C patients.
2013
Background and aims: Lower 25-Hydroxyvitamin D (25[OH]D) serum lev- els have been associated with the severity of liver fibrosis in genotype 1 chronic hepatitis C patients (G1CHC). In addition, a recent genome-wide study identified genetic variants (rs12785878, near dehydrocholesterol reduc- tase, DHCR7; rs10741657, near CYP2R1; and rs7041, near vitamin D binding protein, GC) affecting 25(OH)D serum levels in healthy populations. We aimed to assess the association between vitamin D serum levels and its genetic determinants, with the severity of liver fibrosis. Material and methods: Two hundred sixty patients with biopsy-proven G1CHC were consecutively evaluated. The 25(OH)D serum levels wer…
Determination of ascorbic acid in plasma and urine by high performance liquid chromatography with ultraviolet detection.
1999
Abstract A reliable simple reversed-phase liquid chromatographic method for the routine determination of ascorbic acid in plasma and urine with ultraviolet detection is described. This method enables the complete separation of the ascorbic acid peak from others with a recovery of above 95 % within 8 minutes. The method can be used for analysing multiple samples within a day. In addition, the storage conditions and stability of ascorbic acid in plasma and urine were investigated. Samples of plasma and urine can be stored on ice in darkness for at least 60 min without reduction of ascorbic acid concentration. Prepared samples can be stored in darkness at 4 °C for at least 120 min and in liqui…
Vitamin A deficiency increases noise susceptibility in guinea pigs.
1990
The effect of vitamin A deficiency in guinea pigs on noise-induced temporary threshold shift (TTS) was evaluated after short (15 min) acoustic overstimulation with a moderate (90 dB) broad-band white noise. Some guinea pigs were fed ad libitum a purified diet deficient in vitamin A (VAD group) until biochemical signs of deficiency occurred. A second, control group (VA group) received the same diet as well as 100 IU vitamin A daily by pharyngeal tube. Cochlear potentials were recorded by special computerized equipment using implanted electrodes. Before acoustic stimulation, a baseline value was determined with a test stimulus [90 dBA (A-filter according to usual DIN instructions)] correspond…
Vitamin A in parenteral nutrition: uptake and distribution of retinyl esters after intravenous application.
1989
Short-term parenteral application of vitamin A was examined in rats. Retinyl margarinate, which is chemically similar to physiological retinyl esters, was used in vitamin A-depleted rats to study uptake, distribution, and storage of retinyl esters in tissues. Vitamin A-depleted and Vitamin A-sufficient rats were infused with a micellar suspension of retinyl margarinate for 7 h and then killed at different times. Retinyl margarinate was directly taken up by all tissues examined. It appears that infusion of retinyl esters in micellar form provides a direct way to supply vitamin A to peripheral, vitamin A-dependent tissues. Therefore, a short-term infusion of retinyl esters with an emulsifier …