Search results for "Concentration."
showing 10 items of 1849 documents
Interpretive search of optimal isocratic and gradient separations in micellar liquid chromatography in extended organic solvent domains
2020
Abstract Micellar liquid chromatography (MLC) is a reversed-phase mode with mobile phases containing an organic solvent and a micellised surfactant. Most procedures developed in MLC are implemented in the isocratic mode, since the general elution problem in chromatography is less troublesome. However, gradient elution may be still useful in MLC to analyse mixtures of compounds within a wide range of polarities, in shorter times. MLC using gradients is attractive to determine by direct injection moderate to low polar compounds in physiological samples. In these analyses, the use of initial micellar conditions (isocratic or gradient) with a fixed amount of surfactant above the critical micell…
Micellar Liquid Chromatography: A Worthy Technique for the Determination of β-Antagonists in Urine Samples
1998
Several beta-antagonists (acebutolol, atenolol, celiprolol, labetalol, metoprolol, nadolol, propranolol) were determined in urine samples with fluorometric detection after direct injection, in less than 15 min, with a micellar mobile phase of 0.1 M sodium dodecyl sulfate (SDS), 15% propanol, and 1% triethylamine at pH 3. The limits of detection (38 criterion) were usually between 3 and 30 ng/mL. The addition of propanol and triethylamine and the reduction of the pH of the mobile phase improved the efficiency of the chromatographic peaks that was rather low in pure micellar eluents. The selection of the composition of the mobile phase was easily performed through the use of an interpretive p…
Exposure assessment of fruits contaminated with pesticide residues from Valencia, 2001– 03
2006
A total of 634 samples of oranges, tangerines, peaches, nectarines, khakis and watermelons were collected from an Agricultural Valencia Community Cooperative during the May 2001 to April 2003 campaigns and they were analysed for 15 pesticides among those recommended for pest treatment. A conventional multiresidue analytical procedure based on ethyl acetate extraction was used followed by gas chromatography coupled to a nitrogen phosphorus detector for routine analysis; and mass spectrometry was performed for confirmation. Recovery studies with spiked samples at 0.5 mg kg-1 for each pesticide ranged from 52% for acephate to 87% for fenthion with a standard deviation20%. Limits of quantificat…
A new principle to normalize plasma concentrations allowing single-sample clearance determinations in both children and adults.
1992
A sufficiently accurate quantification of renal function requiring only one plasma sample without an additional gamma-camera study has, until now, only been possible in adults. A new principle will be presented here allowing the universal application of known algorithms, regardless of the clearance substance used, by normalizing the plasma concentrations with respect to the individual body dimensions of the patients - for infants as well as for adults. In this respect, algorithms are developed for clearance determinations using technetium-99m mercaptoacetyltriglycine (99mTc-MAG3), which are based on steady-state studies as the reference. They allow the calculation of quantitative clearance …
Effect of epidural anesthesia on colorectal anastomosis: a tonometric assessment.
1997
PURPOSE: Epidural anesthesia is believed to benefit colorectal anastomotic blood flow because of the sympathetic blockade it produces. Our purpose is to measure with tonometry the effect of epidural anesthesia on colorectal anastomotic oxygenation. PATIENTS AND METHODS: Fifteen patients operated on for rectal cancer (radical anterior resection) were monitored postoperatively using tonometers placed in the stomach (celiac trunk), transverse colon (superior mesenteric artery), and the anastomotic area during the operation. An epidural catheter was placed at L1-2, and on the first postoperative day, 8 ml of bupivacaine (0.25 percent) was administered. The anesthetic effect extended up to T-4. …
A New Evaluation of Emergency Methods for Artificial Ventilation
1968
SUMMARY The effect of artificial ventilation by the exhaled-air methods (mouth-to-nose and mouth-to-mouth) and chest-pressure-arm-lift methods (Ho-ward-Thomsen, Silvester-Brosch, Holger Nielsen) was investigated in 11 anaesthetised apnoeic volunteers. The efficiency of these methods was assessed by the changes in arterial PO2, O2 saturation, PCO2 and pH. It could be shown that the exhaled-air methods ensured normal PO2 and O2 saturation in all cases, while the ventilation by the manual methods was insufficient. Even though normal oxygenation was achieved by the manual methods in some cases, others were extremely hypoventilated, with critically low O2 tensions. pH and CO2 tensions did not ch…
Resting Energy expenditure in type 2 diabetic patients and the effect of insulin bolus
2014
Aims: Resting energy expenditure (REE) plays a critical role in the regulation of body weight, with important implications in type 2 diabetes (T2D). However, the relationships between REE and T2D have not been extensively evaluated. We compared REE in persons with diabetes and in persons without diabetes. We also investigated the acute effect of insulin on REE and venous lactate, the latter an indirect measure of neoglucogenetic activity. Methods: REE was measured using indirect calorimetry in 14 newly diagnosed, untreated T2D adults and in 14 non-diabetic age-, gender- and body mass index-matched persons. The REE and lactate venous concentrations were also measured in a subgroup of 5 T2D p…
Blood supply, oxygenation status and metabolic micromilieu of breast cancers: characterization and therapeutic relevance.
2000
The metabolic microenvironment of a tumor is predominantly determined by the efficacy of blood flow, flux parameters (such as diffusion and convective currents in the interstitial space) and metabolic rates. The most important factors in this context include oxygen and nutrient supply, tissue pH and the bioenergetic status. It is now widely accepted that the metabolic microenvironment of a tumor can dramatically influence a range of factors such as proliferation rate, cell cycle position, growth rate and the development of apoptosis and necrosis. At the same time, these parameters can have an impact on tumor detection, therapeutic response to conventional irradiation, some chemotherapy agen…
Cellular-free magnesium depletion in brain and muscle of normal and preeclamptic pregnancy: A nuclear magnetic resonance spectroscopic study
2004
Preeclampsia is a pregnancy disorder of unknown origin, characterized by vasospasm, elevated blood pressure, and increased neuromuscular irritability, features common to syndromes of magnesium deficiency. Evidence of serum and ionized magnesium metabolism disturbances have been observed in women with preeclampsia. This and the therapeutic utility of magnesium in preeclampsia led us to investigate the extent to which an endogenous tissue magnesium deficiency might be present in and contribute to its pathophysiology. We used 31 P nuclear magnetic resonance spectroscopy to noninvasively measure in situ intracellular-free magnesium levels in brain and skeletal muscle of fasting nonpregnant wom…
Liver disease in chelated transfusion-dependent thalassemics: the role of iron overload and chronic hepatitis C.
2008
Iron overload and hepatitis virus C infection cause liver fibrosis in thalassemics. In a monocentric retrospective analysis of liver disease in a cohort of 191 transfusion-dependent thalassemics, in 126 patients who had undergone liver biopsy (mean age 17.2 years; 58 hepatitis virus C-RNA positive and 68 hepatitis virus C-RNA negative) the liver iron concentration (median 2.4 mg/gr dry liver weight) was closely related to serum ferritin levels (R = 0.58; p<0.0001). Male gender (OR 4.12) and serum hepatitis virus C-RNA positivity (OR 11.04) were independent risk factors for advanced liver fibrosis. The majority of hepatitis virus C-RNA negative patients with low iron load did not develop liv…