Search results for "buffer"
showing 10 items of 230 documents
Dependence of plasma pH on oxygen saturation
1969
Abstract The influence of haemoglobin oxygenation on the pH value of the blood plasma of healthy adolescents was investigated at 38°C by varying the parameters CO2 pressure, Hb concentration and buffer bases. A total of 5000 measurements gave the following results: 1. 1. The pHs difference between oxygenated and deoxygenated blood increases with diminishing CO2 pressure and with increasing Hb concentration. There is a linear relation between the pHs changes and the O2 saturation of the haemoglobin. 2. 2. Quantitatively these relationships can be expressed by the following equation: δpHs = (8 − pH ox − log 0.03 Pco 2 ) · [Hb] 225 · (100 − So 2 100 where ΔpHs is the pHs difference between par…
Determination of ethyl sulfate – a marker for recent ethanol consumption – in human urine by CE with indirect UV detection
2006
A CE method for the determination of the ethanol consumption marker ethyl sulfate (EtS) in human urine was developed. Analysis was performed in negative polarity mode with a background electrolyte composed of 15 mM maleic acid, 1 mM phthalic acid, and 0.05 mM cetyltrimethylammonium bromide (CTAB) at pH 2.5 and indirect UV detection at 220 nm (300 nm reference wavelength). This buffer system provided selective separation conditions for EtS and vinylsulfonic acid, employed as internal standard, from urine matrix components. Sample pretreatment of urine was minimized to a 1:5 dilution with water. The optimized CE method was validated in the range of 5-700 mg/L using seven lots of urine. Intra-…
Integration of cognitive allocentric information in visuospatial short-term memory through the hippocampus
2005
Visuospatial short-term memory relies on a widely distributed neocortical network: some areas support the encoding process of the visually acquired spatial information, whereas other ares are more involved in the active maintenance of the encoded information. Recently, in a pointing to remembered targets task, it has been shown in healthy subjects that, for memory delays of 5 s, spatial errors are affected also by cognitive allocentric information, i.e., covert spatial information derived from a pure mental representation. We tested the effect of a lesion of the hippocampus on the accuracy of pointing movements toward remembered targets, with memory delays falling in the 0.5-30 s range. The…
Unstimulated salivary flow rate, pH and buffer capacity of saliva in healthy volunteers
2004
Objectives: To assess the salivary flow rate, pH, and buffer capacity of healthy volunteers, and their relationships with age, gender, obesity, smoking, and alcohol consumption, and to establish the lower-end value of normal salivary flow (oligosialia). Methods: A prospective study was conducted in 159 healthy volunteers (age > 18 years, absence of medical conditions that could decrease salivary flow). Unstimulated whole saliva was collected during ten minutes, and salivary flow rate (ml/min), pH, and bicarbonate concentration (mmol/l) were measured using a Radiometer ABL 520. The 5 percentile of salivary flow rate and bicarbonate concentration was considered the lower limit of normality. R…
The unpleasantness of tonic pain is encoded by the insular cortex
2005
Objective: Muscle pain differs from skin pain with respect to quality, accuracy of localization, and unpleasantness. This study was conducted to identify the brain regions associated with the affective-motivational component of tonic skin and muscle pain. Methods: Forty healthy volunteers were investigated in three groups with different F-18 fluorodeoxyglucose PET activation scans. A verbal rating scale (VRS) was used to quantify pain intensity and unpleasantness. One group was investigated during painful infusion of an acidified phosphate buffer (pH 5.2) into either muscle or skin for 30 minutes. Muscle and skin infusions were adjusted to achieve pain intensity rating of VRS = 40. The seco…
Beyond Biodegradability of Poly(lactic acid): Physical and Chemical Stability in Humid Environments
2017
International audience; Poly(lactic acid) (PLA) is the most traded biodegradable and biobased material. It is largely used as ecofriendly substitute of conventional plastics. Nevertheless, one of the main limiting factors is its water sensitivity. PLA reacts with water and is hydrolyzed during time, which determines its performance. Limited information related to the hydrolysis mechanism driven by water in vapor state is available in scientific literature. Literature is mainly focused on the effects of water in liquid state. This lack of information is of significant importance, since PLA interacts with water in both phases. This work was aimed to give a full depiction of the chemical and p…
Selective determination of trimethylamine in air by liquid chromatography using solid phase extraction cartridges for sampling.
2004
Abstract The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn ( 20 mm ×2.1 mm i.d., packed with 30 μm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column ( 125 mm ×4 mm i.d., LiChrospher 100 RP18, 5 μm), and monitored at 262 nm. The method was applied to …
Characterization of poly(4-vinylpyridine 1-oxide) by free-solution capillary electrophoresis and micellar electrokinetic chromatography
2008
The migration characteristics of poly(4-vinylpyridine 1-oxide) (PVP-NO) in phosphate buffers of acidic pH (20 mM H 3 PO 4 or NaH 2 PO 4 ) have been studied using both free-solution capillary electrophoresis (FSCE) and MEKC. To inhibit adsorption, 250 mM o-phosphoethanolamine (2-aminoethyl dihydrogen phosphate) was used. In FSCE, PVP-NO showed a narrow peak and a broader band, both having anionic behavior. These peak and band were attributed to the free and aggregated or micellized PVP-NO forms, respectively. According to surface tension measurements, the CMC of SDS in the BGE was 1.8 and 0.48 mM in the absence and in the presence of 1000 μpg/mL PVP-NO, respectively, and the association of t…
In situ AFM study of proton-assisted electrochemical oxidation/reduction of microparticles of organic dyes
2008
In situ atomic force microscopy (AFM) images of crystals of organic dyes alizarin, indigo and morin have been monitored during the course of their solid-state electrochemical oxidation/reduction in contact with aqueous acetate buffer. Such images indicate that proton-assisted reduction and oxidation processes are localized in a shallow layer in the vicinity of the particle/electrolyte interface, in agreement with expectances from the Lovric and Scholz model with significantly restricted proton diffusion across the solids. Keywords: Voltammetry of nanoparticles, Atomic force microscopy, Organic dyes, Diffusion
Prospects of Ion Chemical Reactions with Heavy Elements in the Gas Phase
2001
Heavy element chemistry is related to the fundamental interest that lies in exploring the upper limits of the periodic table. Chemical properties of the heaviest elements have already been studied at single atoms in aqueous solutions and in the gas phase up to an atomic number Z = 107. These techniques allow to study nuclides with half lives as short as about 1 s. Next generation chemistry experiments could be envisaged with an ion trap technique already developed for stable isotopes. At very low production rates in the order of 1 per 100 s and/or half lives as short as about 10 ms, the ion-molecule reactions can be studied in a buffer gas cell, in which the heavy elements are stopped and t…