Search results for " Limit"
showing 10 items of 1716 documents
Thermal lens spectrometric determination of cerium with oxine
1991
Abstract The spectrophotometric and photothermal (TLS) procedures for cerium determination using 8-hydroxyquinoline (oxine), after extraction into chloroform, are compared. Photothermal measurements are made using a coaxial pump/probe thermal lens spectrometer. The use of high-purity reagents at low concentrations permits a decrease in the TLS blank signal and noise, leading to a limit of detection of 9 × 10−9 M (cerium extract concentration), 40-fold lower than the spectrophotometric value. The dynamic range extended up to 6 × 10−7 M and the relative standard deviation for 5 × 10−7 M cerium was 3.9%.
Development and Optimization of Pre-Concentration Procedure of Rare-Earth Elements (REEs) in Their Minerals, Using Microwave - Assisted Sample Dissol…
2015
Abstract The aim of this research was to develop and optimize a procedure for determination of REEs in xenotime and monazite samples collected from Bangka Island, which were compared to Standard Monazite (71 AG) of Bureau of Analyzed Samples, London. ICP-OES method was used for the determination. The samples were dried and sterilized by heating for a week at 110 °C, before digesting with nitric acid and hydrofluoric acid, using a microwave-assisted digestion system. After a careful line selection, at the detection limits for all REEs in the ng/mL the REEs were reliably obtained at the 0.09 – 38% level.
Determination of NH(3) in pyrolysis gases by ammonia selective electrode.
1993
The suitability of ion-selective electrode for the determination of ammonia in pyrolysis gases of fossil fuels was studied. The ammonia was absorbed into acidic solution and two kinds of determination methods were carried out. The ammonia was either measured directly from the acid solution, or ammonia was first released into the gas phase and then determined (air gap method) by the ammonia selective electrode. The electrode functioned well in both cases, but the linear calibration range was rather narrow, slightly more than one tenfold. The quantitative detection limit in the water phase was 5 × 10−6M (0.085 ppm) NH3 and in gas phase operation solutions above 5 × 10−4M (8.5 ppm) NH3 it was …
A method for the determination of dimethylamine in air by collection on solid support sorbent with subsequent derivatization and spectrophotometric a…
2005
A new method for dimethylamine determination in air is reported. The proposed assay is based on the employment of C18-packed solid phase extraction cartridges for sampling. The retained amine is then derivatized inside the cartridges with the reagent 1,2-naphthoquinone-4-sulfonate. By observing the coloured area of the cartridge, a semiquantitative estimation of the amine can be made. It was also possible to distinguish between primary and secondary amines by visual inspection. Quantitative tests entailed desorption from the cartridges of the derivatives formed, and measurement of the absorbance of the collected extracts. The selected conditions were applied to quantify dimethylamine up to …
Sensitive determination of aliphatic amines in water by high-performance liquid chromatography with chemiluminescence detection.
2004
A sensitive method has been developed for liquid chromatographic determination of short aliphatic amines in water samples. Analytes are preconcentrated and dansylated on solid sorbents (C18 solid-phase extraction cartridges). The dansyl derivatives are chromatographed and post-column mixed with peroxyoxalate (TCPO) and H2O2 in order to perform chemiluminescence detection. Optimal results have been obtained using a sample volume of 5 ml. The method has been applied to the quantification or screening of several aliphatic amines: methylamine, ethylamine, butylamine, diethylamine, pentylamine and hexylamine. The screening procedure has been developed including also polyamines (putrescine, cadav…
Derivatization of amines in solid-phase extraction supports with 9-fluorenylmethyl chloroformate for liquid chromatography
1997
Abstract A new method based on reaction in solid-phase extraction cartridges with 9-fluorenylmethyl chloroformate is described for improved derivatization of amines prior to liquid chromatography. The effects of the reaction conditions, the kinetics of the reaction and the kind of packing material on the derivatization have been evaluated. The reliability of the described approach has been tested by derivatizing propylamine, diethylamine, diethanolamine, glycine, glutamic acid, p-aminobenzoic acid and β-phenylethylamine. Reaction yields compared with those of the analogous solution derivatizations were in the 44–169% range, and satisfactory linearity was achieved at concentrations of the am…
NUMERICAL-EXPERIMENTAL METHOD FOR THE ANALYSIS OF RESIDUAL STRESSES IN COLD-EXPANDED HOLES
2012
Hole cold expansion is a technique widely used to improve the fatigue life of components with holes, e.g. bolted or riveted joints. As it has been demonstrated in literature by analytical, numerical and experimental analyses carried out by several authors, the compressive residual stresses introduced by the hole cold expansion have a beneficial influence on both the static and the fatigue strength of the treated component, because they reduce significantly the typical stress peaks around the hole due to stress concentration. In the literature, various analyses of the residual stresses introduced by the hole cold expansion have been performed by using several methods such as X-ray diffractio…
Effective hydrostatic limits of pressure media for high‐pressure crystallographic studies
2007
The behavior of a number of commonly used pressure media, including nitrogen, argon, 2-propanol, a 4:1 methanol–ethanol mixture, glycerol and various grades of silicone oil, has been examined by measuring the X-ray diffraction maxima from quartz single crystals loaded in a diamond-anvil cell with each of these pressure media in turn. In all cases, the onset of non-hydrostatic stresses within the medium is detectable as the broadening of the rocking curves of X-ray diffraction peaks from the single crystals. The onset of broadening of the rocking curves of quartz is detected at ∼9.8 GPa in a 4:1 mixture of methanol and ethanol and at ∼4.2 GPa in 2-propanol, essentially at the same pressures …
Analytical prediction of ultimate moment and curvature of RC rectangular sections in compression
2013
This paper presents closed form expressions linking the ultimate bearing capacity to the ultimate curvature of rectangular RC sections subjected to axial load and bending moment acting in one of the two symmetry planes of the section. With respect to possible simplified formulations the following effects are also considered: confinement of the concrete, hardening of the longitudinal reinforcement, and presence of reinforcing bars distributed orthogonally to the neutral axis. The formulation is proposed in dimensional terms after a preliminary definition of the geometrical and mechanical parameters governing the structural response of the class of sections considered. The analytical expressi…