Search results for "Sodium hydroxide"
showing 10 items of 42 documents
Consolidation of earthen building materials: a comparative study
2019
The consolidation and protection of mud bricks are a challenge in the field of conservation of archeological sites. One of the solutions is represented by the coverage of the entire excavation that assures a protection against mud dissolution. Unfortunately, this is not always feasible, both for economical and practical issues. For these reasons, alternative solutions are needed. In this work, laboratory experimentation has been carried out in order to test the efficacy of some products to slow down the dissolution process and increase the brick toughness. Three typologies of raw materials taken from different outcrops (one from the Republic of Azerbaijan and two from Calabria region, Italy…
Detection of gamma-hydroxybutyrate in hair: Validation of GC–MS and LC–MS/MS methods and application to a real case
2012
A gas chromatography-mass spectrometry (GC-MS) and a liquid chromatography tandem mass spectrometry (LC-MS/MS) method were validated for quantifying endogenous and exogenous hair concentrations of gamma-hydroxybutyrate (GHB). The GC-MS method is based on overnight extraction of 25 mg hair in NaOH at 56 °C, liquid/liquid extraction in ethylacetate and trimethylsylil derivatization; analysis is by electron ionization and single ion monitoring of three ions. The LC-MS/MS method entails a rapid digestion of 25 mg hair with NaOH at 75 °C for 40 min, liquid/liquid extraction in ethylacetate and reconstitution of the extract in the LC mobile phase; negative ion electrospray ionization and multiple…
Determination of low-molecular-mass aliphatic carboxylic acids and inorganic anions from kraft black liquors by ion chromatography.
2007
An ion chromatographic (IC) method with suppressed conductivity detection (CD) was developed and validated for the quantitative determination of several low-molecular-mass aliphatic mono- and dicarboxylic acids as their carboxylate anions together with some inorganic anions (chloride, sulfate, and thiosulfate) from kraft black liquors. To confirm the identification of some carboxylate anions which lack commercial model substances, a qualitative IC method with suppressed electrospray ionization mass spectrometry (ESI-MS) was also developed. The separations were performed on an IonPac AS 11-HC anion-exchange column operated at 25 degrees C within 25 min by a gradient elution with aqueous pota…
Synthesis of phenol–formaldehyde resole resins in the presence of tetraalkylammonium hydroxides as catalysts
2000
Abstract We synthesised phenol–formaldehyde resole resins in the presence of tetraalkylammonium hydroxides as catalysts. The activity of these catalysts was compared with the activity of sodium hydroxide. Gas chromatography, thin layer chromatography, 13 C NMR spectrometry, potentiometric titration and a few simple physicochemical methods were used to estimate the composition of the obtained resins and their properties. It was concluded from these studies that tetraalkylammonium hydroxides are active catalysts and the resins obtained in their presence show some interesting properties.
Multi-elemental determination of heavy elements in plastics using X-ray fluorescence after destruction of the polymer by molten sodium hydroxide
1992
In this paper a method is proposed for the multielemental analysis of Sb(III), Ba, Cd, Cr(III), Hg, Pb and As(III) in plastics, using X-ray fluorescence after alkaline decomposition and preconcentration by (co)precipitation. The organic matrix is destroyed by decomposition with sodium hydroxide melted in a silver crucible by the open system technique, using sodium nitrate as auxiliary oxidant. The variables which influence preconcentration are optimized: digestion time, pH, salinity, carrier and sodium diethyldithiocarbamate (DDTC) and sodium rhodizonate (R) as precipitants. The calibration curves were linear up to 200 μg of the element present, except for lead (150 μg) antimony(III) (100 μ…
Assessment of Postharvest Dehydration Kinetics and Skin Mechanical Properties of “Muscat of Alexandria” Grapes by Response Surface Methodology
2016
The dipping of berries in a dilute solution of sodium hydroxide during a short time was evaluated as pretreatment undertaken prior to convective dehydration of wine grapes. The impact of the sodium hydroxide content and dipping time on weight loss (WL) at different dehydration times was thoroughly assessed using central composite design (CCD) and response surface methodology (RSM). Furthermore, the effects of these two variables were also investigated on the skin mechanical properties of dehydrated grapes. The effect of these two pretreatment factors on the dehydration kinetics and skin hardness was satisfactorily fitted to regression models. The berry pretreatment with low sodium hydroxide…
Spectrophotometric determination of fluoride in fluoride-bearing minerals after decomposition by fusion with sodium hydroxide
1984
The decomposition of highly insoluble minerals (fluorspar and cryolite) by fusion with molten alkali-metal hydroxides is studied. The introduction of additives such as aluminium compounds or sodium peroxide to obtain total liberation of fluoride from calcium fluoride samples, is tested. The fusion is done in a silver crucible with a Bunsen burner. The cooled melt is easily soluble, giving solutions suitable for spectrophotometric fluoride determination by the Zr(IV)-fluoride-Erichrome Cyanine R method.
Removal of trivalent chromium from tannery waste waters using bone charcoal
2002
International audience; The ability of bone charcoal to remove Cr(III) from aqueous solutions by adsorption has been investigated. The adsorbent used was first characterised and then the adsorption was studied as a function of time and amount of charcoal. Tests were carried out with synthetic solutions whose Cr concentrations (500 mg L-1) were similar to those found in some effluents of Moroccan tannery industries. Cr removal efficiencies higher than 90% were obtained at pH 3.5 using 3 g of bone charcoal and a stirring time of about 30 min. Results of Cr removal by all sieved fractions of bone charcoal had shown the same interesting capabilities for Cr(III) retention. The cross interference…
Properties of trialkylamines as catalysts of resoles synthesis
2000
A series of the syntheses of phenol–formaldehyde resoles was carried out in the presence of trimethyl-, triethyl-, tripropyl-, and tributylamines and sodium hydroxide as catalysts for this process. The rate constants were calculated for the partial reactions identified in the synthesis. Also, the performance properties of the resins obtained and the hardened resin samples were estimated in simple tests. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 898–902, 2000
Atomic-absorption spectrometric determination of calcium, magnesium and potassium in leaf samples after decomposition with molten sodium hydroxide
1991
Abstract The decomposition of standard leaf samples of varied origin and nature by fusion with sodium hydroxide in an open system has been studied. The use of sodium nitrate as an auxiliary agent facilitated the mineralization of most of the samples. The solutions obtained were analysed for calcium, magnesium and potassium by flame atomic-absorption spectrometry. The method is fast and quite precise, with absolute standard deviations of 0.04–0.13, 0.002-0.03 and 0.04–0.12% for calcium, magnesium and potassium contents of O.8-5.0, 0.13–0.48 and 0.36–2.2% respectively. The limits of detection (μg/ml) in the determination step were 0.10 for calcium, 0.011 for magnesium, and 0.09 for potassium.