Search results for "mines"
showing 10 items of 2609 documents
o-Phthalaldehyde–N-acetylcysteine polyamine derivatives: formation and stability in solution and in C18 supports
2001
A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde-N-acetylcysteine (OPA-NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant (k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8 +/- 2 x 10(-2) min(-1) in solution versus 7.7 +/- 1.1 x 10(-4) min(-1) on the (C18) solid support. The results obtai…
Determination of tannic acid by direct chemiluminescence in a FIA assembly
2002
The determination of tannic acid is performed in a FIA assembly on the basis of the analytical output obtained by oxidation of the acid. The analyte solution was daily prepared in a mixture of quinine as sensitiser and perchloric acid and it was injected into a pure water stream acting as a carrier. This solution merges with the mixture potassium permanganate in perchloric medium and the resulting chemiluminescence is monitored. The method was applied over the range 0.5-20 mg l(-1) of tannic acid with a LOD 100 mug l(-1). The reproducibility was 2.1% and the sample throughput 54 h(-1). The influence of foreign substances was studied and the new method is applied to the determination of tann…
Determination of aliphatic amines in water by liquid chromatography using solid-phase extraction cartridges for preconcentration and derivatization
2001
Bond Elut C18 solid-phase extraction cartridges were used for preconcentration and pre-column derivatization with 3,5-dinitrobenzoyl chloride (DNB) of aliphatic amines in water. Conditions for analyte preconcentration and derivatization (including the volume of sample, concentration of reagent, time of reaction and pH) were investigated, using ethylamine, isopropylamine and dimethylamine as model compounds. On the basis of these studies, a rapid and sensitive method for the determination of aliphatic amines in water is presented. The analytes are retained and purified on the cartridges and then derivatized and desorbed by drawing in succession the DNB solution and acetonitrile. The collecte…
Determination of the Herbicide Fluometuron by Photo‐induced Chemiluminescence in a Continuous‐flow Multicommutation Assembly
2007
Abstract This study was dealing with the chemiluminometric determination of the selective herbicide Fluometuron or 1,1‐dimethyl‐3‐(α,α,α‐trifluoro‐m‐tolyl)urea, (C10H11F3N2O) with a molecular weight 232.29 belongs to the phenyl urea herbicides family. The analytical strategy is based on the continuous‐flow manifold, multicommutation and the analyte pre‐treatment, the photo‐degradation. The optimization of chemical (pH, medium, temperature, and organized media) and hydrodynamic parameters (volume of reagents and flow rate) was performed by univariant and multiparametric simplex procedure respectively. Analytical figures of merit and the effect of foreign substances were studied. The method r…
H-Point Curve Isolation Method for Coupled Liquid Chromatography and UV−Visible Spectrophotometry
2000
The H-point curve isolation method (HPCIM) for the detection of unknown interferences in chromatography is proposed. The method allows one to estimate the UV-vis spectra of interfering species in a sample as well as to test the purity of the chromatographic peaks. Besides the detection of the unknown interferences in a sample, this method allows one to calculate the concentration of an analyte in the presence of unknown compounds. To illustrate the reliability of the proposed method, samples of diuretics and amphetamines have been analyzed by normal- and reversed-phase high-performance chromatography.
Application of solid-phase microextraction combined with derivatization to the enantiomeric determination of amphetamines.
2005
Abstract The utility of combining chiral derivatization and solid-phase microextraction (SPME) for the enantiomeric analysis of primary amphetamines by liquid chromatography has been investigated. Different derivatization/extraction strategies have been evaluated and compared using the chiral reagent o -phthaldialdehyde (OPA)– N -acetyl- l -cysteine (NAC) and fibres with a Carbowax-templated resin coating. Amphetamine, norephedrine and 3,4-methylenedioxyamphetamine (MDA) were used as model compounds. On the basis of the results obtained, a new method is presented based on the derivatization of the analytes in solution followed by SPME of the OPA–NAC derivatives formed. The proposed conditio…
Determination of the herbicide benfuresate by its photo-induced chemiluminescence using flow multicommutation methodology.
2007
The present paper deals with an analytical strategy based on coupling photo-induced chemiluminescence in a multicommutation continuous-flow methodology for the determination of the herbicide benfuresate. The solenoid valve inserted as small segments of the analyte solution was sequentially alternated with segments of the NaOH solution for adjusting the medium for the photodegradation. Both flow rates (sample and medium) were adjusted to required time for photodegradation, 90 s; and then, the resulting solution was also sequentially inserted as segments alternated with segments of the oxidizing solution system, hexacyanoferrate (III) in alkaline medium. The calibration range from 1 microg L(…
Generalised H-point standard addition method for the isolation of the analyte signal from the sample signal when coelution of unknown compounds occur…
1999
The generalised H-point standard addition method (GHPSAM) is proposed for isolating the analytical signal of an analyte from the signal of an unknown sample. Samples containing two and three coeluting compounds have been analysed. The accuracy of the predictions depends on the shape of the analyte and interferent spectra but not on the degree of chromatographic overlap. This methodology involves the location of linear intervals for the unknown interference spectrum from the spectrum of the sample. Once the linear interval has been found the selection of three wavelengths within the interval will allow the cancellation of the signal of the unknown interferent. The method has been applied to …
“AND” luminescent “reactive” molecular logic gates: a gateway to multi-analyte bioimaging and biosensing
2014
This review outlines examples that illustrate a recent and highly innovative concept in the field of (bio)molecular sensing, namely the simultaneous multi-analyte detection using "reactive" luminescent probes that are able to produce an optical signal only in response to multiple (bio)chemical inputs and through covalent chemical reactions with target (bio)analytes. Unlike conventional "AND" molecular logic gates based on supramolecular photochemical mechanisms, these unusual "smart" optical (bio)probes are suitable tools to track the rise and fall of a wider range of biologically relevant analytes, in complex media and with higher selectivity. The potential utility of this concept for in v…
Two-Dimensional Indium Selenide for Sulphur Vapour Sensing Applications
2020
Surface-to-volume ratio in two-dimensional (2D) materials highlights among their characteristics as an inherent and intrinsic advantage taking into account their strong sensitivity to surface effects. For this reason, we have proposed in this work micromechanically exfoliated 2D nanosheets of InSe as an optical vapour sensor. As a proof of concept, we used 2-mercaptoethanol as the chemical analyte in vapour phase to monitor the change of the InSe photoluminescence (PL) before and after exposure to the analyte. For short vapour exposure times (at low analyte concentration), we found a PL enhancement of InSe nanosheets attributed to the surface localization of Se defects. For long vapour expo…