Search results for "Photometry"
showing 10 items of 797 documents
Indirect spectrophotometric determination of p-aminobenzoic acid in sunscreen formulations by sequential injection analysis
2003
Abstract A simple indirect sequential injection spectrophotometric method for the determination of the UV-filter p -aminobenzoic acid (PABA) in sunscreen formulations is proposed. The determination is based on the reaction of PABA with hypochlorite in acidic medium and the subsequent measurement of the residual chlorine by using the well-known reaction with o -tolidine. The experimental variables involved in the sequential injection analysis (SIA) system (sandwich arrangement, volumes of sample and reagents, propulsion flow rate, reaction coil length) and adequate concentrations of reagents were studied. The SIA method has a linear range up to 20 μg ml −1 (3 s y / x / b detection limit) of …
Selective solid-phase extraction of organophosphorus pesticides and their oxon-derivatives from water samples using molecularly imprinted polymer fol…
2020
Abstract A molecularly imprinted polymer was synthesized and characterized to be used as solid-phase extraction sorbent for simultaneous chlorpyrifos and diazinon and their oxon derivatives. Several imprinted polymers were prepared and evaluated in a retention study of these analytes compared with a non-printed polymer. Several parameters affecting the extraction of imprinted polymer such as washing solvent, composition and volume of the eluting solvent and sample volume, were also investigated. Under the optimum conditions, the developed method provided satisfactory limits of detection ranging between 0.07 µg L−1 to 0.12 µg L−1 and the material showed an excellent reusability (> 50 reuses)…
Multi-pumping mechanised determination of selenium in natural waters by light emitting diode (LED) spectrometry
2009
It has been developed a fully mechanised procedure for the determination of selenium in waters employing a LED based spectrometer and solenoid multi-pumps as solution propelling devices. The proposed method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine, which oxidizes Variamine Blue to form a violet-colour species which absorb at 530 nm. The system was mechanised using the multicommutation process and a stopped flow strategy in the final step reaction. The analytical curve was linear between 0.010 and 0.500 mg L-1, with an equation ΔA = 0.501 (± 0.004) C and r = 0.999. The limit of detection (3σ/S) obtained for the proposed method was 0.00…
Determination of sulphonamides in human urine by azo dye precolumn derivatization and micellar liquid chromatography
1995
Abstract A high-performance liquid chromatographic method for the determination of sulphonamides in urine is reported. The drugs (sulphadiazine, sulphaguanidine, sulphamethizole, sulphamethoxazole, and sulphathiazole) were diazotized with nitrite and coupled with N-(1-naphthyl)ethylenediamine dihydrochloride in a sodium dodecyl sulphate (SDS) micellar medium. Separation of the sulphonamide azo dyes was performed on a C18 column with a 0.05 M SDS-2.4% pentanol mobile phase, which permitted the direct injection of the urine samples. The limits of detection were in the 0.1–0.3 μg/ml range.
Multicommutation as an environmentally friendly analytical tool in the hydride generation atomic fluorescence determination of tellurium in milk.
2003
The aim of this study is to show the advantages of the emerging multicommutation methodology based on the use of solenoid valves for Te determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS). The delivery of a series of alternating sequential insertions of small volumes of samples and reagents gives rise to new hydrodynamic processes and exciting analytical potentials by controlling the time of flow through the on/off-switched solenoid valves. This drastically reduces the reagent consumption by a factor of 4 and the generation of effluents (590 mL h(-1) instead of 750 mL h(-1) generated by the continuous-mode measurement) and also provides an improvement in th…
Comparison of different sorbents for on-line liquid-solid extraction followed by high-performance liquid chromatographic determination of nitrogen-co…
1998
Abstract LiChrolut EN [poly(styrene-divinylbenzene), PSDVB], Carbograph (graphitized carbon black, GCB), Isolute CN (cyanopropylsilica), Isolute C 2 (ethylsilica), and LiChrospher RP18 (octadecylsilica) were studied for on-line solid-phase extraction of twelve nitrogen containing pesticides from water. Determination (UV 210 nm) was performed with a Spherisorb C 8 analytical column and an acetonitrile-water gradient. The mean recoveries from 50 ml ranged from 83% for RP18 to 44% for GCB, and decreased in the following order: RP18, CN, LiChrolut EN, C 2 , and GCB. GCB showed poor recoveries due to incomplete desorption with the acetonitrile-water gradient used, and memory effects were detecte…
Resolution of overlapped non-absorbing and absorbing solutes using either an absorption null-balance detection window or multivariate deconvolution a…
2004
Abstract Non-absorbing alkyl ether sulfates (AES) can be separated using anthraquinone-2-carboxylic acid (AQCA) as a probe; however, absorbing alkyl benzene sulfonates (ABS), if present, interfere indirect detection of most AES oligomers. Overcoming of this interference, as well as the simultaneous characterisation and evaluation of AES, fatty acids and ABS, was accomplished by using a diode-array detector and the procedures here discussed. First, it was shown that ABS can be made undetectable by using a 9 nm wide and 227 nm centred charge-absorptivity null-balance detection window (NBDW), where its contribution to the absorbance cancels the dilution effects that its presence induces on the…
Flow-injection spectrophotometric determination of arylamines and sulphonamides by diazotization and coupling in a micellar medium
1991
Abstract In a sodium dodecyl sulphate (SDS) micellar solution, the rate of coupling of a diazonium ion with N-(1- naphthyl)ethylenediamine (NED) increases greatly, the protonation of the resulting azo dyes takes place at higher pH values and the dyes are more soluble. These favourable features were applied to the development of a simple flow-injection spectrophotometric procedure for the determination of diazotizable substances of pharmaceutical interest. Limits of detection in the range 0.2–0.5 μg ml−1 (signal-to-noise ratio=3), with relative standard deviation of 0.7–3% (n=3) for 5 μg ml−1 standards, were obtained.
Determination of sulfide in waters by flow-injection solid phase spectrophotometry
2000
A highly sensitive flow injection solid-phase spectrophotometric method was developed for the determination of sulfide in waters. The method is based on the formation of Methylene Blue (MB) by reaction between sulfide and N,N-dimethyl-p-phenylenediamine chloride in presence of Fe(III) in acidic medium. The MB formed was adsorbed on C18 bonded silica, located inside a laboratory-made flow cell, which was placed in the optical path of the spectrophotometer. Analyte retention and detection at 666 nm were performed simultaneously, followed by elution with a mixture of methanol and hydrochloric acid. Several variables of the system, such as amine concentration, acidity of the reaction medium, re…
Some observations on the automation by flow injection analysis of the spectrophotometric determination of amino acids and proteins witho-phthalaldehy…
1992
Automation by flow injection analysis with Spectrophotometric detection of the determination of total amino acids and proteins witho-phthalaldehyde is not straightforward. The use of spectrophotometry, instead of spectrofluorimetry, and of N-acetyl-L-cysteine, instead of the conventional mercaptoethanol is advantageous because of the lower variability of absorptivities with respect to fluorescence yields, and the larger stability of the derivatives. Under adequate working conditions and with leucine as reference, the procedure can be used for the evaluation of total amino acids. A similar procedure is proposed for the analysis of proteins in a sample. Limits of detection are ≈ 1 × 10−5M for…