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A polystyrene divinyl benzene (8%) copolymer has been functionalized by coupling it through N N group with 2-naphthol-3,6-disulfonic acid (NDSA). The resulting resin has been characterized by elemental analysis, thermogravimetric analysis and infrared spectra. The hydrogen ion, water regain and metal ion capacities of the resin have been determined. Two forms of chromium show different exchange...
Lead concentration in lake sediment samples has been determined by means of ultrasonic slurry sampling electrothermal atomic absorption spectrometry USSS-ETAAS. The soil samples were suspended (0.025-0.15% w/v slurry) in four different liquid media containing 0.5% (v/v) nitric acid, 5% (v/v) nitric acid, 0.5% nitric acid+Triton X-100 and 5% nitric acid+Triton X-100. The effects of the instrumental...
Robustness experiments are performed in analytical chemistry to assess the behaviour of an analytical procedure under conditions slightly different from those of the experimental optimum. This work presents a study of robustness applied to a previously proposed fluorescent methodology using two replicated 2 7-4 saturated fractional factorial designs. A comparison is established between...
An off-line optimization technique based on soft modeling methods has been used to determine the optimum conditions for the separation of eight carbonyl-2,4-dinitrophenylhydrazones by gas chromatography equipped with a nitrogen-phosphorous detector. In this method theoretical simulations of peak retention time and peak width at base-line are coupled to a factorial design to map the chromatographic...
The use of multilayer perceptrons (MLP) feedforward neural networks trained by back-propagation (BP) for non-linear QSAR model building is presented and explained in detail through a case study. This method was compared with others often used in this field, such as multiple linear regression (MLR), partial least squares (PLS) and quadratic PLS (QPLS). The case study deals with a series of 18 alpha...
The electrochemical response of metal ions in different samples of coloured ceramic tin-lead glazes attached to graphite/polyester composite electrodes is described. In addition to the ubiquous signals for lead, reductive dissolution processes are followed by anodic stripping peaks for Co, Cu, Sb, Mn, Sn and Fe, enabling the direct identification of such elements in microsamples proceeding from archaeological...
Obtaining completely uniform distribution of the active principle and excipients in a pharmaceutical preparation is essential with a view to ensuring correct dosage. Uniformity in pharmaceutical formulations has usually been controlled by collecting samples at different stages of the process in order to determine the active principle using a chromatographic or UV-Visible spectroscopic method. In this...
The need for highly reliable methods for the determination of trace elements has been recognised in analytical chemistry and environmental science. A method for the trace analysis of Pb and Cd in natural waters is described. In a preconcentration step, 500 ml of an aqueous sample containing lead and cadmium were extracted into 3.5 ml of a solution containing a complexing agent (dithizone) in xylene...
The utility of carbon paste electrode modified with DTPT (3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine thione) for the potentiometric determination of Cu(II) in aqueous medium is demonstrated. The electrode exhibits linear response to Cu(II) over a wide concentration range (9.77x10 -7 -7.6x10 -2 ) with Nernstian slope of 30+/-2 mV per decade. It has a response time of about...
A sensitive method for the quantitative determination of acrivastine was developed based on the reduction of the drug at the dropping mercury electrode. A well-developed polarographic wave was produced in Britton-Robinson buffers over the pH range 0.0-11. The overall reduction process was diffusion-controlled with limited adsorption properties. At pH 5, the diffusion-current constant (I d ...
In this study, the feasibility of using the in vitro absorption spectra of phytoplankton samples, for determining the relative abundance of specific classes of the phytoplankton, was investigated. Single species cultures of nine algae, representing six phytoplankton classes, were used. Mixtures of algal cultures were also prepared for analysis. In total, 25 samples were examined. Spectra were recorded...
A new kinetic spectrophotometric method for the determination of oxalate has been described, based on its enhancing effect on the oxidation of Mn(II) to MnO 4- , which is measured at 525 nm, by potassium periodate. Under the optimum conditions of 20 μgml -1 Mn(II) in MnSO 4 .H 2 O/0.015 moll -1 H 3 PO 4 /0.013 moll -1...
Azorubin (E 122), Ponceau 4R (E 124) and Allura red (E 129), are the most used red dyes in soft drinks manufacturing, and in some cases two dyes are present. The aim of this work is to show that using differential pulse polarography, it was possible to distinguish these synthetic dyes from the natural dyes providing from fruits. In addition, in an appropriate supporting electrolyte, identification...
In this work, we present the results obtained in an analytical study of the different types of proteinaceous binding media most commonly used in paintings, using GC-FID as the technique of analysis and GC-MS as a confirmatory technique. The application of this methodology requires prior hydrolysis of the proteins in the binding media to obtain free amino acids and then volatile derivatives, in this...
The determination of trace metals in solid samples has traditionally been performed by acid digestion and subsequent measurement by a suitable instrumental technique. This dissolution step is time-consuming and it shows important drawbacks. For these reasons, in the past years many efforts have been focused on the direct analysis of solid samples. Among the developed methodologies, slurry sampling-electrothermal...
A simultaneous and fast method for the determination of total polyphenol index (t.p.i.) and total anthocyan index (t.a.i.) has been developed by a flow injection approach and a diode array spectrophotometer for monitoring at 280 and 520 nm, respectively. Linear ranges were obtained from 20 to 70 index units and from 20 to 500 mg l -1 for the t.p.i. and t.a.i., respectively. The results...
A flow injection method on the basis of gas phase molecular absorption is described for the determination of nitrite in the aqueous solution. 200 μl of nitrite solution is introduced into a carrier stream of distilled water. The carrier stream containing nitrite zone is reacted with a stream of hydrochloric acid (2 M). The stream is then segmented by O 2 gas. The produced gaseous products...
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