Miriam E. Palomeque

Determination of phenol, resorcinol and hydroquinone in air samples by synchronous fluorescence using partial least-squares (PLS)

The determination of phenolic compounds is of great importance owing to their high toxicity. Some of them are present in tobacco smoke and it is important for their monitoring in air of closed room. A simple, rapid and sensitive method was developed for simultaneous determination of hydroquinone, resorcinol and phenol in this kind of samples. Synchronous fluorescence technique was used and the data were processed by using the partial least-squares (PLS) chemometric algorithm. The concentrations for experimental calibration matrix were varied between 0.02 and 0.2 mg L(-1) for hydroquinone, between 0.05 and 0.6 mg L(-1) for resorcinol and between 0.05 and 0.4 mg L(-1) for phenol in accordance with the national legislation. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method a recovery study on real samples was carried out.

Fluorimetric determination of fluoride in a flow assembly integrated on-line to an open/closed FIA system to remove interference by solid phase extraction

A simple flow injection fluorimetric method for fluoride determination is proposed. The method is based on the enhanced fluorescence of quercitin-Zr(IV) complex when fluoride ion is present in the sample. An open/closed FIA manifold with a mini-column of Dowex 50W X8 resin was used to remove the most important interference (aluminum). The two FIA assemblies were integrated on-line to automate the pretreatment of the water sample and fluoride determination. The calibration graph was linear over the range 0.1-3.0 mug ml(-1) of fluoride with a correlation coefficient of 0.999 and LOD 0.06 mug ml(-1). The relative standard deviation was 2.5% and the sample throughput was 52 h(-1) without pretreatment and 10 h(-1) with pretreatment of the sample. The method was applied to the determination of fluoride in water samples.

Flow injection biamperometric determination of captopril.

An automated method to determine captopril (1-[(2S)-3-mercapto-2-methylpropionyl]-L-proline) is proposed. A flow injection manifold based on the indirect biamperometric detection of the captopril by using Fe(III)/Fe(II) as an indicating redox system and a Z-shaped flow-cell configuration, was developed. The calibration curve is linear over the range 0.03-3.6 microg ml(-1) of captopril. The relative standard deviation for the determination of 0.76 microg ml(-1) of captopril is 0.97% (n = 12) and the sample throughput is 69 h(-1). This method was applied to the determination of captopril to commercially available pharmaceutical preparations.

New automatized method with amperometric detection for the determination of azithromycin.

A FIA-amperometric method for azithromycin determination was developed. A working glassy carbon electrode and a Ag/AgCl/NaCl (3M) reference electrode were used. The determination is based on the electrochemical oxidation of the azithromycin at 0.9V in Britton-Robinson buffer solution (pH 8.0). Due to the adsorption of the reaction products on the electrode surface, an effective cleaner cycle was implemented. By using the optimum chemical and FIA conditions, a concentration linear range of 1.0-10.0mgL(-1) and a detection limit (LOD) of 0.76mgL(-1) are obtained. The method was validated and satisfactorily applied to the determination of azithromycin in pharmaceutical formulations.

Flow-injection fluorimetric determination of mercury(II) with calcein

A flow-injection spectrofluorimetric method for the determination of Hg(II) is described. The method is based on the complex that is formed between Hg(II) and calcein at pH 11-12. This reagent was not used before for determining Hg(II). The excitation wavelength is 324 nm and the emission wavelength is 522 nm. The calibration graph shows a linear range between 7.7 and 128 microg l(-1) (relative standard deviation 2.0%), the sampling rate was 90 h(-1). The effect of several interferents has been examined. Trace mercury in natural waters were determined satisfactorily using a modified manifold, which has an EDTA stream in order to minimize the calcium and magnesium interference.

Determination of V(V) by a kinetic stopped-flow FIA method with spectrophotometric detection

In the present paper, two automatised methods to determine V(V) in water samples are described. A continuous flow system based on the classical reaction for the determination of vanadium(V) with 3,3 0 dimethylnaphtidine in acid medium, by using a stopped-flow technique and spectrophotometric detection was developed (Method A). It was possible to increase the kinetic of the reaction obtaining a higher sample throughput (34 h ˇ1 ), lower detection limits (0.2 mg l ˇ1 ) and a high sensitivity. In order to determine still a lower concentration levels of V(V), a preconcentration step has been introduced in the above system (Method B). This manifold has a lower detection limits (0.032 m gm l ˇ 1 ) and a high sensitivity (4 times greater than Method A). Both methods show a good reproducibility (RSD: Method Aa1.9% and Method Ba2.3%). # 1998 Elsevier Science B.V.

Enzymatic reverse FIA method for total phenols determination in urine samples

A reverse flow injection spectrophotometric enzymatic method is proposed to quantify total phenols in urine samples. The polyphenol oxidase (PPO; EC 1.14.18.1) obtained as a crude extract from sweet potato root (Ipomoea batatas) was used as enzymatic catalyze. The detection limit, the sample throughput and relative standard deviation were 7.7mgl(-1) of total phenols, 49h(-1) and 0.9%, respectively. The method was applied to real samples and a recovery study was carried out in order to its validation.

AUTOMATED FLOW-INJECTION METHOD FOR CADMIUM DETERMINATION WITH PRE- CONCENTRATION AND REAGENT PREPARATION ON-LINE

The spectrophotometric determination of Cd(II) using a flow injection system provided with a solid-phase reactor for cadmium preconcentration and on-line reagent preparation, is described. It is based on the formation of a dithizone-Cd complex in basic medium. The calibration curve is linear between 6 and 300 µg L-1 Cd(II), with a detection limit of 5.4 µg L-1, an RSD of 3.7% (10 replicates in duplicate) and a sample frequency of 11.4 h-1. The proposed method was satisfactorily applied to the determination of Cd(II) in surface, well and drinking waters.

Studies on styrene phosphonic acid

Some properties of styrene phosphonic acid (SPA) were studied. The crystals were triclinic, witha=0.6434 nm,b=0.5842 nm,c=2.0338 nm, α=96.17°, β=97.33°, γ=79.65° andZ=4. SPA underwent a change in crystal structure at 78.8°C, the hydrocarbon network became disordered (“liquid-like”) at 138.5°C. Crystals melted at 148.6°C giving a cubic mesophase, then changed to an isotropic liquid at 155.6°C and at 162.13°C SPA underwent decomposition. Values for pK1=2.15 and pK2=7.66 were obtained at 25°C. The water solubility of SPA at several temperatures, and its interaction with surfactant micelles were determined.

Vanadium(V)-alizarine red-cetyltrimethylammonium bromide interaction and its implications in molecular absorption spectrometry

Abstract The structure of the vanadium (V)-alizarine red-cetyltrimethylammonium complex and its location in cetyltrimethylammonium bromide micelles were studied to elucidate the conditions required to obtain an absorption bathochromic shift and enhanced absorption in the UV-VIS spectrum when a surfactant is added to a metal complex. It was found that the chromogenic ligand must have quinone groups and its structure must allow these groups to be located in the micelle electrical double layer and also allow both electrostatic and hydrophobic bonding with the cationic surfactant.