F. Alés Barrero

ALAMIN: a chemometric program to check analytical method performance and to assess the trueness by standard addition methodology

Abstract ALAMIN is a DOS program that establishes the performance characteristics of the analytical method from the calibration data set. It allows an estimation of the maximum level of interferents that causes a bias equal to or greater than the random error of determination. A statistical protocol checks the trueness of the analytical method by standard addition methodology. This shareware program is available from the authors upon request.

Sequential response surface methodology for multioptimization in analytical chemistry with three-variable Doehlert designs

Abstract In this paper, the use of Doehlert designs for the optimization of three experimental variables is proposed. Sequential response surface methodology is based on a strategy to obtain a quadratic function relationship between the response and the significant variables using a three and five-level experimental design. The Doehlert design structure allows us to study this reponse surface by estimating the parameters of the quadratic model and thus, by building sequential designs, it is possible to obtain the region in which the optimum values of such variables are simultaneously obtained. The mobility of these designs across the experimental domain of the variables permits the use of data from a previous design for a new design, obtained by response variation for the other two variables. The principle of this methodology is described and an example of its application in a spectrofluorimetric method is given.

Derivative spectrophotometric resolution of mixtures of the food colourants Tartrazine, Amaranth and Curcumin in a micellar medium.

Abstract A study of the absorption spectra of the food colourants Tartrazine (E-102), Amaranth (E-123) and Curcumin (E-100) in various organic solvents and pH media, have been carried out. In addition, the spectral behaviour in aqueous micellar systems of anionic, cationic and non-ionic surfactants, as well as β -cyclodextrin, was investigated. Analytical methods are proposed for the determination of the three dyes in mixtures without any prior separation step, by the application of the derivative technique to the normal absorption spectra, based on the use of cetyltrimethylammonium bromide (CTAB) in 0.1 M NaOH, over the concentration range 2–50 μg ml −1 . The methods are applied for determining the three dyes in commercial food products.

Micellar medium for the analysis of complex mixtures of molybdenum and tungsten by derivative synchronous spectrofluorimetry in steels

The cationic surfactant hexadecyltrimethylammonium bromide enhances the fluorescence intensity of both molybdenum and tungsten complexes obtained with Alizarin Red S. This characteristic has been used for a sensitive simultaneous spectrofluorimetric determination of both ions over the range 32-4000 ng/ml and 49-2500 ng/ml for Mo and W, respectively. Good selectivity is achieved applying the well known synchronous derivative technique with a minucious pH selection. The proposed method has been applied to a certified steel sample with recoveries between 96 and 102%.

Estimation of the Tolerance Level of Interfering Substances in Instrumental Analytical Methods

Abstract A model to estimate the tolerance level of interfering substances for analytical procedures, applying the linear simple regression, is proposed. The confidence interval on the analytical signal for the selected concentration value to check the interference, is calculated using the calibration data set. The tolerance levels of molybdenum, aluminium and iron in the spectro fluorimetric determination of boron with Alizarin Red S by means of direct, synchronous and first- and second-derivative methods, are estimated. The adequate selection of an analyte concentration for the interferent test is discussed.

Study of the mixed-metal lanthanummagnesium-purpurin complex: spectrophotometric determination of yttrium and lanthanides.

Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg(2)P(5), which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 x 10(4) l.mole(-1).cm(-1) at 570 nm and its conditional extraction constant 5 x 10(13) l(4).mole(-4). Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 mug has been investigated.

A first and straightforward approach to detection limits for narrow-bore HPLC and CE.

Two methodologies have been proposed for a simple statistical estimation of the detection limits in microbore-HPLC and CE techniques. Due to the impossibility to measure the blank, by using the extrapolated or approximated expressions it is possible to obtain a straightforward approach of the detection limits from the study of the residuals of the calibration data set, avoiding tedious treatment of the signals. The utility of these expressions has been checked on the data from an experimental microbore HPLC system.

Non-ionic micellar solubilization: spectrofluorimetric determination of trace of germanium(IV) with quercetin in real samples

A spectrofluorometric method is described for the determination of germanium(IV) based on its complexation reaction with quercetin in presence of Brij-35. The fluorescence is monitored at 552 nm with excitation at 432 nm. The pH, quercetin and Brij-35 concentrations were optimized simultaneously using the response surface methodology from sequential experimental three-variable Doehlert designs. Interferences in this determination have been studied. The detection limit is 7.4 ng ml −1 and the linear range is between 7.4 and 150 ng ml −1 . The method has been applied to the determination of germanium in a drug and in wholemeal oats.

Simultaneous spectrofluorimetric determination of traces of molybdenum and boron in plant leaves

Abstract A method is described for the simultaneous determination of molybdenum and boron in plant leaves, based on the highly sensitive fluorescence reaction with Alizarin Red S. Simplicity is achieved by using first and second derivatives of the synchronous spectra. Appropriate calibration equations were established between 0.1–0.9 and 0.3–0.7 μg ml−1 for molybdenum and boron, respectively, with a mean relative standard deviation of 2.2%.

Spectrofluorimetric determination of molybdenum in vegetal tissues and a pharmaceutical compound with Alizarin Red S in micellar medium

A sensitive method for the spectrofluorimetric determination of Mo with Alizarin Red S, in the presence of hexadecyltrimethylammonium bromide, is described. The complex is formed at pH 4.7 in micellar medium, and the fluorescence intensity develops immediately. The detection limit is 1.7 ng cm–3 and the linear range is between 6 and 1000 ng cm–3. The influence of several ions, as interferents, is discussed. The proposed method has been applied to the determination of Mo in vegetal tissues and in a pharmaceutical compound.