A. M. García Campaña

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.

Statistical estimation of linear calibration range

Abstract The “in-line” and “on-line” linearity terms of a linear calibration are defined. “On-line” linearity, which is calculated from the standard deviation of the slope, is proposed as a performance characteristic for the analytical method. The relation between the precision of an analytical result, and the analytical sensitivity and “on-line” linearity of the corresponding chemical calibration is established. The simplified equation that is obtained makes it possible to rapidly estimate the standard deviation with a sufficient degree of freedom, even when few analysis replicates are available. An indication is also given of the suitable equation for a more accurate calculation. The use of the two linearities, both “in-line” and “on-line”, is discussed, concerning the determination of the linear calibration range, for those techniques with which curvatures are obtained when the concentration of the standard analyte exceeds a particular value.

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.

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.

Microdialysis with on-line chemiluminescence detection for the study of nitric oxide release in rat brain following traumatic injury.

An on-line method was developed for the real-time detection of nitric oxide (NO) release in rat brain in vivo following traumatic injury by coupling microdialysis sampling to flow-injection chemiluminescence (CL) detection. The NO released from rat cerebellum was detected based on the CL reaction of luminol and H2O2 with a detection limit of 1 nmol l 1 . The perfusate flow was set at 5 m lm in 1 in order to minimize NO loss before reaching CL detector. With this flow rate, about 5 s was required for the solution to pass through the membrane of microdialysis probe to the detector due to the dead volume of the probe and CL cell. It was observed that the efficiency of NO penetrated from rat cerebellum into perfusate stream increased along with decrease of perfusate flow rate. The maximum efficiency of 20% could be achieved at the flow rate of 5 m lm in 1 with carefully home-made microdialysis probe. The developed method was applied to the study of the production of NO in rat cerebellum following the traumatic brain injury. The results indicated that the NO increased dramatically following traumatic brain injury and was inhibited after the injection of inhibitors such as l-arginine.

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.