Silvia Sanllorente

Application of an Optimization Procedure for the Determination of Chromium in Various Water Types by Catalytic‐Adsorptive Stripping Voltammetry

A procedure for the determination of chromium by differential pulse catalytic-adsorptive stripping voltammetry (DPAdSV), using N-(2-hydroxyethyl) ethylenediamine-N, N ′, N ′-triacetic acid (HEDTA) as complexing agent, has been optimized. The selection of the experimental conditions was made using experimental design methodology. The calibrations were made under these conditions, using a robust regression method which allows for the elimination of anomalous points. The detection limit obtained was 1.84×10−10 mol dm−3. The procedure was successfully applied to the determination of chromium in different water types.

Optimization of digestion procedure for the determination of nickel in wine by differential-pulse adsorptive stripping voltammetry

A method for the determination of nickel in wine by differential-pulse adsorptive stripping voltammetry using dimethylglyoxime as complexing agent was optimised using experimental design methodology. In order to destroy organic matter, two different methods of treating the sample were considered. The UV irradiation method was selected and optimised for a smaller degree of uncertainty. The recovery factor obtained with five replicates was 1.02 ± 0.05.

Electrochemical Behavior of Menadione on Glassy Carbon Rotating Disk Electrode (RDE)

The 2-methyl-1,4-naphthoquinone electrochemical behavior on glassy carbon rotating disk electrode has been the focus of this study. In order to obtain the best results, the optimal conditions for this voltammetric study have been determined, by performing a chemometric analysis of the data. The influence of five factors on the diffusion current has been studied, finding that the greatest effect is due to three of them. The optimum values for all of these parameters were: pH 7, v (potential sweep rate)=87.1 mV/s, Cmet (methanol concentration)=4.14 %(v/v), teq (equilibrium time)=2.5 min, and tdea (purge time)=2 min. These data were used to determine the mass transfer parameters: diffusion coefficient (D=(1.4±0.3)×10–4 cm2/s) and diffusion layer thickness (δ=(6.6±0.5)×10–3 cm), the kinetic parameters: charge transfer constant (K0=2.91×10–6 cm/s) and charge transfer coefficient (α=0.248), and the standard potential (E0=0.083±0.011 V).

Chapter 2 – Usefulness of PARAFAC for the Quantification, Identification, and Description of Analytical Data

Abstract Numerous research activities generate data that are organized as a three-way tensor, which can be described with PARAFAC. This chapter starts by briefly describing the PARAFAC model and the properties that support its practical utility. Besides, two alternative models are presented, PARAFAC2 and Tucker3, which are useful when the data are inconsistent with the PARAFAC model. The properties are illustrated throughout four cases that consider different analytical scenarios: (1) quantification of a target analyte in presence of interferents (excitation-emission fluorescence spectra); (2) quantification and identification of an analyte for regulated analyses ensuring the probabilities of false positive and false negative, even in the presence of interferents (gas chromatography-mass spectrometry data for pesticides); (3) prediction of a quantitative response with no specific signals (electronic nose data to predict storage time); and (4) description of a complex temporal process (for deciding on harvesting grapes).

Multivariate detection capability using a neural classifier for nonselective signals

Abstract A new methodology is proposed based on a neural network to determine the detection capability of an analytical procedure, in complex matrices, with the evaluation of the probability of false detection, α , and false nondetection, β , according to the ISO norms. This methodology is designed for first or greater order signals for which there is currently no procedure with these characteristics, which makes it difficult to use these signals in analytical procedures standardized according to the ISO norm. The procedure consists of: (i) an experimental design suited to the increase in analyte to be detected from a threshold level; (ii) a homogenisation of the multivariate signals by a Piecewise Direct Standardization (PDS) transformation; (iii) the training of a neural network with stochastic learning, Genetic Inside Neural Network (GINN), which optimises α and β directly. The procedure was applied to the polarographic determination of Tl(I)/Pb(II) mixtures and indomethacin/tenoxicam mixtures. In the first case one can assure the detection of 1 mM (threshold: 12 mM) with α and β less than 5% for both metals. While for tenoxicam it is possible to detect less than 10% of 12 mM (threshold) with α β α and β less than 5%.

Easy-to-use procedure to optimise a chromatographic method. Application in the determination of bisphenol-A and phenol in toys by means of liquid chromatography with fluorescence detection

Legal limits for phenol and bisphenol-A (BPA) in toys are 15 and 0.1 mg L-1 respectively. The latest studies show that in Europe the content of BPA, which reaches our bodies through different contact routes, in no cases exceed legal limits. But it is true that the effects caused by continued intake of this analyte for a long time and other possible processes that could increase their migration, are still under consideration by the health agencies responsible. A multiresponse optimization using a D-optimal design for simultaneously optimising two experimental factors (temperature and flow) at three levels and one (mobile phase composition) at four levels, in the determination by means of HPLC-FLD is proposed in this work. The D-optimal design allows ones to reduce the experimental effort from 36 to 11 experiments guaranteeing the quality of the estimates. The model fitted is validated and, after the responses are estimated in the whole experimental domain, the experimental conditions that maximize peak areas and minimize retention times for both analytes are chosen by means of a Pareto front. In this way, the sensitivity and the time of the analysis have been improved with this optimization. Decision limit and capability of detection at the limits obtained were 33.9 and 66.1 μg L-1 for phenol and 25.6 and 50.0 for BPA μg L-1 respectively when the probabilities of false negative and false positive were fixed at 0.05. The procedure has been successfully applied to determine phenol and BPA in different samples (toys, clinical serum bags and artificial tears). The simulants HCl 0.07 M and water were used for the analysis of toys. The quantity of phenol found in serum bags and in artificial tears ranged from 15 to 600 μg L-1. No BPA has been found in the objects analysed. In addition, this work incorporates computer programmes which implement the procedure used (COOrdinates parallel plot and Pareto FROnt, COO-FRO) such that it can be used in any other chromatographic optimization.

Impact of time and temperature of storage on the spoilage of swordfish and the evolution of biogenic amines through a multiway model

A new multiway/multivariate approach is proposed to study and model the spoilage of swordfish with time and temperature of storage through the profiles of putrescine, spermidine, histamine, tyramine, tryptamine, cadaverine, spermine, and 2‐phenylethylamine. The evolution of these biogenic amines in food is a complex process that cannot be characterized by a single parameter but by a modification of the amine profiles. An experimental strategy is designed to determine these profiles in such a way that data are structurally 3‐way. Modeling the joint evolution of the biogenic amines with a PARAFAC model which explains 97.8% of variability (CORCONDIA index equals 100%) leads to estimate the storage time, storage temperature, and biogenic amines profiles. A multiple regression (determination coefficient of 0.98) based on the loadings of the 2 factors of the time profile of the PARAFAC model enables the estimation of the storage time with an error of 0.5 days.