Arsenio Muñoz de la Peña

Second- and higher-order data generation and calibration: a tutorial.

An introduction to multi-way calibration based on second- and higher-order data generation and processing is provided, with emphasis on practical experimental aspects. After a discussion concerning a proper nomenclature scheme, a suitable classification of the obtainable data, and the general features of the available algorithms and their underlying models, a series of examples is discussed in detail, with the purpose of illustrating the great potentiality of the field for the analytical community. Emphasis is directed toward the most popular multi-way data, i.e., second-order or matrix data, which can be conveniently measured in a variety of instruments. Third-order data are being increasingly studied and are also discussed, along with the less explored field of fourth-order data. The estimation of figures of merit, which analysts need to report during method development, is now sufficiently mature to be provided for the general audience.

Determination of salicylic acid and its metabolites in urine by derivative synchronous spectrofluorimetry

The simultaneous determination of salicylic acid in binary and/or ternary mixtures and its two main urinary metabolites is proposed. Mixtures of salicylic, salicyluric and gentisic acids are resolved by synchronous spectrofluorimetry, in combination with first-derivative measurements. The urine is extracted with diethyl ether in acid medium. Salicylic and salicyluric acids are re-extracted into glycine-sodium hydroxide buffer solution of pH 11.6 and determined at that pH, and salicylic and gentisic acids are re-extracted into boric acid-sodium hydroxide buffer solution of pH 8.5 and determined at pH 6.

Room-temperature phosphorescence of acenaphthene in aerated solutions in the presence of bromoalcohols and γ-cyclodextrin

Abstract The inclusional complexation between γ-cyclodextrin and acenaphthene in aqueous solution was investigated by spectroscopic techniques. A 1:1 complex was detected and its formation constant was determined. After adding bromoalcohols such as 2,3-dibromopropane-1-ol or 2-bromoethanol both a decrease of the fluorescence and an enhancement of the room-temperature phosphorescence (RTP) of acenaphthene were observed. The RTP signals from acenaphthene included in γ-cyclodextrin were optimized. The apparent formation constant of the ternary γ-cyclodextrin-acenaphthene-2,3-dibromopropane-1-ol complex was determined from RTP data. On the other hand, the inclusion complex formed between γ-cyclodextrin, acenaphthene and 2-bromoethanol was found to be very labile and its equilibrium constant could not be determined with accuracy. Large RTP signals were obtained in both ternary systems, even in the absence of sodium sulfite as deoxygenant agent. This fact would indicate that in these complexes the acenaphthene is protected from the action of quenchers such oxygen.

Spectrofluorimetric determination of nalidixic acid based on host–guest complexation with γ-cyclodextrin

The characteristics of host–guest complexation between γ-cyclodextrin and nalidixic acid were investigated by fluorescence spectrometry. A 1 : 1 stoichiometry of the complex was established and an association constant of 292 l mol–1 was calculated by using the changes in the fluorescence of nalidixic acid that occurred when it was included in the hydrophobic cyclodextrin cavity. A spectrofluorimetric method for the determination of nalidixic acid was developed, with a range of application between 0.1 and 2 µg ml–1. The method was applied satisfactorily to the determination of nalidixic acid in a pharmaceutical preparation and in urine.

Two Multivariate Strategies Applied to Three-Way Kinetic Spectrophotometric Data for the Determination of Mixtures of the Pesticides Carbaryl and Chlorpyrifos

Two pesticides, carbaryl and chlorpyrifos, have been simultaneously determined using second-order kinetic spectrophotometric measurements upon alkaline oxidative degradation. In spite of the complexity of the system and of the serious spectral overlap among the reagents and products, calibration and prediction is possible thanks to the power of second-order multivariate techniques. Strategies such as parallel factor analysis (PARAFAC) and multivariate curve resolution coupled to alternating least-squares (MCR-ALS) have been employed, which adequately exploit the second-order advantage. They allow for a correct determination of the analytes both in synthetic binary samples and in a commercial formulation, in this latter case even in the presence of unmodeled interferents. Multi-way partial least-squares (n-PLS) produced good results only on synthetic binary mixtures but could not be applied to a commercial sample because it contained an uncalibrated component.

Modeling four and three-way fast high-performance liquid chromatography with fluorescence detection data for quantitation of fluoroquinolones in water samples.

This paper presents a study regarding the acquisition and analytical utilization of four and three-way data, acquired by following the excitation-emission fluorescence matrices at different elution times, in a fast liquid chromatographic HPLC procedure. This kind of data were implemented for first time for quantitative purposes, and applied to the determination of two fluoroquinolones in tap water samples, as a model to show the potentiality of the proposed strategy of four-way data generation. The data were modeled with three well-known algorithms: PARAFAC, U-PLS/RTL and MCR-ALS, the latter conveniently adapted to model third-order data. The second-order advantage was exploited when analyzing samples containing uncalibrated interferences. PARAFAC and MCR-ALS were the algorithms that better exploited the second-order advantage when no peak time shifts occurred among samples. On the other hand, when the quadrilinearity was lost due to the occurrence of temporal shifts, MCR-ALS furnished the better results. Relative error of prediction (REP%) obtained were 9.9% for ofloxacin and 14.0% for ciprofloxacin. In addition, a significant enhancement in the analytical figures of merit was observed when going from second- to third-order data (reduction of ca. 70% in LODs).

Nonlinear Four-Way Kinetic-Excitation-Emission Fluorescence Data Processed by a Variant of Parallel Factor Analysis and by a Neural Network Model Achieving the Second-Order Advantage : Malonaldehyde Determination in Olive Oil Samples

Four-way data were obtained by recording the kinetic evolution of excitation-emission fluorescence matrices for the product of the Hantzsch reaction between the analyte malonaldehyde and methylamine. The reaction product, 1,4-disubstituted-1,4-dihydropyridine-3,5-dicarbaldehyde, is a highly fluorescent compound. The nonlinear nature of the kinetic fluorescence data has been demonstrated, and therefore the four-way data were processed with parallel factor analysis combined with a nonlinear pseudounivariate regression, based on a quadratic polynomial fit, and also with a recently introduced neural network methodology, based on the combination of unfolded principal component analysis, residual trilinearization, and radial basis functions. The applied chemometric strategies are not only able to adequately model the nonlinear data but also to successfully determine malonaldehyde in olive oil samples. This is possible since the experimentally recorded four-way data, modeled with the above-mentioned advanced chemometric approaches, permit the achievement of the second-order advantage. This allows us to predict the analyte concentration in a complex background, in spite of the nonlinear behavior and in the presence of uncalibrated interferences. The present work is a new example of the use of higher-order data for the resolution of a complex nonlinear system, successfully employed in the context of food chemical analysis.

Determination of marker pteridins and biopterin reduced forms, tetrahydrobiopterin and dihydrobiopterin, in human urine, using a post-column photoinduced fluorescence liquid chromatographic derivatization method

A liquid chromatographic method for the simultaneous analysis of marker pteridins and biopterin reduced forms, in urine samples is proposed. A Zorbax Eclipse XDB-C18 column was used for the chromatographic separation, using a 98/2 (v/v), citrate buffer (pH 5.5)-acetonitrile mobile phase, in isocratic mode. A post-column photoderivatization was carried out with an on-line photoreactor, located between a diode array detector (DAD) and a fast scanning fluorescence detector (FSFD). Neopterin (NEO), biopterin (BIO), pterin (PT) and dihydrobiopterin (BH2) were determined by measuring native fluorescence, using the photoreactor in OFF-mode, and tetrahydrobiopterin (BH4) was determined by measuring of the induced fluorescence of the generated photoproducts, using the photoreactor in ON-mode. In addition, Creatinine (CREA), as a reference of metabolites excrection in urine, was simultaneously determined using the DAD detector. Detection limits were 0.2, 13.0, 0.3, 0.3 and 3.5 ng mL(-1), for NEO, BH2, BIO, PT and BH4, respectively, and 0.4 microg mL(-1) for CREA. Ratio values for NEO/CREA, PT/CREA, BH4/CREA, BH2/CREA, NEO/BIO and BIO(total)/CREA, in urine samples, of healthy children and adults, phenylketonuric children and infected mononucleosis children, are reported. A comparative study, about the mean values obtained for each of the compounds, by the present procedure and by the classical iodine oxidation method (Fukushimas method), has been performed, in urine samples belonging to healthy volunteers. The values obtained were BH4/CREA: 0.41, BH2/CREA: 0.31 and BIO(total)/CREA: 0.73, by the proposed method, and BH4/CREA: 0.35, BH2/CREA: 0.20 and BIO(total)/CREA: 0.48, by iodine oxidation method.

Fluorimetric Determination of Sulfametoxazole in Pharmaceutical Preparations in Combination with Trimethoprim by Inclusion in β-Cyclodextrin/Urea

Abstract The inclusion complex of sulfametoxazole in β-cyclodextrin has been investigated. A 1:1 stoichiometry of the complex has been established and a 226 M−1 formation constant has been calculated by using the changes produced on the fluorescence of the drug when included on the hydrophobic cyclodextrin cavity. An enhancement of the fluorescence emission of sulfametoxazole and protection of the drug against photochemical reactions has been attained upon inclusion. To avoid the problem of the low solubility of β-cyclodextrin in water, solutions of β-cyclodextrin in 8 M urea have been used. A fluorimetric method of determination of sulfametoxazole has been proposed and applied in several pharmaceutical preparations containing trimethoprim, without interference from this compound.

Simultaneous determination of cobalt and nickel by first-derivative spectrophotometry

A method for the simultaneous determination of cobalt and nickel in mixtures by first-derivative spectrophotometry is described. The method is based on the red complexes formed by both metal ions with 1-hydroxy-2-carboxyanthraquinone in alkaline ethanol-water mixtures. The range of application is between 0.75 and 4.5 µg ml–1 for cobalt and between 0.50 and 3.0 µg ml–1 for nickel. A statistical evaluation of the experimental results is reported.