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A new sensitive multiresidue method based on ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) has been developed for the detection, confirmation and quantification of twenty five carbamates in wine samples. The separation was achieved in 5.5 min, using a Zorbax Eclipse plus RRHD C18 column (50 mm×2.1 mm, 1.8 μm), with a mobile phase of water and methanol, both of them with 0.01% formic acid. The analytes were detected in positive mode with multiple reaction monitoring mode. Ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME), using a low-density extraction solvent has been optimized for the satisfactory extraction of carbamates and clean-up of extracts. The matrix effect was studied, showing that the proposed procedure provides very clean extracts. Under optimum conditions, recoveries for fortified wine samples ranged from 74 to 102%, with relative standard deviations lower than 6%. Limits of quantification ranged from 0.15 to 0.92 μgl(-1), showing the high sensitivity of this fast and simple method and its compliance with current requirements., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A new analytical method based on micellar electrokinetic chromatography tandem mass spectrometry (MEKC-ESI-MS/MS) employing a MS friendly surfactant (ammonium perfluorooctanoate) is proposed and validated for the identification and simultaneous quantification of 17 N-methylcarbamate pesticides in environmental and drinking water samples. MS/MS detection using an ion trap as analyzer operating in the multiple reaction monitoring mode was used. Different parameters were optimized in order to obtain an adequate CE separation combined with the highest sensitivity in MS/MS. Dispersive liquid-liquid microextraction (DLLME) using a low-density extraction solvent has been proposed for extraction, obtaining a preconcentration factor of 10. Under optimum conditions, recoveries for fortified samples ranged from 83% to 101%, with relative standard deviations lower than 8%. The limits of detection ranged from 1 to 144 ng l⁻¹, demonstrating the sensitivity and applicability of this fast, simple, and environmentally friendly method., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The characterization and authentication of fats and oils is a subject of great importance for market and health aspects. Identification and quantification of triacylglycerols in fats and oils can be excellent tools for detecting changes in their composition due to the mixtures of these products. Most of the triacylglycerol species present in either fats or oils could be analyzed and identified by chromatographic methods. However, the natural variability of these samples and the possible presence of adulterants require the application of chemometric pattern recognition methods to facilitate the interpretation of the obtained data. In view of the growing interest in this topic, this paper reviews the literature of the application of exploratory and unsupervised/supervised chemometric methods on chromatographic data, using triacylglycerol composition for the characterization and authentication of several foodstuffs such as olive oil, vegetable oils, animal fats, fish oils, milk and dairy products, cocoa and coffee., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The present work studies the effectiveness of the use of triacylglycerols (TAGs) for the quantification of olive oil in blends with vegetable oils. The determinations were obtained using high-performance liquid chromatography (HPLC) coupled to a Charged Aerosol Detector (CAD), in combination with Partial Least Squares (PLS) regression and using interval PLS (iPLS) for variable selection. Results revealed that PLS models can predict olive oil concentrations with reasonable errors. Variable selection through iPLS did not improve predictions significantly, but revealed the chemical information important in the chromatogram to quantify olive oil in vegetable oil blends., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Dispersive liquid-liquid microextraction (DLLME) has been proposed for the extraction and preconcentration of 12 carbamate pesticides in juice samples, followed by their determination by micellar electrokinetic chromatography with diode-array detection. To improve sensitivity, an on-capillary sample concentration method based on sweeping has been developed. Also, separations were performed in an extended light path fused-silica capillary; the separation buffer consisted of 100 mM borate and 50 mM SDS (pH 9.0) with 5% acetonitrile. Samples were introduced by hydrodynamic injection, dissolved in the separation buffer, but free of micelles. Several parameters of the DLLME procedure (such as type and volume of extraction and dispersive solvents, pH, salt addition, and extraction time) were optimized. Recoveries obtained for fortified juice samples (banana, pineapple, and tomato) at three different concentration levels, ranged from 78% to 105%, with relative standard deviations lower than 9%. The limits of detection ranged from 1 to 7 μg l(-1). Moreover, the method is fast, simple, and environmentally friendly.

The ability of multivariate analysis methods such as hierarchical cluster analysis, principal component analysis and partial least squares-discriminant analysis (PLS-DA) to achieve olive oil classification based on the olive fruit varieties from their triacylglycerols profile, have been investigated. The variations in the raw chromatographic data sets of 56 olive oil samples were studied by high-temperature gas chromatography with (ion trap) mass spectrometry detection. The olive oil samples were of four different categories ("extra-virgin olive oil", "virgin olive oil", "olive oil" and "olive-pomace" oil), and for the "extra-virgin" category, six different well-identified olive oil varieties ("hojiblanca", "manzanilla", "picual", "cornicabra", "arbequina" and "frantoio") and some blends of unidentified varieties. Moreover, by pre-processing methods of chemometric (to linearise the response of the variables) such as peak-shifting, baseline (weighted least squares) and mean centering, it was possible to improve the model and grouping between different varieties of olive oils. By using the first three principal components, it was possible to account for 79.50% of the information on the original data. The fitted PLS-DA model succeeded in classifying the samples. Correct classification rates were assessed by cross-validation.

This work presents a method for an efficient differentiation of olive oil and several types of vegetable oils using chemometric tools. Triacylglycerides (TAGs) profiles of 126 samples of different categories and varieties of olive oils, and types of edible oils, including corn, sunflower, peanut, soybean, rapeseed, canola, seed, sesame, grape seed, and some mixed oils, have been analyzed. High-performance liquid chromatography coupled to a charged aerosol detector was used to characterize TAGs. The complete chromatograms were evaluated by PCA, PLS-DA, and MCR in combination with suitable preprocessing. The chromatographic data show two clusters; one for olive oil samples and another for the non-olive oils. Commercial oil blends are located between the groups, depending on the concentration of olive oil in the sample. As a result, a good classification among olive oils and non-olive oils and a chemical justification of such classification was achieved.

We have developed and validated a CE-MS/MS method using an in-line SPE device (analyte concentrator, AC) to determine eight quinolones of veterinary use whose maximum residue levels in animal edible tissues are established by the EU Council Regulation 2377/90, i.e., danofloxacin, sarafloxacin, ciprofloxacin, marbofloxacin, enrofloxacin, difloxacin, oxolinic acid, and flumequine. Different parameters affecting the AC performance, such as its design (in this case frit-free), the kind of sorbent (Oasis MCX), sample pH, volume, and composition of the elution plug and injection time were studied. The method was validated using standard solutions obtaining LODs between 17 and 59 ng/L. Finally, a pressurized liquid extraction (PLE) method was developed to determine these antibiotics in chicken muscle samples. The whole analytical method was validated in terms of linearity (r2 >or= 0.992), recoveries (63-112%), repeatability and intermediate precision (RSD

A new analytical method based on capillary zone electrophoresis-tandem mass spectrometry (CZE-MS/MS) is proposed and validated for the identification and simultaneous quantification of eight quinolones for veterinary use in bovine raw milk. The studied quinolones include danofloxacin, sarafloxacin, ciprofloxacin, marbofloxacin, enrofloxacin, difloxacin, oxolinic acid, and flumequine, whose contents are regulated by the EU Council Regulation no. 2377/90 in animal edible tissues. Different parameters (i.e., separation buffer composition and electrospray conditions) were optimized in order to obtain both an adequate CE separation and a high sensitivity, using experimental design methodology to consider the interactions among the studied variables. MS/MS experiments using an ion trap as analyzer operating in the multiple reaction monitoring mode were carried out to achieve the minimum number of identification points according to the 2002/657/EC European Decision. For the quantification in bovine raw milk samples, a two-step solid-phase extraction procedure was developed using Oasis MAX and HLB cartridges without protein precipitation. Satisfactory results were obtained in terms of linearity (r2 between 0.989 and 0.992) and precision (RSD below 18%). The limits of detection and quantification (below 6 and 24 ppb, respectively) were in all cases lower than the maximum residues limits tolerated for these compounds in milk, the recoveries ranging from 81 to 110%, indicating the potential of the CZE-MS/MS for the analysis of regulated quinolone antibiotics in the food quality and safety control areas.

A CE instrument coupled with chemiluminescence (CL) detection was designed for the determination of promethazine hydrochloride (PTH) and promazine hydrochloride (PMH) in real samples. An important enhancement of the CL emission of luminol with potassium ferricyanide was observed in the presence of these phenothiazines; so this system was selected for their detection after CE separation. Parameters affecting the electrophoretic separation were optimized in a univariate way, while those affecting CL detection were optimized by means of a multivariate approach based on the use of experimental designs. Chemometrics was also employed for the study of the robustness of the factors influencing the postcolumn CL detection. The method allows the separation of the phenothiazines in less than 4 min, achieving LODs of 80 ng/mL for PMH and 334 ng/mL for PTH, using sample injection by gravity. Electrokinetic injection was used to obtain lower LODs for the determination of the compounds in biological samples. The applicability of the CE-CL method was illustrated in the determination of PTH in pharmaceutical formulations and in the analysis of PMH in human urine, using a previous SPE procedure, achieving an LOD of 1 ng/mL and recoveries higher than 85%.

A simple and sensitive procedure for the determination of gentamicin is presented, based on the use of the peroxyoxalate chemiluminescent (PO-CL) system in presence of imidazole as a catalyst. The gentamicin has to be previously derivatized with o-phthaladehyde (OPA) in order to obtain a fluorophore, which participates in the PO reaction, producing a CL emission proportional to the gentamicin concentration. The method is developed by using a particular flow-injection analysis (FIA) manifold, employing sodium dodecyl sulfate (SDS) micellar medium as a carrier in order to avoid the degradation of PO in water. The optimization of the instrumental and chemical variables affecting the CL reaction was rigorously carried out by using experimental design methodology. The method has been successfully applied to pharmaceutical formulations.

A capillary zone electrophoresis (CZE) method with ultraviolet-visible detection has been established and validated for the determination of five phenothiazines: thiazinamium methylsulfate, promazine hydrochloride, chlorpromazine hydrochloride, thioridazine hydrochloride, and promethazine hydrochloride in human urine. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 150 mM tris(hydroxymethyl)aminomethane and 25% acetonitrile at pH 8.2, with temperature and voltage of 25 degrees C and 20 kV, respectively. Naphazoline hydrochloride was used as an internal standard. Field-amplified sample injection (FASI) has been applied to improve the sensitivity of the detection. Considering the influence of parameters affecting the on-line preconcentration (nature of preinjection plug, sample solvent composition, injection times, and injection voltage) and due to the significant interactions among them, in this paper we propose for the first time the application of a multivariate approach to carry out the study. The optimized conditions were as follows: preinjection plug of water for 7 s at 50 mbar, electrokinetic injection for 40 s at 6.2 kV, and 32 microm of H3PO4 in the sample solvent. Also, a solid-phase extraction (SPE) procedure is developed to obtain low detection limits and an adequate selectivity for urine samples. The combination of SPE and FASI-CZE-UV allows adequate linearities and recoveries, low detection limits (from 2 to 5 ng/mL), and satisfactory precisions (3.0-7.2% for an intermediate RSD %).

A simple and sensitive method has been proposed for the amikacin sulphate determination. It is based on the inhibition of the chemiluminescence (CL) emission generated from the oxidation of luminol in alkaline medium by H2O2 catalyzed by Cu(II), due to the interaction caused by amikacin, which forms a robust complex with the catalyst. The optimization of the experimental and instrumental variables affecting this CL inhibition effect has been carried out using statistical models, based on the application of two-level full factorial and Box-Behnken designs. The performance characteristics of the proposed method have been established, showing that the method is efficient to determine amikacin sulphate in the linear range of 9.89-20 mg/L with a detection limit of 2.97 mg/L. It has been successfully applied to the amikacin sulphate determination in pharmaceutical formulations.

The solubilities of benzocaine and salicylic acid were determined in water-dioxane mixtures at several temperatures (5-40 degrees C for benzocaine and 10-40 degrees C for salicylic acid). The solubility curves as a function of dioxane ratio showed a maximum at 90% dioxane at all temperatures. Above 25 degrees C, the homogeneous mixture splits into two liquid immiscible phases. For benzocaine, the initial dioxane concentration range at which phase separation takes place increased with temperature (50-60% at 25 degrees C, 50-70% at 30-35 degrees C and 40-70% at 40 degrees C). For salicylic acid, the dioxane concentration required for phase separation (40-60% dioxane) did not change with temperature. Phase separation was not related to solid phase changes (polymorphism or solvates). The phase composition and drug extraction at the drug-rich phase were determined. The apparent enthalpies of the solution process were a nonlinear function of the dioxane ratio for both drugs. The apparent enthalpy of solution of benzocaine was larger than that expected at the upper limit of phase separation (70% dioxane), whereas for salicylic acid the apparent enthalpy of solution decreased abruptly at the region corresponding to phase separation (40-70% dioxane). Both drugs showed a nonlinear pattern of enthalpy-entropy compensation.

A review of the use of the Doehlert matrix as a chemometric tool for the optimization of methods in analytical chemistry and other sciences is presented. The theoretical principles of Doehlert designs are described, including the coded values for the use of this matrix involving two, three, four and five variables. The advantages of this matrix in comparison with other response surface designs, such as central composite and Box-Behnken, designs are discussed. Finally, 57 references concerning the application of Doehlert matrices in the optimization of procedures involving spectroanalytical, electroanalytical and chromatographic techniques are considered.

Flow Injection analysis represents an attractive tool because of its great advantages, such as versatility, speed, high sampling rate and wide applicability in the field of pharmaceutical analysis. However, due to the inherent characteristics of the technique, the choice of the best set of operational and chemical conditions is complicated and the conventional univariate optimisation method present some limitations, mainly due to fact that the interdependence of variables is not considered. In relation to the calibration process, because of the transient character of the signals obtained using FIA manifolds coupled with different detection techniques, different strategies can be used in calibration to solve some problems related to the nature of the signal thereby improving the performance characteristics of the method. This paper offers an overview of different methodologies used in optimisation based on the use of statistically designed experiments and some strategies developed for calibration applied to the analysis of pharmaceuticals.

The determination of stoichiometries and stability constants of complexes by means of UV-visible spectrophotometry applying traditional methods does not evaluate the quality of the values obtained, since the classic application of these methods does not provide coverage intervals. However, the use of chemometric techniques in different steps of the application of these methods makes it possible to obtain not only a real value of the characteristics of the complexes but a validation of such a value. In this paper a methodology is proposed that combines some traditional methods, three different regression models (LMSR, LSR and LSPR) and a small number of mathematical algorithms. This methodology is able to estimate, in a simple and rigorous way, the stoichiometry and stability constant of a complex and its corresponding uncertainties.

A system for on-line preconcentration and determination of lead by flame atomic absorption spectrometry (FAAS) was proposed. It was based on the sorption of lead(II) ions on a minicolumn of polyurethane foam loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM). The optimisation step was carried out using two-level full factorial and Doehlert designs for the determination of the optimum conditions for lead preconcentration. The proposed procedure allowed the determination of lead with a detection limit of 2.2 microg L(-1), and a precision, calculated as relative standard deviation (RSD), of 2.4 and 6.8 for a lead concentration of 50.0 and 10.0 microg L(-1), respectively. A preconcentration factor of 45 and a sampling frequency of 27 samples per hour were obtained. The recovery achieved for lead determination in the presence of several cations demonstrated that this procedure has enough selectivity for analysis of environmental samples. The validation was carried out by analysis of certified reference material. This procedure was applied to lead determination in natural food.

A study on using non-parametric statistical methods was carried out to calculate the binding constant of an inclusion complex and to estimate its associated uncertainty. First, a correct evaluation of the stoichiometry was carried out in order to ensure an accurate determination of the binding constant. For this purpose, the modified Benesi-Hildelbrand method had been previously applied. Then, four statistical methods (three non-parametric methods: two bootstrap approaches, the jackknife method and a parametric one: Fieller's theorem) were employed in order to compute the binding constant. The results obtained from applying these methods and the combination of the methods: jackknife after bootstrap and bootstrap after jackknife were compared. The best results in terms of accuracy were obtained from the application of a bootstrap method: the resampling residuals approach. These procedures were applied to the inclusion complex 2-hydroxil-propyl-beta-cyclodextrin-2,4-dichloro-phenoxyacetic, which shows photochemically-induced fluorescence.

In this paper, a combination of a flow injection analysis (FIA) system with micellar-enhanced photochemically induced fluorescence (MEPIF) detection is presented as a powerful alternative for the rapid and sensitive analysis of chlorophenoxyacid herbicides. These compounds do not show native fluorescence but they can be photolysed into strongly fluorescence photoproducts after direct irradiation with ultraviolet light. The use of a cationic surfactant such as cetyltrimethylammonium chloride (CTAC) provides a considerable enhancement of photochemically induced fluorescence intensity and the nature of the technique allows a possible and easy adaptation to a FIA system. In this sense, parameters related to the nature of the analytical signal (pH, irradiation times, surfactant concentration) and to the FIA manifold (injection volume, flow rate and reactor length) have been optimised. Linear calibration graphs, with three replicates for each concentration value were established in the range of 0.2-5.0 mug ml(-1) for 2,4-Dichlorophenoxyacetic acid (2,4-D) and 0.1-5.0 mug ml(-1) for Mecoprop (MCPP). The IUPAC detection limits were 73.2 and 33.5 ng ml(-1) for 2,4-D and MCPP, respectively. Satisfactory recoveries were obtained in the analysis of these herbicides in spiked waters.

Sequential response surface methodology is a general procedure to re-optimize common analytical methods on the basis of the application of the response surface methodology and of a new approach to the steepest ascent method. This procedure, which is easy to apply, consists of estimating an analytical function relating the response with the experimental parameters by means of a second-degree polynomial. Thus, a 2nd order design covering the total experimental domain is used and when a maximum is obtained, the characteristics of the response surface are confirmed using a new design, which is obtained contracting the first one. In the proposed methodology, Box-Behnken designs are used because they offer advantages in comparison with second order designs more frequently used in the steepest ascent method (central composite designs), i.e. fewer experiments are needed, they are more efficient, they can be moved through the experimental domain and they can even be easily contracted or expanded.

Imidazole buffers were found to interfere with the determination of soluble proteins using Lowry's classical method. The influence of the constituent elements of the buffer on the calibration line was studied statistically. By combining the data corresponding to different experimental sequences, interserial calibration curves for different concentrations of imidazole buffer (10-30 mM) were obtained. The absorbance-buffer volume dependence curves produced a good fit to second-order polynomials. The accuracy of protein determination in a medium with imidazole buffer, using appropriate calibration curves, were tested by comparison with the technique of multiple standard addition and by means of recovery studies. These experiments were performed on chick brain homogenate samples. Other important aspects of validation, such as sensitivity and accuracy, were also studied.

A method is described for the determination by solid phase spectrophotometry (SPS) of trace amounts of vanadium in natural water and crude petroleum samples. The procedure is based on fixation on a dextran-type anion exchanger of the complex V(IV)-Eriochrome Cyanine R. The absorbance of the gel, at 563 and 750 nm, packed in a 1 mm cell, is measured directly. Vanadium can be determined in the 0.6-25.0 mug l(-1) range with a relative standard deviation of 2.2%. The comparison of the SPS method and the gallic acid persulphate method shows that the linearity, analytical sensitivity and precision were better for the SPS method, and that the latter method has lower detection and quantification limits than the gallic acid persulphate method.