Monitoring winemaking process using tyrosine influence in the excitation-emission matrices of wine.

Wine samples collected during the winemaking process have been analyzed employing a previously optimized UHPLC-FD method, determining their biogenic amines and amino acids profile. The results obtained have been submitted to a statistical analysis from which it was extracted that the most influential analyte was tyrosine. Thanks to its fluorescence, a method for its determination by excitation-emission matrices has been proposed. The accuracy of the method has been checked by means of Elliptical Joint Confidence Region test. The winemaking process has been monitored with this method, obtaining a faster and cheaper way to follow the process.

Exploring the potential of combining chemometric approaches to model non-linear multi-way data with quantitative purposes - A case study.

Second-order based calibration methods have been widely investigated capitalizing on the inherent benefits of the data structure and the decomposition models, demonstrating that second-order advantage is a property that conspires to a high likelihood success in the resolution of systems of varying complexity. This work aims to demonstrate the applicability of a combined chemometric strategy to solve non-linear multivariate calibration systems in the presence of non-multilinear multi-way data. The determination of histamine by differential pulse voltammetry at different pH is presented as case study. The experimental system has the outstanding difficulty arisen from the large displacement along the potential axis by the pH, which was successfully overcome by implementation of the presented combined strategy. For data modeling, MCR-ALS, U-PLS/RBL and U-PCA/RBL-RBF were used. MCR-ALS allowed unraveling the non-linear behavior between the signal and the concentration, and extracting the underlying profiles of the constituent. Quantitative analysis was performed through the three models, and a comparative evaluation of the predictive performance was done. The best results were achieved with U-PCA/RBL-RBF (mean recovery = 101%) whereas, MCR-ALS yield the lowest mean recovery for all samples (70%).

Automated chromatographic method with fluorescent detection to determine biogenic amines and amino acids. Application to craft beer brewing process.

The combined determination of biogenic amines and amino acids is a challenge for food scientists. In this research, a new methodology for the automatic on-line precolumn derivatization and determination of 8 biogenic amines and 9 precursor amino acids by Ultra-High Performance Liquid Chromatography with fluorescent detection has been developed. The method derivatized the analytes with o-phthaldialdehyde and achieved the separation of the 17 derivatives in less than 15 min, obtaining good quality parameters (limits of detection varied between 7.00 and 210 µg L-1, and RSD intraday ranged between 1.5 and 6.0%). The optimization of the derivatization procedure has been carried out employing an experimental design and the Surface Response Methodology. The method has been validated and applied to wine and beer, obtaining good recuperation percentages (72.3-138.4%). Also, samples collected during the fermentation of a craft beer, as well as a bottled sample of the same batch, have been analyzed, to monitor the changes in the profile of biogenic amines and amino acids.

Dispersive liquid-liquid microextraction for a rapid determination of glyoxal in alcoholic beverages.

Carbonyl compounds, like glyoxal, methylglyoxal, diacetyl or pentane-2,3-dione, among others, have been widely studied. Besides its endogenous origin, they are originated from foodstuffs and are related to sensorial characteristics in products such as wine and beer. Generally, for their determination, the analytes must be derivatised to adapt them for the detection system and this step takes long time. The main aim of this research was to develop a simultaneous derivatization and extraction method which takes place in only few minutes. 3,4-diaminopyridine, as derivatizing reagent, generate a fluorescent product. This reaction is selective for glyoxal. For this new dispersive liquid-liquid microextraction (DLLME) procedure combined with chromatographic determination of glyoxal, various parameters affecting the extraction were optimized and finally, a mixture of butan-1-ol as dispersant solvent and dichloromethane as extractant solvent were selected. Its chromatographic peak appears at 2.6min. Four Spanish wines and five Spanish beers have been analysed and the results showed that the levels of glyoxal are comprised between 2.8-9.5mgL-1. The proposed DLLME method drastically reduces the reaction time from 2 or 3-20min improving the methods found in the literature. The glyoxal concentration found in the wines and beers analysed do not suppose any health risk.

Novel HPLC--Fluorescence methodology for the determination of methylglyoxal and glyoxal. Application to the analysis of monovarietal wines "Ribera del Guadiana".

The determination and quantification of α-dicarbonyl compounds, glyoxal and methylglyoxal, in "Ribera del Guadiana" monovarietal wines (Extremadura, Spain) without sample clean-up has been carried out by HPLC with spectrofluorimetric detection (307/371 nm). For this purpose, a derivatization step with the new reagent 3,4-diaminopyridine at pH 2 during 120 min at 90 °C has been included. Afterwards, the sample could be injected in the chromatographic system with no clean-up, during a total run time of 4 min. Several monovarietal wines (white, rosé and red) have been analyzed and the levels of these compounds for white wines were between 0.4-1.0 mg L(-1) glyoxal and 0.8-1.3 mg L(-1) methylglyoxal; and between 0.8-3.0 mg L(-1) and 0.5-1.8 mg L(-1) of glyoxal and methylglyoxal respectively, in red wines.

Determination of tricyclic antidepressants in human breast milk by capillary electrophoresis.

A method for the determination of several tricyclic antidepressants (imipramine, desipramine, amitriptyline, nortriptyline, clomipramine, norclomipramine, doxepine and nordoxepine) in breast milk has been developed. This assay consists of a common extraction process in an organic phase, which is evaporated until dried and finally reconstituted in the appropriate buffer for injection in a capillary electrophoresis system. The capillary electrophoresis method used is an "acetonitrile stacking" method previously reported for determining these drugs in serum samples. The method developed was applied to the analysis of these compounds in human breast milk at different concentration levels (50, 100 and 200 ppb of the TCAs hydrochlorides). An interference study of some ansiolitic drugs such as lorazepam and alprazolam was made.

Comparative study of different approaches to the determination of robustness for a sensitive-stacking capillary electrophoresis method. Estimation of system suitability test limits from the robustness test.

A robustness study for a sensitive-stacking capillary electrophoresis method based on "acetonitrile-stacking" was carried out. Ten variables (pH, acetonitrile and triethanolamine in the buffer, injection time, injection pressure, acetonitrile and NaCl in the sample, capillary and tray temperature and separation voltage), whose levels were varied by 10% around the nominal level, were examined by a Plackett-Burman design (two-level design). The effects on corrected peak area and resolution (responses) were calculated and interpreted using three statistical approaches: dummy variables, distribution effects (Dong's algorithm) and calibration curve. Dong's method was found to be the most suitable to evaluate the robustness, since it considers qualitative (resolution) and quantitative (corrected peak area) responses and does not need a minimum number of dummy variables in the experimental design. From these studies, we can deduce that the first four variables were significant at 10% around the nominal level, and therefore a new design was made with those four variables at 5% nominal level. Then, only two variables proved to be significant for the resolution between some peaks, so the system suitability test limits were defined for these resolutions.

Response surface methodology in the development of a stacking-sensitive capillary electrophoresis method by field-amplified injection for the analysis of tricyclic antidepressants in the presence of salts.

The work presented here explores the possibilities of the electrokinetic injection (EK) to achieve sensitive methods for the determination of tricyclic antidepressants in biological samples (serum). The addition of ACN to the sample, with high content in salts, causes stacking at the tip of the capillary, in a similar way as for hydrodynamic injection. An experimental design with the response surface methodology has been used to find the optimum composition of the matrix of the sample (sodium chloride and ACN percentages) and the conditions for the EK (water-plug length, time, and voltage of injection) in few experiments. The composition of the separation buffer was the same as utilized in a previous paper. The use of a bubble capillary to reach lower detection limits implies a loss of the resolution and requires a new optimization. Finally, a comparison between electrokinetic and hydrodynamic injections is made.

Response surface methodology in the development of a stacking-sensitive capillary electrophoresis method for the analysis of tricyclic antidepressants in human serum.

Stacking methods are very important in overcoming the poor detection limits in capillary electrophoresis (CE). In this paper, the separation and determination of several tricyclic antidepressants by a stacking method is described. The inclusion of acetonitrile (ACN) in the sample causes stacking (transient pseudoisotachophoresis) especially in presence of sodium chloride. An experimental design (central composite design) together with the response surface methodology has been used to find the optimum composition of the separation buffer and the optimal stacking conditions in few experiments. The response functions used are the product of the total resolution by the number of peaks, for the optimization of the separation buffer, and the product of the total resolution by the mean of the peak heights, for the optimization of the stacking conditions. About 28% of the capillary volume is loaded with sample. The calibration curves are linear over the working range (50-300 ng/mL). With a bubble capillary, the limits of detection (LODs) are in the order of 5 ng/mL. For the analysis of serum samples, enrichment with sodium chloride and the protein precipitation with ACN are enough to avoid interferences and to get stacking. Recoveries between 91.6 and 104% and RSD between 0.6 and 12% are obtained in the analysis of samples of lyophilized human serum and non-lyophilized human serum, spiked with the drugs.

Response surface methodology for the optimisation of flow-injection analysis with in situ solvent extraction and fluorimetric assay of tricyclic antidepressants.

A semiautomatic extraction-fluorimetric method for the determination of tricyclic antidepressant drugs (TCAs) based in the formation of ion pairs with 9,10-dimethoxyanthracene-2-sulphonate (DMAS) has been developed. The aqueous solutions of the TCAs (imipramine, desipramine, amitriptyline, nortriptyline, clomipramine or doxepine) are injected into a carrier composed by DMAS in an acid medium and the ion pair formed is extracted into dichloromethane where the fluorescence is measured. An experimental design (Central Composite Design) together with the Response Surface Methodology has been used to find the optimal instrumental FIA and chemical variables. We have considered as the response function the product of the peak height by the sampling frequency. The calibration curves were linear over the working range (0.25-3.00mgL(-1)). The limits of detection were lower than 0.30mgL(-1). The method has been satisfactorily applied to the determination of imipramine, amitriptyline, clomipramine and doxepin in pharmaceutical preparations.

Selective extraction and determination of multiclass pesticide residues in post-harvest French beans by low-pressure gas chromatography/tandem mass spectrometry.

A selective and reliable extraction procedure was developed and validated to determine multiclass pesticide residues in lyophilized agricultural plants by low-pressure gas chromatography coupled with tandem mass spectrometry. The method is based on a rapid and simple extraction of the lyophilized sample with dichloromethane. The results were compared with those obtained by using fresh and naturally dried samples. Slightly better recoveries and precision values were obtained for the lyophilized samples. The application of the proposed methodology was tested by analyzing French bean plants from an agricultural area of Almería (Spain). The availability of this methodology, which is capable of detecting a high number of analytes in a single analysis, has priority in analyses for a large number of pesticides used on individual commodities.