Marcello G. Trevisan

Combining standard addition method and second-order advantage for direct determination of salicylate in undiluted human plasma by spectrofluorimetry

Second-order advantage turns possible a determination in the presence of unknown interferences. This work presented an application of the second-order advantage provided by parallel factor analysis (PARAFAC). The aim was the direct determination of salicylic acid (SA), the main product of aspirin degradation, in undiluted human plasma by spectrofluorimetry. The strategy of this analysis combined the use of PARAFAC, for extraction of the pure analyte signal, with the standard addition method, for a determination in the presence of a strong matrix effect caused by the quenching effect of the proteins present in the plasma. For each sample, four standard additions were performed, in triplicates. A specific PARAFAC model was built for each triplicate of each sample, from three-way arrays formed by 436 emission wavelengths, 7 excitation wavelengths and 5 measurements (sample plus 4 additions). In all the cases, the models were built with three factors and explained more than 99.90% of the total variance. The obtained loadings were related to SA and two background interferences. The scores related to SA were used for a linear regression in the standard addition method. Good results were obtained for determinations in the SA concentration range from 3.0 to 24.0mugml(-1), providing errors of prediction between 0.7 and 6.3%.

Three-way chemometric method study and UV-Vis absorbance for the study of simultaneous degradation of anthocyanins in flowers of the Hibiscus rosa-sinensys species

Ultraviolet-visible spectra of flower extracts of the Hibiscus rosa-sinensys L. var. regius maximus species have been measured between 240.02 and 747.97nm at pH values ranging from 1.1 to 13.0. Deconvolution of these spectra using the Parallel Factor Analysis (PARAFAC) model permitted the study of anthocyanin systems without isolation and purification of the individual species. Seven species were identified: flavilium cation, carbinol, quinoidal base, and E and Z-chacone and their ionized forms. The concentration changes of flavilium cation, quinoidal basen, and E and Z ionized chalcones were determined as function of pH at the different wavelengths. The flavilium cation, quinoidal base, and ionized E-clacone are involved in tho stage kinetic processes, a fast one followed by a slower one. Ionized Z-chalcone obeys a simple first-order processes. The spectral profiles recovered by PARAFAC model are in excellent agreement with bands of experimental spectra reported in the literature for the individual species measured at specific pH values. These results complement those obtained using chemical and simple mathematical techniques and demonstrate how chemometric methods can resolve problems for complex systems.

Prediction of embryo implantation potential by mass spectrometry fingerprinting of the culture medium

This study has evaluated the performance of a multivariate statistical model to predict embryo implantation potential by processing data from the chemical fingerprinting of culture medium samples used for human embryo culture. The culture medium for 113 embryos from 55 patients undergoing ICSI was collected after embryo transfer. The samples were split into positive (n=29) and negative (n=84) implantation groups according their implantation outcomes (100% or 0% implantation). The samples were individually diluted and analyzed by electrospray ionization mass spectrometry (ESI-MS). The m/z ratios and relative abundances of the major ions in each spectrum were considered for partial least square discriminant analysis. Data were divided into two subsets (calibration and validation), and the models were evaluated and applied to the validation set. A total of 5987 ions were observed in the groups. The multivariate statistical model described more than 82% of the data variability. Samples of the positive group were correctly identified with 100% probability and negative samples with 70%. The culture media used for embryos that were positive or negative for successful implantation showed specific biochemical signatures that could be detected in a fast, simple, and noninvasive way by ESI-MS. To our knowledge, this is the first report that uses MS fingerprinting to predict human embryo implantation potential. This biochemical profile could help the selection of the most viable embryo, improving single-embryo transfer and thus eliminating the risk and undesirable outcomes of multiple pregnancies.

Evolving factor analysis-based method for correcting monitoring delay in different batch runs for use with PLS: On-line monitoring of a transesterification reaction by ATR-FTIR

In this work, the base-catalyzed transesterification of soybean oil with ethanol was monitored on-line using mid-infrared spectroscopy (MIRS) and the yield of fatty acid ethyl esters (biodiesel) was obtained by (1)H NMR spectroscopy. The MIRS monitoring carried out for 12min, was performed using a cylindrical internal reflectance cell of PbSe in the range of 3707-814cm(-1) with eight co-added scans. Two different data treatment strategies were used: in the first, the models were built using the raw data and in the other, evolving factor analysis (EFA) was used to overcome the sensor time delay due to the on-line analysis, producing significantly better results. In addition, models based on partial least squares (PLS) using three batches for calibration and another for validation were compared with models with just one batch for calibration and three for validation. The models were compared between each other using root mean square error of prediction (RMSEP) and root mean square prediction difference (RMSPD), obtaining relative errors under 3%.

Electrothermal atomic absorption spectrometric determination of lead, cadmium, copper and zinc in high-salt content samples after simultaneous separation on polyethylene powder impregnated with 1-(2-pyridylazo)-2-naphthol: application to the analysis of hemodialysis fluids

A simultaneous separation and preconcentration of lead, cadmium, zinc and copper from high-salt content matrices for subsequent electrothermal atomic absorption spectrometric determination was developed. The metals were preconcentrated on a micro-column filled with polyethylene powder impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. The determinations, without the interference of the saline matrix, were carried out after metals elution with a small volume of an ethanolic solution of nitric acid. The saline matrices were sodium, potassium, magnesium and calcium chlorides, sodium acetate and bicarbonate, which constitute concentrates for hemodialysis. The immobilisation capacity of the complexing agent is about 2.5 µmol per gram of polyethylene and the column capacity with respect to each metal is about 0.75 µmol per gram resin for copper, cadmium and zinc and 0.25 µmol per gram for lead. For the optimisation of the procedure, effects of sample flow rate and pH, eluent composition and concentration, and the influence of salts on the complexation of the metals were investigated. The proposed method was characterised by a precision of about 95% (n = 3) and recoveries from spiked samples of the salts were 81–112%. All results were in agreement with those obtained by anodic stripping voltammetry, the technique used for comparison. The method was applied to the analysis of saline concentrates for hemodialysis, where the investigated metals were found in concentrations between 3.1 µg l–1 for cadmium and 90.5 µg l–1 for zinc.

Direct determination of ephedrine intermediate in a biotransformation reaction using infrared spectroscopy and PLS

Fourier transform mid-infrared spectroscopy (FT-MIR) coupled with a homemade attenuated total reflectance (ATR) flow-cell was used for on-line monitoring of a biotransformation reaction. The reaction was also monitored off-line by gas chromatography-mass spectrometry (GC-MS) enabling to establish a multivariate model for the infrared data based on partial least squares (PLS) regression. The method developed allowed the simultaneous determination of the substrate, two intermediates and the final product involved in the reduction reaction of 1-phenyl 1,2-propanedione at an initial concentration of 0.5% (v/v). The reaction was accomplished with a whole-cell suspension of Saccharomyces cerevisiae in a phosphate buffer of pH 3.0 at 32+/-1 degrees C. The ATR infrared monitoring was performed directly on the suspension cell without any separation process or extraction over 3h, totaling 188 spectra. The data were split into two subsets, with 158 times for calibration and 30 times for validation. The results showed that the proposed method may be used for on-line monitoring of the biotransformation reactions when the initial concentration is very low.

QUÍMICA ANALÍTICA DE PROCESSOS

Process Analytical Chemistry (PAC) is an important and growing area in analytical chemistry, that has received little attention in academic centers devoted to the gathering of knowledge and to optimization of chemical processes. PAC is an area devoted to optimization and knowledge acquisition of chemical processes, to reducing costs and wastes and to making an important contribution to sustainable development. The main aim of this review is to present to the Brazilian community the development and state of the art of PAC, discussing concepts, analytical techniques currently employed in the industry and some applications.

PARAFAC: uma ferramenta quimiométrica para tratamento de dados multidimensionais. Aplicações na determinação direta de fármacos em plasma humano por espectrofluorimetria

Since the last decade, the combined use of chemometrics and molecular spectroscopic techniques has become a new alternative for direct drug determination, without the need of physical separation. Among the new methodologies developed, the application of PARAFAC in the decomposition of spectrofluorimetric data should be highlighted. The first objective of this article is to describe the theoretical basis of PARAFAC. For this purpose, a discussion about the order of chemometric methods used in multivariate calibration and the development of multi-dimensional methods is presented first. The other objective of this article is to divulge for the Brazilian chemical community the potential of the combination PARAFAC/spectrofluorimetry for the determination of drugs in complex biological matrices. For this purpose, two applications aiming at determining, respectively, doxorrubicine and salicylate in human plasma are presented.

Chromatographic determination of riboflavin in the presence of tetracyclines in skimmed and full cream milk using fluorescence detection

An easy and simple chromatographic method for the determination of riboflavin in bovine milk in the presence of tetracyclines was established. For this, the proteins were precipitated with trichloroacetic acid and the separation was carried out by reversed-phase HPLC with fluorescence detection. A C8 column was used with isocratic flow using a mobile phase consisting of 0.1 mol L-1 sodium acetate, 35 mmol L-1calcium chloride and 25 mmol L-1 EDTA : methanol (65:35 v/v). The method was validated by means of the following parameters: linearity (0.9980), linear range (0.50 - 1.30 µg mL-1), intra- and inter-assay precision (RSD < 0.5%), accuracy (recovery 92%), and detection and quantitation limits (0.75 µg mL-1 and 0.22 µg mL-1, respectively). The method was applied for analysis of full cream and skimmed milk, showing robustness in the presence of tetracyclines, and when compared with a spectrofluorimetric method showed no significant difference (p < 0.05) between the results obtained.

Mapping the polymorphic forms of fexofenadine in pharmaceutical tablets using near infrared chemical imaging

This study presents a comparison of partial least squares (PLS) and multivariate curve resolution (MCR-ALS) in the quantification of polymorphic forms I and II of fexofenadine. HCl in pharmaceutical tablets using near infrared chemical imaging (NIR-CI). The PLS model built using a standard normal variate (SNV) pre-processing method resulted in satisfactory fits between the reference and predicted values, with a root mean square error of prediction (RMSEP) for both polymorphic forms below 1.5% (w/w). The MCR-ALS results were obtained using an augmented matrix and SNV pre-processing method. The lack of fit value for decomposition was 0.13%, the correlation coefficient between the pure spectra and the obtained spectral profiles was 99.94% and the RMSEP was below 6% (w/w). The MCR-ALS model efficiently quantified the polymorphic forms and generated distribution maps; however, the PLS model exhibited better recovery of the concentrations.