Recomendações para calibração em Química Analítica parte 2: calibração multianalito

This paper is a translation of an IUPAC document by K. Danzer, M. Otto and L. A. Currie (Pure Appl. Chem., 2004, 76(6), 1215-1225). Its goal is to establish a uniform and meaningful standard for terminology (in Portuguese), notation, and formulation concerning multispecies calibration in analytical chemistry. Calibration in analytical chemistry refers to the relation between sample domain and measurement domain (signal domain) expressed by an analytical function x = f s (Q) representing a pattern of chemical species Q and their amounts or concentrations x in a given test sample and a measured function y = f (z) that may be a spectrum, chromatogram, etc. Simultaneous multispecies analyses are carried out mainly by spectroscopic and chromatographic methods in a more or less selective way. For the determination of n species Qi (i=1,2, ..., n), at least n signals must be measured which should be well separated in the ideal case. In analytical practice, the situation can be different.

Firma Electrónica para Dispositivos Móviles, en la nube Nombre Estudiante:

El desarrollo de este trabajo se basa en el análisis de los diferentes tipos de certificados digitales para la tecnología en la Nube y adicionalmente se realiza una recomendación para que se implemente en Ancert una herramienta comercial de firma electrónica.

Estado da arte de figuras de mérito em calibração multivariada

The validation of an analytical procedure must be certified through the determination of parameters known as figures of merit. For first order data, the acuracy, precision, robustness and bias is similar to the methods of univariate calibration. Linearity, sensitivity, signal to noise ratio, adjustment, selectivity and confidence intervals need different approaches, specific for multivariate data. Selectivity and signal to noise ratio are more critical and they only can be estimated by means of the calculation of the net analyte signal. In second order calibration, some differentes approaches are necessary due to data structure.

Validação da metodologia da avaliação de incerteza em curvas de calibração melhor ajustadas por polinômios de segundo grau

The most widespread literature for the evaluation of uncertainty - GUM and Eurachem - does not describe explicitly how to deal with uncertainty of the concentration coming from non-linear calibration curves. This work had the objective of describing and validating a methodology, as recommended by the recent GUM Supplement approach, to evaluate the uncertainty through polynomial models of the second order. In the uncertainty determination of the concentration of benzatone (C) by chromatography, it is observed that the uncertainty of measurement between the methodology proposed and Monte Carlo Simulation, does not diverge by more than 0.0005 unit, thus validating the model proposed for one significant digit.

Determinação de sibutramina em formas farmacêuticas através de espectroscopia no infravermelho com refletância difusa e métodos de calibração multivariada

The goal of this work is the development and validation of an analytical method for fast quantification of sibutramine in pharmaceutical formulations, using diffuse reflectance infrared spectroscopy and partial least square regression. The multivariate model was elaborated from 22 mixtures containing sibutramine and excipients (lactose, microcrystalline cellulose, colloidal silicon dioxide and magnesium stearate) and using fragmented (750-1150/ 1350-1500/ 1850-1950/ 2600-2900 cm-1) and smoothing spectral data. Using 10 latent variables, excellent predictive capacity were observed in the calibration (n=20, RMSEC=0.004, R= 0.999) and external validation (n=5, RMSEC= 9.36, R=0.999) phases. In the analysis of synthetic mixtures the precision (SD=3,47%) was compatible with the rules of the Agencia Nacional de Vigilância Sanitária (ANVISA-Brazil). In the analysis of commercial drugs good agreement was observed between spectroscopic and chromatographic methods.

Reator de UV-Ozônio com lâmpada a vapor de mercúrio a alta pressão modificada para tratamento superficial de óxidos transparentes condutivos utilizados em dispositivos poliméricos eletroluminescentes

An UV-Ozone reactor was developed with an ignition tube extracted into HID mercury lamp used to irradiation on zinc oxide (ZnO) and fluorinated tin oxide (FTO) films for PLEDs devices. Different exposures times were used. In contact angle measurements revealed better results for ZnO and FTO by 15 and 5 min, respectively. In Diffuse Reflectance Infra-red Fourier Transformed (DRIFT) spectroscopy allowed the observation of water, hydrocarbon and carbon dioxide adsorbed on the untreated TCO surfaces. After the UV-Ozone treatment the contaminants were significantly reduced or eliminated and the PLEDs devices decreased threshold voltages in comparison with respectively untreated TCOs.

Determinação de constituintes químicos em madeira de eucalipto por Pi-CG/EM e calibração multivariada: comparação entre redes neurais artificiais e máquinas de vetor suporte

Multivariate models were developed using Artificial Neural Network (ANN) and Least Square - Support Vector Machines (LS-SVM) for estimating lignin siringyl/guaiacyl ratio and the contents of cellulose, hemicelluloses and lignin in eucalyptus wood by pyrolysis associated to gaseous chromatography and mass spectrometry (Py-GC/MS). The results obtained by two calibration methods were in agreement with those of reference methods. However a comparison indicated that the LS-SVM model presented better predictive capacity for the cellulose and lignin contents, while the ANN model presented was more adequate for estimating the hemicelluloses content and lignin siringyl/guaiacyl ratio.

Determinação simultânea de ácido kójico e hidroquinona por espectrofotometria visível e calibração multivariada

A multivariate spectrophotometric method was developed for analysis of kojic acid/hydroquinone associations in skin whitening cosmetics. The method is based on the reaction between kojic acid and Fe3+ and on the reduction of Fe3+ by hydroquinone and further complexation of Fe2+ with 1,10-phenanthroline. The multivariate model was developed by Partial Least Squares Regression (PLSR), using 25 synthetic mixtures and mean-centered spectral data (350-380 nm). The use of 3 (kojic acid) and 2 (hydroquinone) latent variables permits the observation of mean errors of about 5% in the external validation phase.

Experimento didático de quimiometria para calibração multivariada na determinação de paracetamol em comprimidos comerciais utilizando espectroscopia no infravermelho próximo: um tutorial, parte II

The aim of this manuscript was to show the basic concepts and practical application of Partial Least Squares (PLS) as a tutorial, using the Matlab computing environment for beginners, undergraduate and graduate students. As a practical example, the determination of the drug paracetamol in commercial tablets using Near-Infrared (NIR) spectroscopy and Partial Least Squares (PLS) regression was shown, an experiment that has been successfully carried out at the Chemical Institute of Campinas State University for chemistry undergraduate course students to introduce the basic concepts of multivariate calibration in a practical way.

Influência de diferentes solventes utilizados na deposição de filme de poli(9-vinilcarbazol) em dispositivos OLEDs

This work studies the influence of the film deposition process on light emission performance and on threshold voltage of OLEDs, with architecture glass/ITO/PEDOT:PSS/PVK/Alq3/Al. The commercial PVK was dissolved in different solvents such as: chloroform, tetrahydrofuran, 1,2,4-trichlorobenzene and trimethylpentane. OLEDs were characterized by current-voltage and revealed a significant influence of the solvents, although all devices emitted green electroluminescence. A difference in threshold voltage up to 10 V was observed among OLEDs prepared from different solvents. The 1,2,4-trichlorobenzene showed best performance, presenting lowest treshold voltage (≈ 6 V), followed by tetrahydrofuran (≈ 8 V), trimethylpentane (≈ 14 V) and chloroform (≈ 16 V).

Máscaras mecânicas de sombra por eletrocorrosão para dispositivos eletro-ópticos

Shadow masks are used in manufacturing processes for electro-optic devices to transfer patterns with different shapes and dimensions. For fabrication of organic based devices, shadow masks should be made of materials stable against organic solvents, high temperature, and robust, remaining unchanged after multiple cycles of use and fixation. Thus, stainless steel is suitable for shadow masks. A simple, cheap and quick method of obtaining shadow masks by electrochemical corrosion of stainless steel is reported. The shadow mask was used to evaporate cathode material to obtain an organic light emitting diode with active area of 9 mm². This device exhibited a turn-on voltage of 5 V and luminance of 14 cd/m².

Avaliação de dispositivos de captura de imagens digitais para detecção colorimétrica em microzonas impressas

This report describes a study about the feasibility of using a conventional digital camera, a cell-phone camera, an optical microscope, and a scanner as digital image capture devices on printed microzones. An array containing nine circular zones was drawn using graphics software and printed onto transparency film by a laser printer. Due to its superior analytical performance, the scanner was chosen for the quantitative determination of Fe2+ in pharmaceutical samples. The data achieved using scanned images did not differ statistically from those attained by the reference spectrophotometric method at the confidence level of 0.05.

Experimento utilizando grãos para explorar a calibração em análises químicas

The conventional curriculum of Analytical Chemistry undergraduate courses emphasizes the introduction of techniques, methods and procedures used for instrumental analysis. All these concepts must be integrated into a sound conceptual framework to allow students to make appropriate decisions. Method calibration is one of the most critical parameters that has to be grasped since most analytical techniques depend on it for quantitative analysis. The conceptual understanding of calibration is not trivial for undergraduate students. External calibration is widely discussed during instrumental analysis courses. However, the understanding of the limitations of external calibration to correct some systematic errors is not directly derived from laboratory examples. The conceptual understanding of other calibration methods (standard addition, matrix matching, and internal standard) is imperative. The aim of this work is to present a simple experiment using grains (beans, corn and chickpeas) to explore different types of calibration methods.

DISPOSITIVOS DGT MODIFICADOS COM MATERIAIS ALTERNATIVOS PARA USO NA ESPECIAÇÃO DE ELEMENTOS TRAÇO

The use of MT-K10 Montmorillonite immobilized onto agarose was investigated in this work as an alternative binding phase in Diffusive Gradient in Thin Film (DGT) devices for the determination of metallic labile species. In addition, agarose itself was also used as the diffusive phase. The percentage of sorption of Zn2+, Cu2+, Cr3+, Mn2+, Cd2+, Pb2+, and Ni2+ onto the binding phase was higher than 80% and the desorption process for all elements was also greater than 75%. Elution factors were determined experimentally, ranging from 0.74 for Zn2+ and 0.90 for Cr3+ and Pb2+. The accumulation of all species was linear with time, in agreement with the Fick's 1st law of diffusion. The deployment of the alternative devices in natural waters was compared to commercial devices. Labile concentrations determined by the alternative devices were slightly superior compared to results obtained with the deployment of original DGT devices due to the less restrictive pores of agarose.

SISTEMAS ALTERNATIVOS DE CALIBRAÇÃO PARA DETERMINAÇÃO ESPECTROFOTOMÉTRICA SIMULTÂNEA DE ESPÉCIES COM INTERFERÊNCIA ESPECTRAL

Two simple and efficient procedures have been developed for the rapid simultaneous determination of compounds with mutual spectral interference (rifampicin (RIF) and isoniazid (INH)). The first method was based on the UV–Vis spectral signal (190–600 nm) of synthetic RIF and INH aqueous solutions, whereas the second method involved the visible spectral signal registered between 350 and 800 nm after the reaction of INH with a Cu2+/neocuproine complex. Both multivariate spectrophotometric methods show excellent prevision capacity, providing results that are statistically equivalent with those provided by the standard chromatographic procedure. The methods were validated according to criteria established by ANVISA, showing precision, accuracy and robustness compatible with the requirements for new analytical methods, additionally allowing the reduction of waste generation.