Valdomiro Lacerda Martins

Digital image-based flame emission spectrometry

A digital image-based flame emission spectrometric (DIB-FES) method for the quantitative chemical analysis is proposed here for the first time. The DIB-FES method employs a webcam to capture the digital images which are associated to a radiation emitted by the analyte into an air-butane flame. Since the detection by webcam is based on the RGB (red-green-blue) colour system, a novel mathematical model was developed in order to build DIB-FES analytical curves and estimate figures of merit for the proposed method. In this approach, each image is retrieved in the three R, G and B individual components and their values were used to define a position vector in RGB three-dimensional space. The norm of this vector is then adopted as the RGB-based value (analytical response) and it has revealed to be linearly related to the analyte concentration. The feasibility of the DIB-FES method is illustrated in three applications involving the determination of lithium, sodium and calcium in anti-depressive drug, physiological serum and water, respectively. In comparison with the traditional flame emission spectrometry (trad-FES), no statistic difference has been observed between the results by applying the paired t-test at the 95% confidence level. However, the DIB-FES method has offered the largest sensitivities and precision, as well as the smallest limits of detection and quantification for the three analytes. These advantageous characteristics are attributed to the trivariate nature of the detection by webcam.

Implementation of an automatic standard addition method in a flow–batch system: application to copper determination in an alcoholic beverage by atomic absorption spectrometry

A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow–batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow–batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaca”, available in Brazil. A SAM has been recommended for these analyses because “Cachacas” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow–batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n = 6) and 0.2 mg l −1 , respectively, for 1.0–7.0 mg l −1 Cu. By using five standard addition levels, the sample throughput was 70 h −1 and the consumption of sample and standard solution were 1.5 and 0.5 ml per

Flow-Batch Analyzer for the Chemiluminescence Determination of Catecholamines in Pharmaceutical Preparations

A novel, simple, cheap, flexible, versatile, and highly sensitivity flow-batch analyzer (FBA) with chemiluminescence detection was developed for determination of dopamine, norepinephrine, and epinephrine in pharmaceutical preparations. The method was based on the inhibitory effect of the mentioned catecholamines on a luminol-potassium hexacyanoferrate (III) chemiluminescence system in alkaline medium. The optimization of the chemical variables affecting this chemiluminescence inhibition effect has been carried out using a Box-Behnken experimental design. The sample throughput was 28 h−1. The system allowed the automatic preparation of standard solutions and analytical process can be accomplished just by changing the operational parameters in FBA control software.

A digital image-based method employing a spot-test for quantification of ethanol in drinks

A low-cost analytical method for quantification of ethanol in drinks based on the combination of a colorimetric spot-test and a digital image-based (DIB) method is proposed. The digital images from spot-test reactions were captured using a digital camera in a portable plastic chamber designed with internal lighting control. The images were decomposed by a RGB approach using freely available software. The R channel showed the best linearity, with two linear ethanol concentration ranges: from 1.0% to 20.0% v/v (r = 0.999) and from 25.0% to 50.0% v/v (r = 0.980), with limits of detection and quantification of 0.25% and 0.85% v/v, respectively, for the first analytical curve. The developed method was applied to quantification of ethanol in alcoholic drink samples with results in close agreement with those obtained using a spectrophotometric method at a confidence level of 95%, and with low waste generation (835 μL/spot-test). Thus, we believe that the DIB method can be useful with regard to environmental and social impacts, once the method has a low waste generation and uses an easily available instrumentation with potential for in situ determination during the alcoholic beverage production and its quality control.

An automatic flow-batch standard-addition method for sodium determination in alcohol fuel by flame photometry

The Brazilian Regulatory Agency for fuel production and commercialization requires that the sodium concentration in alcohol fuel should be determined by flame photometry and that the analytical curves should be obtained with matrix-matched standards. Notwithstanding, this methodology can produce inexact results because alcohol fuel presents a significant variability in matrix composition and, consequently, in the matrix effect. This problem can be circumvented by using the standard addition method (SAM). However, this method is slow and laborious when it carried out by manual procedures. To overcome these drawbacks, an automatic flow-batch SAM for sodium determination in alcohol fuel by flame photometry is described. This system requires only one standard solution, handles about 80 - 140 samples per hour and consumes a total volume of sample and of standard solution smaller than 1.5 mL for each analysis. The results present a standard deviation usually less than 0.1 mg L-1 (n = 4).

A digital image analysis method for quantification of sulfite in beverages

A novel, simple and low-cost analytical procedure for sulfite determination in beverage samples is presented. The approach proposed consists of image capture from a sulfite colorimetric reaction, using a system built with low-cost materials for luminosity control and digital image decomposition into the primary colors red (R), green (G) and blue (B). The colorimetric reaction is based on the reduction of Fe(III) to Fe(II) in the presence of sulfite and further reaction with o-phenanthroline to form the red complex [Fe(C12H8N2)3]2+. Under optimized reaction and system conditions, the analytical curve was linear in a sulfite concentration range of 8.0 to 140 mg L−1, with limits of detection and quantification of 2.6 mg L−1 and 8.0 mg L−1, respectively. The analytical method was applied to sulfite quantification in different beverage samples such as white wine, vinegar, rose wine, cashew juice and coconut water. The results acquired were in close agreement with those obtained using iodometric titration as a comparative method, with a confidence level of 95%. Moreover, the method can be useful with regard to social and environmental impacts, due to the low generated residues (800 μL per spot-test) and employs easily available instrumentation with the potential for in situ determination during the application of sulfites as additives during beverage production and quality control.

Wavelet-Based determination of Cu and Pb in water samples using potentiometric stripping analysis with a Lab-Made potentiostat

Este artigo demonstra a possibilidade de se realizar uma determinacao simultânea de chumbo e cobre em agua mineral, de rio e de torneira mediante analise por redissolucao potenciometrica empregando um potenciostato lab-made de baixo custo e um metodo de processamento de sinais baseado em wavelets. As concentracoes encontradas para Pb(II) e Cu(II) situaram-se na faixa 3-7 µg L -1 . Os desvios padrao relativos foram em media menores que 3%, o que e satisfatorio tendo em vista as baixas concentracoes dos analitos. Para comparacao, a determinacao foi tambem realizada empregando um equipamento comercial de alto padrao (µAutolab Type II, Eco Chemie). As medias e desvios padrao dos resultados foram similares aos obtidos com o potenciostato labmade. Nao foi verificada diferenca estatistica significativa de acordo com um teste t pareado ao nivel de confianca de 95%. This paper demonstrates the possibility of simultaneously determining lead and copper in mineral, river and tap water by potentiometric stripping analysis using a low-cost lab-made potentiostat and a wavelet-based signal processing method. Pb(II) and Cu(II) concentrations were found to be in the range 3-7 µg L -1 . Relative standard deviations were on average smaller than 3%, which is satisfactory in view of the trace concentration. For comparison, the determination was also carried out by using a high-end commercial equipment (µAutolab Type II, Eco Chemie). The average and standard deviation of the results were similar to those obtained with the labmade potentiostat. No significant statistical difference was verified according to a paired t-test at a confidence level of 95%.