Wellington da Silva Lyra

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.

A digital image-based method for determining of total acidity in red wines using acid–base titration without indicator

This work proposes the use of digital image-based method for determination of total acidity in red wines by means of acid-base titration without using an external indicator or any pre-treatment of the sample. Digital images present the colour of the emergent radiation which is complementary to the radiation absorbed by anthocyanines present in wines. Anthocyanines change colour depending on the pH of the medium, and from the variation of colour in the images obtained during titration, the end point can be localized with accuracy and precision. RGB-based values were employed to build titration curves, and end points were localized by second derivative curves. The official method recommends potentiometric titration with a NaOH standard solution, and sample dilution until the pH reaches 8.2-8.4. In order to illustrate the feasibility of the proposed method, titrations of ten red wines were carried out. Results were compared with the reference method, and no statistically significant difference was observed between the results by applying the paired t-test at the 95% confidence level. The proposed method yielded more precise results than the official method. This is due to the trivariate nature of the measurements (RGB), associated with digital images.

Indirect determination of sodium diclofenac, sodium dipyrone and calcium gluconate in injection drugs using digital image-based (webcam) flame emission spectrometric method

This paper proposes a digital image-based flame emission spectrometric (DIB-FES) method for indirect determination of sodium diclofenac, sodium dipyrone and calcium gluconate in injectable forms. The proposed DIB-FES method uses digital images obtained from a webcam, based on the RGB (Red-Green-Blue) system. It offers a simple and inexpensive way to quantify these organic substances using the radiation emitted by the alkaline and earth-alkaline metals present in their formulae. Analytical curves were constructed on the basis of the relationship between RGB values and calibration solution concentrations. The results showed no statistical difference between the proposed and reference methods when applying the paired t-test at a 95% confidence level. The proposed DIB-FES method also performed well in terms of the figures of merit LOD, LOQ, linear range, precision, and the accuracy as revealed by recovery tests.

Classificação periódica: um exemplo didático para ensinar análise de componentes principais

A dataset of chemical properties of the elements is used herein to introduce principal components analysis (PCA). The focus in this article is to verify the classification of the elements within the periodic table. The reclassification of the semimetals as metals or nonmetals emerges naturally from PCA and agrees with the current SBQ/IUPAC periodic table. Dataset construction, basic preprocessing, loading and score plots, and interpretation have been emphasized. This activity can be carried out even when students with distinct levels of formation are together in the same learning environment.

A portable, inexpensive and microcontrolled spectrophotometer based on white LED as light source and CD media as diffraction grid.

A portable, microcontrolled and low-cost spectrophotometer (MLCS) is proposed. The instrument combines the use of a compact disc (CD) media as diffraction grid and white light-emitting diode (LED) as radiation source. Moreover, it employs a phototransistor with spectral sensitivity in visible region as phototransductor, as well as a programmable interrupt controller (PIC) microcontroller as control unit. The proposed instrument was successfully applied to determination of food colorants (tartrazine, sunset yellow, brilliant blue and allura red) in five synthetics samples and Fe(2+) in six samples of restorative oral solutions. For comparison purpose, two commercial spectrophotometers (HP and Micronal) were employed. The application of the t-paired test at the 95% confidence level revealed that there are not significant differences between the concentration values estimated by the three instruments. Furthermore, a good precision in the analyte concentrations was obtained by using MLCS. The overall relative standard deviation (R.S.D.) of each analyte was smaller than 1.0%. Therefore, the proposed instrument offers an economically viable alternative for spectrophotometric chemical analysis in small routine, research and/or teaching laboratories, because its components are inexpensive and of easy acquisition.

Biamperometric Determination of Tetracycline in Pharmaceuticals

Abstract A fast, reliable, and low cost biamperometric flow‐injection method, with an error of 1.3% and an analytical throughput of 55 samples h−1, for determination of tetracycline hydrochloride in pharmaceuticals capsules is proposed. The analytical curve was linear (r=0.998) in the range 10 to 50 mg l−1 using Fe(CN)6 3− and NaOH solutions as reagent and carrier stream/supporting electrolyte, respectively. A relative standard deviation of 1.6% (10 sequential injections of 30.0 mg l−1) was verified with detection and quantification limits of 0.6 and 3.4 mg l−1, respectively.

Flow Injection Determination of Metronidazole through Spectrophotometric Measurement of the Nitrite Ion Produced upon Alkaline Hydrolysis

A new method for metronidazole determination, based on spectrometric monitoring of a diazonium salt produced in-line by alkaline hydrolysis released nitrite ions, was developed and successfully applied to pharmaceutical tablets (r = 0.9993, 2.0-20.0 mg L-1, DL = 0.7 mg L-1) with no interference from common ingredients accompanying the drug.

Um fotômetro multi-led microcontrolado, portátil e de baixo custo

A microcontrolled, portable and inexpensive photometer is described. It uses six light-emitting diodes (LEDs) as radiation sources and a phototransistor as detector, as well as a microcontroller (PIC - Programmable Controller of Interruption). This device provided total autonomy to the proposed photometer, which was successfully applied to determination of Fe2+ in ferrous syrups and of seven clinical biochemical parameters. As the components are cheap (~U

Versatilidade de um sistema em fluxo multicomutado na determinação espectrofotométrica de três analitos

30.00) and easy to find, the proposed photometer is an economical alternative for routine chemical analyses in small laboratories, for research and teaching. Being portable and microcontrolled, it allows doing field chemical analyses.

Digital image-based titrations

In this work was developed a multicommuted flow system for determination of sodium diclofenac, acetylsalicylic acid and fluoride ions in ampoules, tablets and tap waters, respectively. For sodium diclofenac the method used was based on its reaction with potassium permanganate (20 80 mg L 1 ). For acetylsali yli a id the ethod used as ased o Tri der s rea tio after alkali e hydrolysis of the analyte (25 100 mg L -1 ). For fluoride ions the method used was the well-known SPADNS (0.4 1.6 mg L -1 ). Results were compared with their respective reference methods and, by applying the paired t-test, no statistic difference between them was verified at the 95% confidence level. After optimization of the variables of the analytical system, it was able to analyze 80, 72 and 68 sample h 1 containing sodium diclofenac, acetylsalicylic acid and fluoride, respectively with reduced waste generation according to basic principles of green chemistry.Neste trabalho foi desenvolvido um sistema de multicimutacao em fluxo para determinacao de diclofenaco de sodio, acido acetilsalicilico e fluoretos em injetaveis, comprimidos e aguas de torneira, respectivamente. Para diclofenaco de sodio o metodo usado foi baseado em sua reacao com permanganato de potassio (20 - 80 mg L -1 ). Para acido acetilsalicilico o metodo usado foi baseado na reacao de Trinder apos hidrolise alcalina do analito (25 - 100 mg L -1 ). Para ions fluoreto o metodo usado foi o bem conhecido SPADNS (0.4 - 1.6 mg L -1 ). Resultados foram comparados com seus respectivos metodos de referencia e, aplicando o teste- t emparelhado, nenhuma diferenca estatisticamente significativa foi verificada entre eles ao nivel de confianca de 95%. Apos a otimizacao das variaveis do sistema analitico, ele foi capaz de analizar 80, 72 e 68 amostras h -1 contendo diclofenaco de sodio, acido acetilsalicilico e fluoretos, respectivamente com geracao de residuos reduzida de acordo com os principios basicos da quimica verde.