This work describes the analysis of molecular spectroscopy in the UV/Vis region, as well as the study of transmittance, absorption, and reflectance phenomena in an undergraduate class using an LED (light emitting diodes)-photometer and digital image-based (DIB) method using a smartphone to compare with a benchtop spectrophotometer and literature data employing paired T-test for 95% confidence. The novelties of this work are focused on the use of simple, low-cost, and portable analytical instrumentation, based on an RGB-LED photometer and DIB using a smartphone, for teaching Chemistry to undergraduate classes. Moreover, discussions were held on concepts related to the Beer-Lambert law, spectroscopy, pH, equilibrium shift, and calculation for determining the equilibrium constant and pKa of bromothymol blue, which was used as proof of concept. The advantages are the use of low-cost instrumentation for teaching Chemistry, students’ access to concepts, such as radiation source, photodetector, transmittance calculation from analog data, regulation of the power of the light emitted by the LED, and details to understand the interaction between matter and light were described by undergraduate students in Physics and Chemistry throughout the course of Experiments in Thermodynamic and Chemical Equilibrium. The better understanding of theoretical concepts and the possibility of taking the RGB-LED-photometer and DIB instrumentation to schools, exhibitions, science fairs, and Chemistry teaching meetings were pointed out by students as the main advantages of the instrumentation and methods described.

Neste trabalho, a aplicação de um microssistema analítico construído com tecnologia LTCC (cerâmica cossinterizada a baixa temperatura) com incorporação monolítica de uma cela óptica de fluxo para determinação de dipirona em formulações farmacêuticas é descrita. O sistema de detecção baseou-se na formação de um cromóforo azul entre a dipirona e Fe(III) monitorado fotometricamente em 630 nm usando um minifotômetro de LED lab-made construído com um diodo emissor de luz como fonte de radiação e um fotodiodo de Si como detector. O minifotômetro elaborado apresentou um bom desempenho com respeito à elevada relação sinal ruído, baixo ruído e sensibilidade satisfatória. A curva analítica foi linear na região de concentração de dipirona de 1,0 × 10-4 a 3,5 × 10-3 mol L-1 tendo sido obtido um limite de detecção de 4,5 × 10-5 mol L-1 e um tempo total de análise de 20 s equivalente à uma frequência analítica de 195 h-1 com pouca geração de resíduos por análise (480 µL).

In this work, an analytical microsystem based on LTCC (low-temperature co-fired ceramic) technology with monolithic incorporation of an optical flow cell for determination of dipyrone in pharmaceuticals is described. The detection system is based on the formation of a blue chromophore between dipyrone and Fe(III) photometrically monitored at 630 nm using a lab-made LED mini-photometer constructed with a light emitting diode as a radiation source and a Si photodiode as a detector. The lab-made mini-photometer elaborated presented a good performance in regard to high signal/noise ratio, low drift and good sensitivity. The analytical curve was linear in the dipyrone concentration range from 1.0 × 10-4 to 3.5 × 10-3 mol L-1, limit of detection of 4.5 × 10-5 mol L-1 and total time of analyses of 20 s yielding an analytical frequency of 195 h-1 with a low waste generation per analysis (480 µL).

This study reports on the construction of a turbidimeter employing light emitting diodes as radiation source at a wavelength of 405 nm, a photodiode as detector, a temperature sensor and a microcontroller used for data acquisition and processing. The turbidimeter was applied to determine sulfate concentrations in natural water employing barium chloride as reagent. Potential interferences and recovery studies were performed and an interference of 3.5 % and a recovery between 97.8 and 108 % were estimated. The analytical performance of in situ turbidimeter for the determination of sulfate was evaluated and compared with two commercial spectrophotometers and a good agreement was obtained.

A análise turbidimétrica e nefelométrica sequencial (STN) para duas aplicações analíticas empregando um nefelômetro e turbidímetro microcontrolado portátil (PMTN) é proposta. O PMTN é constituído de diodos emissores de luz, fotodiodos, microcontrolador como unidade de processamento central (CPU) e um um LCD (liquid crystal display) como amostrador. Os métodos STN foram aplicados para a determinação de N-acetilcisteína em formulações farmacêuticas nos intervalos de concentração de 8,0 × 10-5 a 5,0 × 10-3 mol L-1 (nefelometria) e de 5,0 × 10-5 a 1,2 × 10-3 mol L-1 (turbidimetria) com limites de detecção (LOD) de 2.6 × 10-6 e 7,5 × 10-6 mol L-1, respectivamente. As análises STN também foram executadas para a determinação de tiamina na faixa de concentração de 5,0 × 10-6 a 2,5 × 10-4 mol L-1 e de 5,0 × 10-6 a 1,0 × 10-4 mol L-1 com LOD de 5,91 × 10-8 e 3,11 × 10-8 mol L-1 respectivamente no modo nefelométrico e turbidimétrico.

Sequential turbidimetric and nephelometric (STN) analysis for two distinct analytical applications employing a portable microcontrolled turbidimeter and nephelometer (PMTN) is proposed. The PMTN is based on light emitting diodes, photodiodes and, a microcontroller as a central processing unit with a LCD (liquid crystal display) as displayer. The STN methods were applied to determine N-acetylcysteine and two analytical curves in the concentration ranges from 8.0 × 10-5 to 5.0 × 10-3 mol L-1 and from 5.0 × 10-5 to 1.2 × 10-3 mol L-1 were obtained to nephelometry and turbidimetry, respectively. Limits of detection (LOD) of 2.6 × 10-6 and 7.5 × 10-6 mol L-1 were acquired for these procedures. The STN analyses were also performed to determinate thiamine and two analytical curves in the concentration ranges from 5.0 × 10-6 to 2.5 × 10-4 mol L-1 and from 5.0 × 10-6 to 1.0 × 10-4 mol L-1 with LOD of 5.91 × 10-8 and 3.11 × 10-8 mol L-1 were acquired for nephelometry and turbidimetry, respectively.

Um nefelômetro microcontrolado portátil e de baixo custo é proposto para a determinação de potássio em água de coco e bebidas energéticas. O nefelômetro foi construído utilizando dois LEDs (diodos emissores de luz) como fontes de radiação em 465 nm e 880 nm, dois fotodiodos como fotodetectores e um controlador de interface periférica (PIC) para aquisição e processamento dos dados. O nefelômetro foi utilizado para determinar íons potássio pelo monitoramento do precipitado formado na reação entre íons K+ e tetrafenilborato em meio básico na presença de álcool polivinílico. A curva analítica foi linear para potássio na faixa de concentração de 5,0×10"6 a 5,0×10"4 mol L"1, com um limite de detecção de 4,0×10"7 mol L"1. Um desvio padrão relativo de 0,2 % para uma solução de potássio 1,6×10"4 mol L"1 (n = 10) foi obtido. Respostas rápidas e confiáveis e baixo consumo de energia são outras características do nefelômetro proposto.

A low-cost portable microcontrolled nephelometer for the determination of potassium in coconut water and energy beverages is proposed. The nephelometer was constructed using two LEDs (light emitting diodes) as radiation sources at 465 nm and 880 nm, two photodiodes as photodetectors, and a peripheral interface controller (PIC) to acquisition and processing data of the nephelometer. The nephelometer was used to determine potassium ions by monitoring the precipitate formed from the reaction between K+ and tetraphenylborate anion in a basic medium in the presence of polyvinyl alcohol. The analytical curve was linear in the potassium concentration range from 5.0×10"6 to 5.0×10"4 mol L"1, with a limit of detection of 4.0×10"7 mol L"1. A relative standard deviation of 0.2 % for 1.6 × 10"4 mol L"1 potassium solution (n = 10) was obtained. Fast and reliable responses, low power consumption are other attractive features of the proposed nephelometer.

Um procedimento de análise por injeção em fluxo turbidimétrico simples, exato e preciso é descrito para determinação de acetilcisteína em formulações farmacêuticas. O procedimento é baseado na precipitação da acetilcisteína com solução de nitrato de prata em meio ácido e o sal insolúvel produzido foi monitorado em 410 nm. A curva analítica para a acetilcisteína foi linear no intervalo de concentração de 1,0 × 10-4 a 1,0 × 10-3 mol L-1 com um limite de detecção de 5,0 × 10-5 mol L-1. A freqüência de amostragem foi de 60 h-1 e os desvios padrões relativos (RSD) foram menores do que 2,0 % para soluções de acetilcisteína de 1,0 × 10-4 e 5,0 × 10-4 mol L-1 (n=10). A recuperação deste analito em quatro amostras variou de 97,6 a 103%. O test-t pareado mostrou que os resultados obtidos para acetilcisteína em produtos farmacêuticos usando o procedimento em fluxo proposto e o método oficial, foram concordantes em um nível de confiança de 95%.

A simple, accurate and precise flow-injection turbidimetric procedure is reported for the determination of acetylcysteine in pharmaceutical formulations. The procedure is based on the precipitation of acetylcysteine with silver nitrate solution in acid medium and the insoluble salt produced was monitored at 410 nm. The analytical curve for acetylcysteine was linear in the concentration range from 1.0 × 10-4 to 1.0 × 10-3 mol L-1 with a detection limit of 5.0 × 10-5 mol L-1. The sampling rate was 60 h-1 and the relative standard deviations (RSDs) were less than 2.0% for 1.0 × 10-4 and 5.0 × 10-4 mol L-1 acetylcysteine solutions (n=10). The recovery of this analyte in four samples ranged from 97.6 to 103 %. A paired t-test showed that all results obtained for acetylcysteine in pharmaceutical products using the proposed flow-injection procedure and the official procedure agreed at the 95% confidence level.

Um procedimento de análise por injeção em fluxo espectrofotométrico simples, exato e preciso é descrito para determinação de captopril em formulações farmacêuticas. Nesse procedimento o captopril é oxidado pelo Fe(III) produzindo Fe(II) que foi espectrofotometricamente monitorado como complexo Fe(II)-1,10-fenantrolina em 540 nm. A curva analítica para o captopril foi linear no intervalo de concentração de 1,0 × 10-5 a 8,0 × 10-4 mol L-1 com um limite de detecção de 5,0 × 10-6 mol L-1. A recuperação deste analito em cinco amostras variou de 98,5 a 102,4%. A freqüência de amostragem foi de 60 h-1 e o desvio padrão relativo (RSD) foi menor do que 0,2% para uma solução de captopril 4,0 × 10-4 mol L-1 (n=10). O test-t pareado mostrou que os resultados obtidos para o captopril em produtos farmacêuticos, usando o procedimento em fluxo proposto e o método potenciométrico, foram concordantes em um nível de confiança de 95%.

A simple, accurate and precise flow-injection spectrophotometric procedure is reported for the determination of captopril in pharmaceutical formulations. In this procedure, captopril was oxidized by iron(III) and the iron(II) produced was spectrophotometrically monitored as iron(II)-1,10-phenantroline complex at 540 nm. The analytical curve for captopril was linear in the concentration range from 1.0 × 10-5 to 8.0 × 10-4 mol L-1 with a detection limit of 5.0 × 10-6 mol L-1. The recovery of this analyte in five samples ranged from 98.5 to 102.4%. The analytical frequency was sixty determinations per hour and the RSD was less than 0.2% for a captopril concentration of 4.0 × 10-4 mol L-1 (n = 10). A paired t-test showed that all results obtained for captopril in commercial formulations using the proposed flow injection procedure and a potentiometric procedure agreed at the 95% confidence level.