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.

In this work an unmanned aerial vehicle (UAV) was adapted to be used as an environmental tool to collect water samples of sea, estuary, and mangrove for further analysis by gas chromatography with a mass detector (GC-MS). The sampling automated system was based on a microcontroller, a solenoid valve, and a peristaltic mini-pump that was coupled to a quadcopter UAV. The apparatus was properly calibrated to acquire 100 mL of environmental water at 4.6 min. After, the concentration of BTEX (benzene, toluene, ethylbenzene, and o, m, p-xylenes) was analyzed in laboratory using GC-MS and the BTEX concentration ranged from 0.3 to 5.0 µg L-1 with a recovery from 83.9 to 118% with a relative standard deviation lower than 7.0%. Tests of cross-contamination were performed by simultaneous sampling and laboratory blank was carried out and no contamination was found for BTEX analysis. Based on the results, the adapted UAV presented a very useful ability to collect samples in difficult access areas such as mangroves, points between rocks, corals reefs, without health risk and without impacting the fragile ecosystem being an interesting tool for environmental purposes.

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.