Um espectrofotômetro de emissão em chama portátil empregando um nebulizador ultrassônico de rede ativa e detecção por imagens digitais

Abstract

Commercial flame photometers are still widely used for the determination of sodium, lithium, potassium, and calcium, mostly due to their low acquisition and maintenance costs. However, these instruments are not portable in view of their significant mass and dimensions, for they require a stable power supply and also a fixed gas storage and transportation system. Thus, it is proposed the development of a portable flame spectrophotometer composed of: (1) an active mesh ultrasonic nebulizer (≈ 110 kHz); (2) a portable torch as the burner; (3) a gas tank; (4) a transmissive diffraction grid (1000 lines mm-1); and (5) an Android smartphone or a charge-coupled device (CCD) spectrometer as the detector. The Android application, named SmartFES, uses captured images from device’s camera to acquire the emission spectra in real time. The pulsed nebulizer system was designed to insert sample volumes as low as 5 μL into a nebulizer chamber printed on polylactic acid (PLA) using a 3D printer (RepRap). Other parts of the instrument were also printed in both PLA and acrylonitrile-butadienestyrene (ABS). The analyses can be performed 5 min after the ignition of the flame, which remains stable for up to 9.4 h. Analytical curves with linear ranges for sodium (3 – 10 mg L−1), lithium (1 – 10 mg L−1) and calcium (200 – 800 mg L−1) were obtained and their analytical performance were evaluated by estimating the limit of detection (LOD), limit of quantification (LOQ), and sensibility. The portable spectrophotometer was applied to the determination of sodium in a certified fresh water sample using the smartphone and the commercial spectrometer as detectors, obtaining relative standard deviations of 2.0% and 2.3% and relative errors of −2.1% and −3.9%, respectively. Lithium was also quantified in antidepressant tablets using the CCD spectrometer, obtaining relative standard deviations of between 1.4% and 3.0%. These results demonstrate that the portable flame spectrophotometer can be used to analyze real samples in a simple, fast and inexpensive way, with low waste generation.