Ana Cristi Basile Dias

Multi-pumping flow systems (MP) utilize solenoid pumps as fluid propelling devices, which deliver pulsed flows. This feature was evaluated in relation to the design, operation and performance of the system, to the mixing conditions, and to the dispersion of the introduced solution. The general evaluation of the MP systems involved investigations about precision and accuracy of the pulse volumes, as well as the pump ruggedness. To this end, gravimetric measurements were carried out. Moreover, dispersion was evaluated by exploiting a colored solution and spectrophotometric monitoring. Results were corroborated through analytical applications. Use pumps delivering higher pulse volumes (>25 l) was limited when the pulsation frequency was >4.0 Hz. The experimentally measured volumes were in agreement with to the expected values (relative error <2.0 %). Sample dispersion was lower in relation to that inherent to laminar flow (multi-commuted flow system, MC).Exploitation of pulsed flow led to a enhanced reaction development mainly due to shaking of neighboring fluid elements. This aspect was important in relation to spectrophotometric determination of bromhexine in pharmaceuticals The method was based on electrophylic coupling of bromhexine with 3-methyl-2-benzothiazolinone hydrazone (MBTH), with further oxidation by Ce(IV) under acidic medium. Analytical sensitivity was fair, reagent consumption was low and sampling rate was 300 h-1. These figures of merit were not compared with those inherent to the MC system due to the lack of sensitivity of this system. Another application was the spectrophotometric determination of phosphate in soil extracts relying the molybdenum blue formation. Best analytical results were obtained for <0.5 Hz pulse frequency, due to the higher available time for interaction among the involved chemical species. The proposed MP system required lower sample volume (48 l) in relation to the MC system (96 l), being characterized by higher sampling rate (MP: 144 h-1; MC: 67 h-1). Analytical results related to soil extracts were in agreement between them and with the reference method. Visualization of a dispersing sample in a pulsed flow became feasible using the laser induced fluorescence technique applied to Rhodamine B, RB. Experiments were performed under high (3.0 Hz) or low (0.5 Hz) pulse frequency, optional insertion of a reactor between the injection point and detection, and vertical or horizontal positioning of the flow-cell. Analyses of the graphs obtained allowed the visualization of the mass re-distribution in function of time. In general, vortex formation at the central portion of the sample zone and a high RB migration in the radial direction, were noted. Concerning axial direction, better sample / carrier stream interactions were observed for lower pulse frequency and insertion of the 60-cm reactor. Vortex establishment led to a punctual and fast mixing, as confirmed by the analytical applications

"Sistemas de análises químicas em fluxo explorando multi-impulsão e detecção espectrofotométrica: aplicação a formulações farmacêuticas e a extratos de solos" / Multi-pumping flow systems with spectrophotometric detection: application to analysis of pharmaceuticals and soil extracts

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