Desenvolvimento de instrumentos e procedimentos analíticos automáticos com detecção quimiluminescente e espectrofotométrica.
Abstract
In the present work is described computer-controlled flow systems
designed for process control of L-alanine synthesis and for bromide
determination in this amino acid, presented as a contaminant species. Since the
analytical systems were computer controlled, all the procedures steps, such as,
stopped flow, dilution, pH adjustment, analyte concentration and sample clean
up, were performed without operator assistance. In order to carry out
chemiluminescent reaction, a simple and low cost device (ca. US$ 150) that
comprises two photodiodes fixed in lab-made Perspex flow cell was proposed.
Regarding L-alanina determination, it was exploited the L-amino acid oxidize
enzyme reaction. In this system, the sample was injected into a carrier stream,
passing through a column packed with this immobilized enzyme. The product of
the amino acid oxidation, hydrogen peroxide, was determined by the
chemiluminescent reaction with luminol. The interfering species of the
enzymatic reaction was suppressed by coupling in the flow system a column
packed with a strong anionic resin. A linear concentration range between 0.5 and
25 mmol L-1 and a 0.08 mmol L-1limit of detection were some of the analytical
characteristics of this system. Regarding the chemiluminescent bromide
determination, the procedure was based on bromide oxidation by chloramine-T
followed by the reaction of the formed bromine with luminol. In order to
minimize the interference of alanina in the chemiluminescent reaction, a column
packed with a strong anionic resin was used for analyte concentration and
sample clean up. The analytical features obtained were a linear range between
0.010 and 1.000 mg L-1 (r=0.999) and a limit of detection of 1 µg L-1 of Br-.
Also in this work is reported the development and the characterization of a lowcost
device for NO2 determination in atmosphere exploiting the Griess-Slatzman
reaction. The NO2 was sampled from the atmosphere by a porous membrane
tube, which was also used as flow cell. To monitor the colored-forming reaction,
it was constructed a dual-wavelength LED-based spectrophotometer. With the
proposed device it was obtained a 0.5 ppbv limit of detection of NO2, a low
reagent consumption (100 µL per determination), 5 % relative standard
deviation for 5 ppbv NO2 sample concentration and long term stability, at least
168 hours without requiring calibration procedure.