Abstract: A monosegmented flow system was employed for the determination of low contents of phosphate in natural water. In this approach, sample and reagents are simultaneously injected to a PTFE reaction coil where the homogenization of the mixture occurs while the monosegment is pumped forwards the photometric detector. The proposed system was evaluated by determining phosphate ion, based on the reaction of association between molybdophosphate and malachite green. It was evaluated individually the best concentration of the reagent solution in relation to blank signal (absorbance of the blank) and the sensitivity of the method. A factorial design was proposed to explain the contribution of each component on the formation of the ion association complex, evaluating the individual contributions as well as the synergistic and antagonistic effects. With the established conditions, phosphorous is determined in the concentration range of 5.0-75 µg P PO43- L-1 (r=0.9992), with a detection limit of 0.70 µg P PO43- L-1 and a relative standard deviation of 2% (20 µg P PO43- l-1, n=8). The proposed method has a sampling frequency of 72 h-1.

Abstract: A versatile potentiometer that works with electrode arrays inflow injection and/or monosegmented flow systems is described. The potentiometer is controlled by a microcomputer that allows individual, sequential multiplexed or random accesses to eight electrodes while employing only one reference electrode. The instrument was demonstrated by monitoring an array of seven flow-through ion-selective electrodes for Ag+ and for three electrodes for Cl-, Ca2+ and K+. The figures of merit of the individual and multiplexed (summed) readings of the electrode array were compared. The absolute standard deviation of the measurements made by summing the potential of two or more electrodes was maintained constant, thus improving the precision of the measurements. This result shows that an attempt to combine the signals of the electrodes to produce a more intense signal in the Hadamard strategy is feasible and accompanied by a proportional improvement in the precision of individual measurements. The preliminary tests suggest that the system can allow for 270 determinations per hour, with a linear range from 1.0 x 10^-2 to 1.0 x 10^-4 mol L-1 for the three different analytes. Detection limits were estimated as 3.1 x 10^-5, 3.0 x 10^-6 and 1.0 x 10^-5 mol L-1 for Cl-, Ca2+ and K+, respectively.

Abstract: An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 µl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2'-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 µg L-1 (r = 0.9995) with a relative standard deviation of 2% (200 µg l-1, n = 5) and a detection limit of 20 µg l-1. The analytical curve was linear over the concentration range 25-500 µg L-1 (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 µg L-1 and the relative standard deviation was 6% (50 µg l-1, n = 5).