Abstract: Optodes based on bromothymol blue (BB) and bromocresol purple (BP) acid-base indicators were constructed. The dyes were chemically immobilized on the surface of a bifurcated glass fiber optical bundle, which was previously silanised with 3-aminopropyl-triethoxysilane. A PTFE/acrylic cell was specially constructed, allowing the use of the optodes as detector in flow analysis systems. The optodes were evaluated for their pH responses in different flow approaches, such as continuous flow, flow injection and monosegmented flow systems. A steady state signal was achieved in the continuous flow system. The effect of the flow rate and the injected volume on the signal amplitude were studied. Signals up to 69 and 77% for BB optode and up to 82 and 92% for the BP optode of the steady state signal can be obtained by employing flow injection and monosegmented flow systems, respectively. The sampling frequency can be improved and sample consume can be lowered by employing the monosegment flow approach.

Abstract: An arrangement capable of implementing the four principal types of flow analysis processes, monosegmented flow analysis (MSFA), flow injection analysis with multicommutation and binary sampling (FIA-MBS), flow injection analysis with sandwich sampling (FIA-SS) and sequential injection analysis (SIA) is described. The core of the flow manifold is a six-way solenoid valve that is assembled together with three three-way solenoid valves in order to provide a versatile flow network. Software was written in VisualBasic 3.0 to give a friendly working structure allowing the user to easily choose the flow variables and the kind of flow system. The reliability of the flow set up for implementation of the four flow analysis systems was evaluated by means of the spectrophotometric determination of nickel in steel alloys, based on the formation of a colored complex with dimethylglyoxime (DMG). The performances of the four different flow methodologies were compared. The reagent consumptions per determination were 4.0 mg of triethanolamine, 6.0 mg of potassium persulfate and 0.6 mg of DMG. When the flow set up was instructed through the software to implement MSFA, FIA-MBS, and FIA-SS approaches, a sampling frequency of 40 samples/h was obtained, while 30 samples could be processed per hour in the SIA mode. The precisions, evaluated as the relative standard deviation of ten determinations were 0.7%, 1.6%, 1.8% and 3.1% for the MFSA, FIA-MBS, FIA-SS and SIA systems, respectively. The results for determination of nickel in steel alloys presented good agreement with the reference method (ICP OES), showing no significant difference at a confidence level of 95%. © 2005 Elsevier B.V. All rights reserved.

Abstract: A gravity flow-based manifold to perform turbidimetric determination of sulfate, comparing different approaches, such as sequential injection analysis (SIA), FIA with multicommutation and binary sampling (FIA-MBS), FIA with sandwich sampling (FIA-SS) and monosegmented flow analysis (MSFA) is described. Solutions of 5.0% barium chloride, 0.25 mol L-1 perchloric acid and 0.3% EDTA in 0.2 mol L-1 NaOH were used as precipitating agent, carrier fluid and cleaning solution, respectively. After optimization, SIA, FIA-MBS and FIA-SS approaches showed linear response ranges from 40 to 200 mg L-1, while for MSFA the range was from 20 to 125 mg L-1. In the SIA system, a sampling frequency of 30 samples per hour was obtained, while a value of 40 samples per hour was obtained when FIA-MSB, FIA-SS and MSFA approaches were employed. The flow manifold was evaluated by determining sulfate in plant, bovine liver and blood serum digests. The SIA, FIA-SS, FIA-MBS and MSFA systems showed a RSD of 3.2, 2.7, 2.0 and 1.0%, respectively, expressed as the relative standard solution. When the results were compared with deviation of the signal intensities of six measurements of a 120 mg L-1 SO42- solution. When the results were compared with those obtained by conventional FIA, no significant differences were observed for FIA-MSB, FIA-SS and MSFA at a confidence level of 95%, while for SIA the results were similar at a level of 97.5%.

Abstract: A flow approach for simultaneous multiple injection (SMI) in monosegmented flow anal. (MSFA) is described. In this approach, the sample and the reagent (or other solution, such as a diluting fluid) are simultaneously injected into the reaction coil of a monosegmented flow analyzer. The monosegment is homogenized while it is carried towards the detector. The sample dilution procedure is not based on a gradient concentration. pattern and dilution factors up to 150 were obtained by using hydrodynamic sampling. The system was applied to perform sample dilution in the determination of glucose in blood plasma. The results show good correlation with those obtained by the Clinical Hospital of UNICAMP. The SMI approach was also applied to add reagent to the sample in nitrite determination in natural water, providing a methodology that has a sampling frequency of 72/h, a relative standard deviation of <2%, at 60 µg/L N-NO2-, a linear response range up to 260 µg/L and a 2s limit of detection of 5 µg/L N-NO2-. Thus, the sensitivity is close to that of the manual reference method. Recovery tests carried out with sea water samples also showed that MSFA overcomes the Schlieren effect, without needing any special procedure.