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A method for the screening of biogenic amines in waters, whose presence at some concentration levels potentially cause adverse effects on humans, was developed for the first time. A suitable and easy to operate system, with low reagent consumption was devised. The proposed flow-based system was divided into two analytical parts, preconcentration and derivatization of the biogenic amines. Solid phase extraction, using a Chelex 100 resin, was the newly chosen strategy for preconcentration of the analyte and also removal of possible matrix interferences. Fluorescamine was used as derivatization reagent for biogenic amines followed by fluorimetric detection. The influence of different sorbent materials for preconcentration and flow system parameters such as pH of standards and buffer, composition of the eluent solution, flow-rates, standard/sample volume, were studied. The interference of ammonia was assessed, and no interference was observed. The limits of detection and quantification were 1.7 and 5.6 µmol L−1, respectively. The developed system was applied to water samples and the recovery results were 98 ± 7%.

A solid phase extraction flow injection system for the spectrophotometric determination of total zinc in plant digests was developed. Solid phase extraction was chosen as a strategy for zinc preconcentration and removal of some interferences. The determination of zinc was based on the colorimetric reaction with Zincon. As detection system, a multi-reflection flow cell coupled with a light emitting diode was used. The analytical characteristics of the methodology such as pH of standard/sample solution, nitric acid concentration, the placement of SPE column within the manifold and preconcentration flow rate were studied. The interference of some metals present in plants was also assessed. The limits of detection and quantification achieved were 0.04 mg L − 1 and 0.12 mg L − 1 , respectively. The corresponding Zincon consumption was 0.17 mg for each determination. The developed system was applied to plant digests and the results obtained were in agreement with those obtained with reference procedure.

The objective of this work was to make a contribution to study the potential of the sequential injection-lab-on-valve (SI-LOV) format for the miniaturization of enzymatic assays, by using different measurement modes (peak height and initialrate-based measurement). A LOV system was developed for the enzymatic assay of ethanol in beverages, based on the conversion of ethanol to acetaldehyde by alcohol dehydrogenase, using spectrophotometric detection. The use of the kinetic-based approach permits the applicability of the enzymatic determination to samples with intrinsic absorption, with a higher determination throughput. A linear dynamic application range up to 0.040% (v/v) was achieved for both initial rate and for the peak height measurement, with good repeatability (R.S.D. < 5.0% and +, buffer and sample consumption per assay were 0.12 U, 0.066 mg, 150 and 15 μL, respectively. The determination rate achieved was 37 and 27 determinations h-1 for the initial rate and for the peak height measurement, respectively. The results obtained for several alcoholic beverages, including a certified sample material, were not statistically different from those obtained by the reference procedures.

This work exploits a multisyringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0mpathlength, 550mmi.d. and 250mL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2mg L−1, for copper and zinc, respectively), without the need for any preconcentration step. The system also provided a linear response up to 100mg L−1 with a high throughput (43 h−1) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.

We developed a sequential injection analysis (SIA) method for the determination of iron in coastal, ground, and surface fresh waters using two different reagents (ferrozine and 1,10-phenathroline). The methodology uses a double-line SIA system to improve mixing conditions between sample and reagent solutions. A liquid waveguide capillary cell (LWCC) with 1.0 m pathlength, 550 μm i.d., and 250 μL internal volume was used to enhance the sensitivity of the determination. The detection limits for the ferrozine and 1,10-phenanthroline reagent were 0.15 and 0.35 μg L–1, respectively. The system provides a linear response up to 20 μg L–1 and has a high throughput rate (41 h–1), low reagent consumption, and also low effluent production for both reagents. The developed method was applied to natural waters (river, well, ground, potable, and sea waters) and one reference water sample.

Two analytical methods were proposed for the determination of sodium chloride. A flow injection turbidimetric determination, based on the precipitation of silver chloride, was found to be a simple methodology to be implemented for routine analysis with a high sampling frequency, low reagent consumption and waste production in comparison with the reference methodology. On the other hand, the infrared methodology allowed NaCl determination with no reagent consumption. Both methodologies can be implemented for routine chemical analysis determinations in the food industry.

Submitted by Teresa Monteiro (tlago@porto.ucp.pt) on 2011-10-18T10:19:54Z No. of bitstreams: 1 trab-nac_2008_ESB_1022_Rangel_António_38.pdf: 605524 bytes, checksum: c5e402564ca228c15f628093c4c4a824 (MD5) Made available in DSpace on 2011-10-18T13:21:55Z (GMT). No. of bitstreams: 1 trab-nac_2008_ESB_1022_Rangel_António_38.pdf: 605524 bytes, checksum: c5e402564ca228c15f628093c4c4a824 (MD5) Previous issue date: 2009

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