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In this work, the design of a microfluidic paper-based analytical device (μPAD) for the quantification of nitrate in urine samples was described. Nitrate monitoring is highly relevant due to its association to some diseases and health conditions. The nitrate determination was achieved by combining the selectivity of the nitrate reductase enzymatic reaction with the colorimetric detection of nitrite by the well-known Griess reagent. For the optimization of the nitrate determination μPAD, several variables associated with the design and construction of the device were studied. Furthermore, the interference of the urine matrix was evaluated, and stability studies were performed, under different conditions. The developed μPAD enabled us to obtain a limit of detection of 0.04 mM, a limit of quantification of 0.14 mM and a dynamic concentration range of 0.14–1.0 mM. The designed μPAD proved to be stable for 24 h when stored at room temperature in air or vacuum atmosphere, and 60 days when stored in vacuum at −20 °C. The accuracy of the nitrate μPAD measurements was confirmed by analyzing four certified samples (prepared in synthetic urine) and performing recovery studies using urine samples.

A spectrophotometric flow-based method for the determination of nickel in recreational waters is proposed. In this scenario, the strategy was to devise a miniaturized and automatic system based on sequential injection analysis, aiming for an expeditious, real-time and low-cost determination. For the spectrophotometric determination, dimethylglyoxime was used as color reagent due to its selectivity for nickel. Considering the expected low concentration and low sensitivity of the coloured reaction, a long pathlength flow cell was used to increase the sensitivity. The potential interference of metal ions commonly present in freshwaters was assessed and no significant differences ( < 10%) were observed, except for manganese. This interference was overcome by adding manganese to the reagent, thus acting as a fixed interference strategy. The limit of detection and quantification were 6.3 and 21.1 µg L−1, respectively. The method was applied to the quantification of nickel in certified water samples and the results were in agreement with the certified values. Additionally, the method was successfully applied to the quantification of nickel in spiked freshwaters and the results were in agreement with those obtained with the reference method.

In this work, a flow-based spectrofluorimetric method for iodine determination was developed. The system consisted of a miniaturized chip-based flow manifold for solutions handling and with integrated spectrofluorimetric detection. A multi-syringe module was used as a liquid driver. Iodide was quantified from its catalytic effect on the redox reaction between Ce(IV) and As(III), based on the Sandell–Kolthoff reaction. The method was applied for the determination of iodine in salt, pharmaceuticals, supplement pills, and seaweed samples without off-line pre-treatment. An in-line oxidation process, aided by UV radiation, was implemented to analyse some samples (supplement pills and seaweed samples) to eliminate interferences and release iodine from organo-iodine compounds. This feature, combined with the fluorometric reaction, makes this method simpler, faster, and more sensitive than the classic approach of the Sandell–Kolthoff reaction. The method allowed iodine to be determined within a range of 0.20–4.0 µmol L−1, with or without the in-line UV digestion, with a limit of detection of 0.028 µmol L−1 and 0.025 µmol L−1, respectively.

The development of fast, automatic and less expensive methods of analysis has always been the main aim of flow methodologies. The search for new procedures that still maintain the reliability and accuracy of the reference procedures is an ever growing challenge. New requirements are continually added to analytical methodologies, such as lower consumption of samples and reagents, miniaturisation and portability of the equipment, computer interfaces for full decision systems and so on. Therefore, the development of flow methodologies meeting the extra requirements of water analysis is a challenging work. Sequential injection analysis (SIA) presents a set of characteristics that make it highly suitable for water analysis. With sequential injection analysis, most routine determinations in waters can be performed more quickly with much lower reagent consumption when compared to reference procedures. Additionally, SIA can be a valuable tool for analyte speciation and multiparametric analysis. This paper critically reviews the overall work in this area.

This work describes the development of a solid phase spectrophotometry method in a mSI-LOV system for cadmium, zinc, and copper determination in freshwaters. NTA (Nitrilotriacetic acid) beads with 60-160 mu m diameter were packed in the flow cell of the LOV for a mu SPE column of 1 cm length. The spectrophotometric determination is based on the colourimetric reaction between dithizone and the target metals, previously retained on NTA resin. The absorbance of the coloured product formed is measured, at 550 nm, on the surface of the NTA resin beads in a solid phase spectrophotometry approach. The developed method presented preconcentration factors in the range of 11-21 for the metal ions. A LOD of 0.23 mu g L-1 for cadmium, 2.39 mu g L-1 for zinc, and 0.11 mu g L-1 for copper and a sampling rate of 12, 13, and 15 h(-1) for cadmium, zinc, and copper were obtained, respectively. The proposed method was successfully applied to freshwater samples.

The main aim of this study was to investigate the performance of an aerobic granular sludge sequencing batch reactor (AGS-SBR) receiving water streams supplied with different loads of Zn(2+) (50 and 100 mg L(-1)) during an operation of 866 cycles (ca. 109 days). When the metal was not fed, chemical oxygen demand (COD), PO4(3-) and NH4(+) were efficiently removed, with efficiencies of 56, 23 and 72% respectively. DGGE profiles showed that Zn(2+) supply negatively affected the bacterial diversity and community structure of the granules. Consequently, the shock loadings with Zn(2+), particularly at the higher levels (100 mg L(-1)), affected the nutrient removal in the AGS-SBR, although the reactor still generally complied with admissible legal values concerning organic matter, nitrogen and Zn. Simultaneous removal of PO4(3-) and TSS in such conditions needs further refining but the application of aerobic granular SBR in the treatment of Zn(2+) contaminated wastewaters seems viable.

Submitted by Anabela Morais (ajmorais@porto.ucp.pt) on 2011-10-20T10:33:13Z No. of bitstreams: 1 com-inter_2010_UA_361006003_Mesquita_Raquel_01.pdf: 54111 bytes, checksum: cfab1c324aa72ebfc6557108a8d56dcf (MD5) Made available in DSpace on 2011-10-23T19:01:53Z (GMT). No. of bitstreams: 1 com-inter_2010_UA_361006003_Mesquita_Raquel_01.pdf: 54111 bytes, checksum: cfab1c324aa72ebfc6557108a8d56dcf (MD5) Previous issue date: 2010 info:eu-repo/semantics/publishedVersion

Submitted by Ana Costa (apcosta@porto.ucp.pt) on 2010-09-21T16:31:34Z No. of bitstreams: 1 Flow injection determination of fluoride.pdf: 1146199 bytes, checksum: 69277839286c54d66a8498d6fdf110b8 (MD5) Made available in DSpace on 2011-09-13T16:16:55Z (GMT). No. of bitstreams: 1 Flow injection determination of fluoride.pdf: 1146199 bytes, checksum: 69277839286c54d66a8498d6fdf110b8 (MD5) Previous issue date: 2009

Submitted by Ana Costa (apcosta@porto.ucp.pt) on 2010-09-21T16:53:38Z No. of bitstreams: 1 Sequential injection system.pdf: 1131722 bytes, checksum: 0fdc4255fce1a48245cc92737df44e41 (MD5) Made available in DSpace on 2011-09-13T16:31:00Z (GMT). No. of bitstreams: 1 Sequential injection system.pdf: 1131722 bytes, checksum: 0fdc4255fce1a48245cc92737df44e41 (MD5) Previous issue date: 2009

Submitted by Ana Costa (apcosta@porto.ucp.pt) on 2010-09-21T14:48:35Z No. of bitstreams: 1 Desenvolvimento de uma metodologia de análise.pdf: 680449 bytes, checksum: 109b9bab1a96e8b3743cffa085a68a95 (MD5) Made available in DSpace on 2011-09-13T14:37:48Z (GMT). No. of bitstreams: 1 Desenvolvimento de uma metodologia de análise.pdf: 680449 bytes, checksum: 109b9bab1a96e8b3743cffa085a68a95 (MD5) Previous issue date: 2009

Submitted by Teresa Monteiro (tlago@porto.ucp.pt) on 2011-07-12T14:24:31Z No. of bitstreams: 1 trab-int_2008_ESB_27_Mesquita_Raquel_01.pdf: 445227 bytes, checksum: df29f5813853711fe5781c432213032e (MD5) Made available in DSpace on 2011-10-07T17:38:59Z (GMT). No. of bitstreams: 1 trab-int_2008_ESB_27_Mesquita_Raquel_01.pdf: 445227 bytes, checksum: df29f5813853711fe5781c432213032e (MD5) Previous issue date: 2008

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Submitted by Teresa Monteiro (tlago@porto.ucp.pt) on 2011-07-12T11:40:05Z No. of bitstreams: 1 trab-int_2007_ESB_27_Mesquita_Raquel_01.pdf: 771425 bytes, checksum: c8589ea1867420e1da909459a3f6bc1b (MD5) Made available in DSpace on 2011-10-24T11:31:19Z (GMT). No. of bitstreams: 1 trab-int_2007_ESB_27_Mesquita_Raquel_01.pdf: 771425 bytes, checksum: c8589ea1867420e1da909459a3f6bc1b (MD5) Previous issue date: 2007

A flow injection multisite detection system was developed for correction of the sample blank in a colorimetric determination. By using detector relocation, a single spectrophotometer is used for the sequential reading of the sample blank and of the colored product; the sample crosses the flow cell to measure intrinsic absorption, the color reagent is subsequently added, and the flow cell is relocated to provide the reading of the resulting plug. The subsequent detector relocation immediately after peak maximum increases the determination frequency. This strategy was tested in the colorimetric determination of iron in soil samples based on the reaction of Fe (II) with 1,10-phenanthroline after reduction of Fe (III) to Fe (II) by ascorbic acid. The results obtained for 15 soil extracts were in good agreement with those obtained by the reference procedure. Relative standard deviations better than 4% were obtained, with a sampling rate of 30/h.

A gas diffusion sequential injection system for spectrophotometric determination of free chlorine is described. The detection is based in the colorimetric reaction between free chlorine and a low toxicity reagent o-dianisidine. A gas diffusion unit is used to isolate free chlorine from the sample in order to avoid possible interferences. This feature results from the conversion of free chlorine to molecular chlorine (gaseous) with sample acidification. With minor changes in the operating conditions, two different dynamic ranges were obtained enhancing the application both to water samples and bleaches. The results obtained with the developed system were compared to the reference method, iodometric titration and proved not to be statistically different. A detection limit of 0.6 mg ClO−/L was achieved. Repeatability was evaluated from 10 consecutive determinations being the results better than 2%. The two dynamic ranges presented different determination rates: 15 h−1 for 0.6–4.8 mg ClO−/L (water samples) and 30 h−1 for 0.047–0.188 g ClO−/L (bleaches).