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| Author(s): |
Ana Clara Felix Vida
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB) |
| Defense date: | 2015-11-27 |
| Examining board members: |
Elias Ayres Guidetti Zagatto;
Emanuel Carrilho;
José Anchieta Gomes Neto;
Wanessa Melchert Mattos;
Ana Rita de Araujo Nogueira
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| Advisor: | Elias Ayres Guidetti Zagatto |
| Abstract | |
Different approaches to analytical flow systems involving relatively slow chemical reactions were developed. Zone trapping inside the reaction coil enables sensitivity improvements in flow-based spectrophotometric procedures relying on catalytic reactions. The reaction time and/or temperature can be increased for the determination of analytes present in the samples at low concentrations. Exploitation of the strategy avoids the liberation of air bubbles in the analytical path when high temperatures are involved. A flow injection system with zone trapping in the main reactor was developed for the spectrophotometric determination of cobalt in grass samples exploiting the oxidation of Tiron by bromate catalised by Co(II). Good figures of merit such as repeatability [r.s.d. = 0.8% for 0.6 ?g L-1 Co(II), (n = 5)], detection limit [0.046 ?g L-1 Co(II)], sampling frequency [19 h-1] and reagent consumption (330 ?g of Tiron for determination) were attained. Recovery data in grass sample digests varied within 97% e 113%. Zone trapping inside the flow-through cuvette for exploiting high temperatures was also promising for relatively slow reactions, as no liberation of air bubbles was noted even for temperatures as high as 95oC. The approach was applied to the spectrophotometric determination of vanadium in mineral water samples relying on the oxidation of p-anisidine by bromate catalised by V(V) at 95ºC. Good analytical figures of merit such as repeatability [r.s.d. = 2.1% for 5.0 µg L-1 V(V), n = 10], detection limit [0.1 µg L-1 V(V), sample frequency (25 h-1) and reagent consumption (3.0 mg of p-anisidine per determination) were attained. Additionally, an analytical procedure to monitor the potentially leachable ametryn and atrazine residues in soil samples was proposed. As leaching is relatively slow, a sequential injection system was used to perform the herbicide extractions with 0.01 mol L-1 CaCl2 and in-line solid phase extraction followed by elution towards a C18 monolithic column connected to a liquid chomatograph. To this end, the outlet of the column was connected to a 300-µL six-port valve. Regarding analytical performance, enrichment factors and detection limits were 10.2 and 18.8 and 0.016 e 0.015 mg L-1 for ametryn and atrazine, respectively, quantification limits were 0.05 mg L-1 for both herbicides and good repeatability (r.s.d. = 6.3 and 5.1 % for 0.05 mg L-1 of ametryn and atrazine, n = 10) were attained. Recovery data in the soil extracts under equilibrium conditions were within 85 and 99% (AU) | |
| FAPESP's process: | 11/08011-6 - Novel approaches for exploiting relatively slow chemical reactions in flow analysis. Applications to samples of environmental and agronomical relevance. |
| Grantee: | Ana Clara Felix Vida |
| Support Opportunities: | Scholarships in Brazil - Doctorate |