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| Author(s): |
Diogo Librandi da Rocha
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2013-06-24 |
| Examining board members: |
Fabio Rodrigo Piovezani Rocha;
Maria Encarnacion Vazquez Suarez Iha;
Marcos Yassuo Kamogawa;
Ana Rita de Araujo Nogueira;
Pedro Vitoriano de Oliveira
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| Advisor: | Fabio Rodrigo Piovezani Rocha |
| Abstract | |
Mechanization of sample preparation minimizes systematic errors, waste generation and analysis time. Flow-based systems with solenoid micropumps (MPFS) attain the requirements for mechanization in a versatile and robust way. Therefore, analytical procedures based on MPFS and on-line photo-oxidation were developed aiming phosphorus fractionation in foodstuff and river waters and chloride determination in natural waters and urine. Phosphorus is an important nutrient for plants and animals and its bioavailability depends on its chemical form, making fractionation studies important. Chloride monitoring is relevant because the concentration unbalance leads to environmental and health issues. A MPFS was proposed for the fractionation of water soluble phosphorus in foodstuff, incorporating on-line photo-oxidation of organic phosphorus to phosphate, which was quantified by the spectrophotometric molybdenum blue method. Linear response was observed from 5 to 40 mg L-1 for both inorganic (PI) and organic (PO) phosphorus, with detection limits of 0.5 and 1.2 mg L-1, respectively. Coefficients of variation (n = 20) were estimated as 1.2 and 3.6% for PI and PO, respectively, with a sampling rate of 80 determinations per hour. Per determination, 380 µg of (NH4)6Mo7O24, 620 µg of ascorbic acid and 790 µg of K2S2O8 were consumed, generating 2.5 mL of waste. The results for food extracts agreed with those obtained by the reference procedure (95% confidence level) based on nitro-percloric digestion for PO determination. A MPFS procedure with long pathlength spectrophotometry was developed for phosphorus fractionation (dissolved organic and inorganic) in natural waters. Quantification was also based on the formation of molybdenum blue, after on-line photo-convertion of the organic species to orthophosphate. The analytical response was linear within 10 and 75 µg L-1 with a detection limit of 2.0 µg L-1. Coefficient of variation of 1.8% and sampling rate of 40 determinations per hour were achieved. Per determination, 160 µg of (NH4)6Mo7O24, 10 µg of SnCl2, 640 µg of K2S2O8 and 10 mg of NaOH were consumed, generating 4.0 mL of waste. Slopes of analytical curves obtained for four different PO species agreed with those obtained for orthophosphate, indicating quantitative conversion and the results for five freshwater samples agreed with those obtained by the AOAC reference procedure at 95% confidence level. A green procedure for chloride determination in urine and natural waters was also developed, avoiding hazardous chemicals. The analyte was on-line photo-converted to chlorine which was spectrophotometrically detected by methyl orange discoloration. The analytical response was linear from 2.0 to 20 mg L-1 Cl with a detection limit of 0.7 mg L-1. The coefficient of variation was 1.6% with a sampling rate of 75 determinations per hour, consuming 7.5 µg of the dye per determination. Usual concomitant species did not cause significant interference even in excess in relation to their highest concentration expected in the samples. The results for urine and water samples agreed with those obtained by the reference procedures at the 95% confidence level. The proposed procedures are environmentally friendly and fast alternatives for phosphorus fractionation and chloride determination (AU) | |
| FAPESP's process: | 10/00700-4 - Development of flow-based procedures with multicommutation and online microdigestion for the determination of species in environmental and technological samples. |
| Grantee: | Diogo Librandi da Rocha |
| Support Opportunities: | Scholarships in Brazil - Doctorate |