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- Sequential injection methodology for carbon speciation in bathing watersPublication . Santos, Inês C.; Mesquita, Raquel B. R.; Machado, Ana; Bordalo, Adriano A.; Rangel, António O. S. S.A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO2), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO2 and TC was based on colour change of bromothymol blue (660 nm) after CO2 diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO2. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611 nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24-3.5 mg C L-1), CO2 (1.0-10 mg C L-1), TC (0.50-4.0 mg C L-1) and alkalinity (1.2-4.7 mg C L-1 and 4.7-19 mgC L-1) with limits of detection of: 9.5 mu g C L-1, 20 mu g C L-1, 0.21 mg C L-1, 0.32 mg C L-1, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.
- Use of solid phase extraction for the sequential injection determination of alkaline phosphatase activity in dynamic water systemsPublication . Santos, Inês C.; Mesquita, Raquel B.R.; Bordalo, Adriano A.; Rangel, António O.S.S.In this work, a solid phase extraction sequential injection methodology for the determination of alkaline phosphatase activity in dynamic water systems was developed. The determination of the enzymatic activity was based on the spectrophotometric detection of a coloured product, p-nitrophenol, at 405 nm. The p-nitrophenol is the product of the catalytic decomposition of p-nitrophenyl phosphate, a noncoloured substrate. Considering the low levels expected in natural waters and exploiting the fact of alkaline phosphatase being a metalloprotein, the enzyme was pre-concentrated in-line using a NTA Superflow resin charged with Zn2þ ions. The developed sequential injection method enabled a quantification range of 0.044–0.441 unit mL 1 of enzyme activity with a detection limit of 0.0082 unit mL 1 enzyme activity (1.9 mmol L 1 of pNP) and a determination rate of 17 h 1. Recovery tests confirmed the accuracy of the developed sequential injection method and it was effectively applied to different natural waters and to plant root extracts.