Sequential injection system for the determination of alkaline phosphatase activity in natural waters and plant roots with in-line solid phase extraction

Abstract

The present work describes the development of a sequential injection system for the determination of alkaline phosphatase activity, after solid phase extraction/preconcentration and also the determination of phosphate in natural waters and plant roots. The determination of alkaline phosphatase activity was based on the sepctrophotometric detection of a colored product (p-nitrophenol), resulting from the catalysis of a non colored substrate (p-nitrophenyl phosphate). Due to the low levels of alkaline phosphatase in waters, it was preconcentrated in a NTA Superflow resin charged with Zn2+ ions. This was possible due to the enzyme necessity for metals in its active site. The phosphate determination was based on the spectrophotometric determination of a colored complex (molybdenum blue), resulting from the formation of the complex of orthophosphate with molybdate, followed by its reduction with ascorbic acid. The proposed methodology allowed the determination of alkaline phosphatase activity within a range between 0.044 – 0.441 unit cm-3 and 19 – 280 μmol dm-3 pNP. A determination rate of 17 h-1 and detection limits of 0.025 unit cm-3 and 1.9 μmol dm-3 pNP were obtained. Phosphate determination was also possible to perform within a range between 0.98 – 49.9 μmol dm-3 H2PO4 -, and with a detection limit of 0.29 μmol dm-3 H2PO4 -. A determination rate of 32 h-1 was obtained

Date of Award	2012
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	António O. S. S. Rangel (Supervisor) & Raquel Mesquita (Co-Supervisor)