Development of microfluidic pre-concentration system for metals in seawater

In-situ marine biogeochemical sensing allows measurement at high frequency to investigate short and long-term variability in processes in ocean waters. In trace analyses, not only the low concentrations of analytes but also possible interferences from the matrix and other elements must be considered, therefore a pre-concentration step prior to the determination of trace metals needs to be implemented. The way forward for improved in-situ analyses of manganese in seawater was to build on the existing technology of the Sensors Group at NOC, Southampton and develop a pre-concentration system for coupling to spectrophotometric Lab on a Chip (LOAC) technologies. This thesis describes the development and optimisation of LOAC analyser for manganese determination in aquatic environments, integrated with pre-concentration. Optimised conditions for the extraction of manganese from seawater with a Toyopearl iminodiacetate resin column were developed using Mn-54 tracer. Conditions evaluated were optimal pH for manganese removal, optimal flow rate required for full recovery of manganese, and the concentration and the volume of the acid solution needed for quantitative elution of manganese from the resin.The LOAC system used the colorimetric 1-(2-Pyridylazo)-2-naphthol (PAN) method for Mn determinations. The modified method was used for manganese determinations, when sodium dodecyl sulfate (SDS) was used as surfactant, with calibration curves constructed and precision (in the range 1.08 - 3.81 % RSD) and the LOD of the method assessed (3SD, typically 14 nM with 10 cm cell).Results of the adaptation of the modified PAN method on the chip and its coupling to a resin column for collection of manganese proves the concept of on-chip pre-concentration.The design and production method of the microfluidic chips and the operation procedure of the bench-top LOAC manganese determination system with the resin column implemented on the chip are described. The LOAC system coupled with the resin column and PAN chemistry was used for manganese determination with calibration curve constructed and precision of the method determined (0.86 - 2.69 % RSD).