Analysis of river water samples utilising a prototype industrial sensing system for phosphorus based on micro-system technology

Abstract

The application of a phosphorus monitoring device based on microsystems technology (MST) to the analysis of river water is presented. An alternative to the standard molybdenum blue method known as the yellow vanadomolybdophosphoric acid method has been very effectively implemented. The method is simple, a reagent and sample are mixed in a 1:1 ratio forming a yellow complex that absorbs strongly below 400 nm in the UV spectrum. The kinetics of the reaction are rapid and sample turnaround is typically 3 min at room temperature. Therefore a very uncomplicated microfluidic design can be adopted. The working wavelength was chosen as 380 nm to coincide with the peak output of a UV-LED narrow bandwidth light source recently developed by Nichia. The limit of detection for the yellow method in the microfluidic system is 0.2 ppm with a dynamic linear range from 0-50 ppm. The method was applied to a measurement of phosphorus in a local river at specific sampling points along its course.

Hydrochemical processes in lowland rivers: insights from in situ, high-resolution monitoring

“…Integrated chips with separation and detection have been developed (and even used in the field) to measure streamwater P concentrations (Kang et al, 2001;Bowden et al, 2002a;Chen et al, 2006b). Most of the work on developing environmental methods for field applications has involved sensors or microfluidic devices for single analytes, or new miniature in situ water samplers, where the sample is recovered and analysed using conventional laboratory instrumentation (Bowden et al, 2002b;Datta and Banerjee, 2007;Gkritzalis-Papdopoulos et al, 2012;Jokerst et al, 2012). For field use, a lab-on-a-chip device of this nature offers huge potential advantages over existing in situ continuous monitoring technologies, because of robustness, reduced power and reagent requirements, reduced waste burden, and the capability to be hidden discretely to minimise interference by vandals (Ramirez-Garcia et al, 2008;Jokerst et al, 2012).…”

Development and Deployment of a Microfluidic Platform for Water Quality Monitoring

“…Salicylate was also used as a replacement for phenol, and was found to yield broadly similar analytical performance in terms of the sensitivity, and kinetics, while having the major advantages of being highly stable and non-toxic. Diamond and co-workers [29,30] evaluated the yellow vanadomolybdophosphoric acid method as an analytical method for the determination of phosphate in water within a microfluidic device with the aim of producing an automated device with a field-deployable lifetime of one year. In this method ammonium molybdate, (NH 4 ) 6 3 .…”

“…The resulting solution has a distinct yellow colour arising from the strong absorbance of this complex below 400 nm. It was shown that batches of the reagent could be used for over a year without significant loss in performance [29]. This method was therefore selected in preference to the molybdenum blue method, due to the greater stability of the reagents used in the analysis, and resulted in an assay with an LOD of 0.2 mg L -1 and a dynamic linear range of 0-50 mg L -1 .…”

Autonomous field-deployable device for the measurement of phosphate in natural water

“…The reaction takes place over 2 to 60 minutes depending on temperature and absorbs below 400nm. This allows the use of an LED and Photodiode for the absorbance measurement [11,12]. The only major drawback of this reagent is that it is composed of an aggressive acid that readily corrodes stainless steel.…”