Development of a flow method for the determination of phosphate in estuarine and freshwaters—Comparison of flow cells in spectrophotometric sequential injection analysis

Abstract

A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 μM PO(4)(3-)) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 μM) was achieved using both detection systems.

A Lab-On-Chip Phosphate Analyzer for Long-term In Situ Monitoring at Fixed Observatories: Optimization and Performance Evaluation in Estuarine and Oligotrophic Coastal Waters

“…For this reason, Clinton-Bailey et al (2017) recommended adding 0.01% (w/v) polyvynilpyrrolidone (PVP) to the ascorbic reagent since PVP is stable at low temperatures and yields linear calibration results of adequate sensitivity (albeit lower than that obtained with SDS). Interestingly, the need for a dispersant such as PVP or SDS in the reacting mixture appears to be specific to microfluidic instruments, considering that several mesofluidic flow methods operate satisfactorily without surfactant (Wu et al, 2001;Mesquita et al, 2011;Ma et al, 2014). This is likely due to the fact that microfluidic instruments have a surface area to volume ratio two or more orders of magnitude higher than mesofluidic instruments.…”

“…This salinity bias is purely optical and arises because of matrix dependent variations in light transmission through the measurement cells (Mesquita et al, 2011). At higher sample salinities, the incoming light is better directed toward the photodiode detector compared to deionized water samples.…”

Flow injection analysis as a tool for enhancing oceanographic nutrient measurements—A review

“…Since the light beam from the detector source enters the capillary almost orthogonal to the direction of flow through the capillary, the schlieren effect (discussed in Section 4) is also minimised, which is an important consideration in the analysis of waters of varying salinity. MRFCs have been used to advantage in a number of estuarine coastal marine studies [33][34][35][36][37][38].…”

Sequential injection system with multi-parameter analysis capability for water quality measurement

“…A low-cost colorimeter based on light-emitting diode (LED) as light source [12][13][14] and light dependent resistor (LDR) as light sensor was fabricated. The LED/LDR colorimetric detection is inexpensive and portable analytical equipment.…”