Abstract
This study presents an innovative technique for the in situ analysis of aquatic biochemical elements detected through wet chemical processes. A new compact in situ phosphate analyzer based on sequential injection analysis, liquid waveguide capillary flow cell and spectrophotometry was developed, and a safe and modular electronics-chemical separation mechanical structure was designed. The sequential injection system of this analyzer was optimized, and the major functions of this analyzer were studied and estimated. With a 10 cm liquid waveguide capillary flow cell and a 6.3 min time cost of detection, the analyzer reaches a detection limit of 1.4 μg·L−1 (≈14.7 nM, [PO43−]) and a consumption of 23 μL at most for each reagent. This analyzer was operated in situ and online during two scientific research cruises in the Pearl River Estuary and northern South China Sea. The advantages of this analyzer include its simple versatile manifold, full automation, low chemical consumption and electronics-chemical separate safe structure. Long-term in situ performance of this analyzer will be validated in the future.
Highlights
With the growing human footprint, the enrichment of nutrient inputs and pollution are significantly altering estuarine and coastal ecosystems [1,2,3,4]
The following were performed with the in concentration gradients of 0.05, 0.1, 0.2, 0.3, 0.4 mg·L−1 dissolved reactive phosphorus (DRP) ([PO43−]) series standard solutions prepared in ultrapure water
All the R2 values obtained from curve fitting were above 0.99, and the RSD of the slopes for different salinities is 1.63%; these results indicate that the effect of salinity on the analyzer was negligible and that a salinity correction was not required in the analyzer
Summary
With the growing human footprint, the enrichment of nutrient inputs and pollution are significantly altering estuarine and coastal ecosystems [1,2,3,4]. As an important routine macronutrient in natural waters [5], excess phosphate can generate noticeable effects on aquatic environments, such as eutrophication and coral reef decline [4,6,7]. Traditional analysis methods of nutrients in natural waters require the collection and freezing of discrete samples and subsequent analysis in the laboratory, and these methods are high cost in time and chemicals, susceptible to contamination of water samples and limited in long-term detection of marine nutrients [8,9,10]. Miniaturized autonomous in situ instrumentation provided with excellent performances (such as long-term serial monitoring and fast response time) helps to improve the observing capacities in the constantly changing marine environment [12]
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