Automated Determination of Dissolved Reactive Phosphorus at Nanomolar to Micromolar Levels in Natural Waters Using a Portable Flow Analyzer

Abstract

Automated in-field methods for measuring dissolved reactive phosphorus (DRP) over a large concentration range are in high demand for the purpose of better understanding the biogeochemistry of phosphorus in the river-estuary-coast continuum to the open ocean. Here, an automated portable and robust analyzer was described for the determination of nanomolar to micromolar levels of DRP in natural waters. The quantification of DRP was based on classic phosphomolybdenum blue (PMB) chemistry. All the components of the analyzer were computer-controlled using LabVIEW-based laboratory-programmed software. When equipped with a 3 cm Z-type flow cell, the system demonstrated linearity with concentrations up to 12 μmol L–1, a sampling rate of 20 h–1, a limit of detection of 0.11 μmol L–1, and relative standard deviations (RSDs) of 0.4–4.6% (n = 11–576). When a solid-phase extraction cartridge was combined with the analyzer, the PMB formed from the sample was automatically concentrated on the hydrophilic–lipophilic balanced sorbent. The concentrated PMB compound was eluted with NaOH solution and measured in the spectrophotometric system. Under optimal conditions, the nanomolar-level mode afforded a sampling rate of 8 h–1, a limit of detection of 1.7 nmol L–1, and RSDs of 3.0–5.7% (n = 11–120). The system exhibited advantages that included a wide linear range, high sensitivity and reproducibility, low reagent consumption, and insignificant interference from salinity, silicate, arsenate, and other P-containing compounds. The system was successfully applied for discrete sample analysis, fixed site online monitoring, and the real-time underway measurement of DRP in riverine-estuarine-coastal waters.

Real-Time Underway Mapping of Nutrient Concentrations of Surface Seawater Using an Autonomous Flow Analyzer

“…The parameters related to chemical reaction and flow analysis have been comprehensively evaluated and optimized in previous publications using i SEA-I. − With the updated version ( i SEA-II), these optimized values were checked and reconfirmed to be suitable for the new hardware. Table summarizes the analytical figures of the merit of the i SEA-II system after minor optimization.…”

“…Detailed information on chemical preparation can be found in the Supporting Information and previous papers. − …”

“…and system requirements (high reliability, low consumption, high frequency, etc. ). − Major advances in the development of devices utilizing different flow techniques (e.g., segmented continuous-flow analysis, , normal flow injection analysis, − reverse flow injection analysis, , sequential injection analysis, , microfluidic chips, − flow batch analysis, − programmable flow injection (pFI) in batch mode , ) to measure nutrients in seawater have been reported. Some of them have been applied for the underway measurement of specific single or dual-parameter nutrients in shipboard laboratories. ,− However, to the best of our knowledge, studies on the simultaneous underway analysis of all five key nutrients in estuarine and coastal waters are not available.…”

“…Recently, we developed a portable analyzer ( i SEA) for the on-site analysis of ammonium, nitrite/nitrate, and phosphate/silicate , in different aqueous samples. i SEA is robust and field-deployable without significant matrix effects.…”

LabVIEW virtual instrument for zone penetration studies in flow-based analytical systems

“…[27][28] LabVIEW VIs were also utilized for the precise control and monitoring of hardware components of automated SIA systems. [29][30][31] However, to the best of our knowledge, the open code LabVIEW software for zone penetration studies was not yet reported. Our main objective was to develop LabVIEW VI that would not only provide the user with the most fundamental peak-related parameters but it would also support zone penetration studies in flow-based analytical systems, by evaluating peak overlapping areas.…”