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.