Abstract
A segmented flow automated method with on-line photo-oxidation for the determination of dissolved organic phosphorus + soluble reactive phosphorus (DOP + SRP) in seawater and fresh water is described here. A low-power lamp was used for a compact, easy-to-handle and low-ozone-producing manifold. The influence of seawater matrix components was studied in detail using natural seawater and salt solutions spiked with DOP model compounds. Bromide was found to be the most inhibitory species in seawater. The work shows that most salt solutions referred to as artificial seawater are not satisfactory model matrices to test the actual seawater matrix effect. Since DOP recovered in undiluted seawater samples was about half that obtained in fresh water samples, the described method includes a 5- to 6-fold dilution of seawater samples. This simple procedure overcomes matrix effects and provides satisfactory DOP recovery. No pH effect was found in the 6-9 range corresponding to most natural waters. The standard deviation was 0.007 mu mol l(-1) and the limit of detection 0.02 mu mol l(-1). Linearity was tested up to 5 mu mol l(-1) of DOP, i.e. far above naturally occurring values. A throughput of 20 samples per hour is easily achieved. (C) 2001 Elsevier Science B.V. All rights reserved.
Highlights
Phosphorus is well known as an essential micronutrient for microalgae
The automated method described for Dissolved organic phosphorus (DOP) determination in seawater uses a low-power lamp for a compact, easy-to-handle and low ozone producing manifold
The segmented flow analysis (SFA) technique used provides much lower sample throughput than flow injection analysis (FIA), but FIA cannot achieve the precision provided by SFA (Zhang, 2000)
Summary
Phosphorus is well known as an essential micronutrient for microalgae. It is present in waters under various physico-chemical forms (Strickland and Parsons, 1972; McKelvie et al, 1995). With growing interest in the organic matter pool, several works have focused in the past decade on the accurate determination of DOP in marine waters (Ridal and Moore, 1990, 1992; Kérouel and Aminot, 1996; Ormaza-Gonzalez and Statham, 1996; Karl and Yanagi, 1997; Monaghan and Ruttenberg, 1999). The DIP pool consists mainly of orthophosphate, and includes pyrophosphate and inorganic polyphosphates (McKelvie et al, 1995; Thomson-Bulldis and Karl, 1998). SRP represents orthophosphate and potentially some -hydrolyzable DOP and inorganic phosphorus compounds that would react under the phosphomolybdate-blue method’s reaction conditions
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