The paper reviews the methods described in the literature for the determination of total dissolved free primary amines (TDFPA) by fluorescence. A wide set of reaction conditions can be found, but they rely on few experiments for their validation. Among fluorogenic compounds, o-phthaldialdehyde (OPA) is more sensitive than fluorescamine and was thus examined here. However, the use of mercaptoethanol (ME) in the reaction (as an additional derivatization compound) is able to generate unreliable results, in particular when standardization relies on glycine. We suggest replacing ME with 3-mercaptopropionic acid (MPA) which induces more stable and comparable fluorescence among amine compounds. A systematic study was therefore undertaken to define reagent concentrations and pH effects on the reaction rates for a variety of primary amines with particular focus on amino acids. The reaction rate is increased by increasing OPA concentration and pH, but slowed by excess MPA. Ammonium interference is influenced by several factors, but spectral investigation showed that the choice of conditions can drastically reduce it. The magnitudes of natural and OPA-induced background fluorescence signals have been assessed in various mediums and it is shown that their contribution to the signal amounts to a large fraction, when not most, of the measured fluorescence. A segmented flow method is proposed with a protocol for adequate correction of biases.

Dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) measured in deep profiles in the N-E Atlantic and in the N-W Mediterranean in the period 1984-2002 are described. After accurate validation, they show close agreement with those previously published.Classic profiles were obtained, with concentrations decreasing in deep waters. In the Mediterranean and in the Atlantic comparable concentrations were found in the 1500-2000 m waters, 44-46 mumol 1(-1) DOC, 2.6-2.8 mumol 1(-1) DON and 0.02-0.03 mumol 1-1 DOP. In the surface layers, DOC concentrations were higher, but DON and DOP concentrations lower, in the Mediterranean than in the Atlantic, leading to higher element ratios in the Mediterranean. In autumn, values were, respectively, DOC:DON similar to17 vs. similar to14, DOC:DOP similar to950 vs. 500 and DON:DOP similar to55 vs. 35. The data suggest an increase in DOC and DON in the North Atlantic Central Water over 15 years, which may be linked to the North Atlantic climatic oscillations.Refractory DOM found in the 1500-2000m layer exhibited C:N:P ratios of 1570:100:1. The labile + semi-labile (= non-refractory) DOM (nrDOM) pool was computed as DOM in excess of the refractory pool. Its contribution to total DOM above the thermocline in the open sea amounted to 25-35% of DOC, 30-35% of DON, and 60-80% of DOP. Element ratios of the nrDOM varied among stations and were lower than those of refractory DOM, except for C:N in the Mediterranean: nrDOC:nrDON similar to10-19, nrDOC:nrDOP similar to160-530 and nrDON:nrDOP similar to15-38. The specific stoichiometry of DOM in the Mediterranean led us to postulate that overconsumption of carbon is probably a main process in that oligotrophic sea.By coupling non-refractory DOM stoichiometry and relationships between the main DOM elements in the water column, the relative mineralization of C, N and P from DOM was studied. Below the thermocline, the preferential removal of phosphorus with regard to carbon from the semi-labile DOM can be confirmed, but not the preferential removal of nitrogen. In the ocean surface layers, processes depend on the oceanic area and can differ from deep waters, so preferential carbon removal seems more frequent. Bacterial growth efficiency data indicate that bacteria are directly responsible for mineralization of a high proportion of DON and DOP in the deep water. (C) 2004 Elsevier Ltd. All rights reserved.

Two cruises (April and June 1997) were carried out in the Bay of Seine, a nitrate- and ammonium-enriched ecosystem of Western Europe, to identify the major mechanisms that control delta(15)N and VC in spring particulate organic matter (POM). Particulate organic nitrogen (PON) delta(15)N ranged between 0.8 and 5.2parts per thousand in April and between 2.2 and 6.2parts per thousand in June, while particulate organic carbon (POC) delta(13)C ranged between -24.3 and -19.7parts per thousand, and between -20.0 and -16.2parts per thousand during the same periods. During spring 1997, POM was highly dominated by autochthonous phytoplankton. It is shown that the variation of PON delta(15)N is due to both nitrate mixing between river and marine waters and fractionation of N stable isotopes during nitrate utilization by phytoplankton. Therefore, similarly to what was previously shown for open ocean, delta(15)N can be used as a proxy of spring fractional nitrate utilization in coastal ecosystems. It is also shown that POC delta(13)C in spring is controlled by POC concentration and C:N ratio (in addition to 'temperature effects'), which are considered here as indicators of primary production and phytoplankton degradation, respectively. The co-variation of delta(13)C and delta(15)N describes the spring phytoplankton dynamics: at the start of phytoplankton development, nitrate concentration is high (low delta(15)N) and phytoplankton production is low (low delta(13)C); then primary production increases (delta(13)C becomes higher) and the nitrate pool diminishes (deltadelta(15)N becomes higher); at a later stage, the nitrate pool is depleted (high delta(15)N), part of the phytoplankton becomes degraded and production is still high (high delta(13)C).

Phosphorus forms with respect to sediment characteristics, such as grain-size, and major chemical elements, were studied in French coastal marine areas (the Bay of Seine and the Loire and Gironde Estuaries).In the three areas, Fe/Al-bound phosphate (Fe/Al-P) and exchangeable phosphate (exch-P) were significantly related to the proportion of fine fraction (< 63 mum). The special association of these forms with fine particles, as well as the relationships between exch-P, Fe/Al-P and Fe showed that adsorption processes on Fe oxides had taken place. However, for similar Fe concentrations, Bay of Seine sediments showed Fe/Al-P concentrations which were four to five times higher than those found in the Loire and Gironde Estuaries. This was attributed to differences in sediment nature and processes in these two types of areas. Indeed, the Loire and Gironde Estuaries frequently show hypoxia.Calcium-bound phosphate (Ca-P) was found in all grain size classes with comparable concentrations in the Bay of Seine where there was no correlation between Ca-P and Ca. This corresponded to the calcium's marine origin (shells) in the Bay of Seine. In contrast, the correlation of Ca-P with Ca and the fine fraction of the sediment in the Loire and Gironde Estuaries was characteristic of the predominant metamorphic origin of Ca-P in these areas.Useful information for interpretation of P-forms can be obtained from major sediment characteristics. Thus, for areas where specific relationships have previously been established good estimates of P-forms could be predicted from sediment properties. (C) 2001 Academic Press.

A version of the orthophthaldialdehyde-fluorescence ammonium determination for flow injection analysis (FIA) is presented here, with a view to its use for in situ, low-power consumption systems. Thus, the reaction temperature was limited to 30 degrees C and FIA was used in stop-flow mode (3 min stop). The calibration is linear up to 50 mumol l-1, but concentrations up to 100 mumol l-1 can be measured. Repeatability is around 1% in the range of 0.5-4 mumol l-1 and the detection limit is about 0.03 mumol l-1. Over the salinity range of 5-35 (seawater practical salinity scale) the salt effect is almost negligible (within +/- 2%); and below salinity of 5 it increases to a maximum of -9% in fresh water compared to seawater. Hydrogen carbonate, dissolved oxygen and turbidity (either suspended sediments or phytoplankton cells) have almost no adverse effect in a wide range of concentrations, covering most natural water conditions. Relative interference of primary amines is negligible and mercury (a common sample preservative) does not depress the signal up to 20 mg l-1 Hg II. Sulfide, that may be present in areas with anoxic waters, depresses the signal only slightly and linearly (-9% at 100 mumol l-1 S2-). The method appears to be convenient for the determination of ammonium in most coastal, estuarine and fresh waters. Sample throughput is 9 h-1. The performance of the method can be improved, either by increasing the reaction time (low throughput) or, if enough energy is available, by increasing the reaction temperature (non-stop-flow mode, high throughput). Combining FIA and fluorometry appears to be interesting for in situ determination (submersible devices) of dissolved compounds in environments with variable salinity and turbidity (especially coastal and estuarine waters).

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 μmol l−1 and the limit of detection 0.02 μmol l−1. Linearity was tested up to 5 μmol l−1 of DOP, i.e. far above naturally occurring values. A throughput of 20 samples per hour is easily achieved.

Extractable organic copper using C18 Sep-Pak cartridges was investigated in seawater after laboratory experiment showed that the (C18 Sep-Pak) cartridges were reliable, in open and coastal waters with normal levels of dissolved organic carbon, for the separation of a specific fraction of organo-copper complexes.Given that the Sep-Pak cartridges retain the hydrophobic fraction of the dissolved organic matter, this extraction technique was applied for studying the characteristics of this particular hydrophobic dissolved organic copper fraction (hDOCu) in the north-western Mediterranean waters. Surface distribution of hDOC is influenced by organic matter input from the river Rhone and its estuary as well as the physical processes affecting the primary productivity such as coastal upwelling. By correlating hDOCu concentrations with total dissolved copper and other hydrochemical data such as salinity and dissolved organic carbon, it was possible to examine the behaviour of hDOCu in the water masses of different sources and ages.Marine organic matter has been shown to have high complexing capacity. Productive superficial and intermediate waters as well as deep waters showed relatively high and comparable complexing capacity indicating that old organic matter may have strong complexing sites. (C) 2000 Academic Press.

The accurate measurement of ammonium concentrations is fundamental to understanding nitrogen biogeochemistry in aquatic ecosystems. Unfortunately, the commonly used indophenol blue method often yields inconsistent results, particularly when ammonium concentrations are low. Here, we present a fluorometric method that gives precise measurements of ammonium over a wide range of concentrations and salinities emphasizing submicromolar levels. The procedure not only solves analytical problems but also substantially simplifies sample collection and preservation. It uses a single working reagent (consisting of orthophthaldialdehyde, sodium sulfite, and sodium borate) that is stable for months when stored in the dark. The working reagent and sample can be mixed immediately after sample collection and the reaction proceeds to completion within 3 h at room temperature. Matrix effects and background fluorescence can be corrected without introducing substantial error. This simple method produces highly reproducible results even at very low ammonium concentrations.

As part of the Programme National d'Oceanographie Cotiere, the nutrient dynamics of the Bay of Seine were studied between 1992 and 1994 in order to complement work on ecological modelling. Firstly, the River Seine's nutrient fluxes were established: 80 000-130 000 t a(-1) of dissolved inorganic nitrogen, 6 400-8 400 t a(-1) of dissolved phosphorus and 20 000-77 000 t a(-1) of dissolved silicium. Estuarine processes were taken into account. Consequences of nutrient loading for the bay were then evaluated at the pelagic level (nutrient and chlorophyll enrichments) and the benthic level (distribution of various phosphorus fractions in superficial sediments). The large continental inputs always induce concentration gradients in the water from the mouth of the river to the northwest of the bay. The northward spreading of fine particulate matter controls the distribution of adsorbed phosphate and iron-aluminium bound phosphate in sediments. In contrast, calcium bound phosphate, the main fraction in sediments, is not affected by river inputs. Organic phosphorus in sediments is related to phytoplankton blooms, with increasing concentrations during productive periods; afterwards the fast recycling prevents sedimentary accumulation. The nutrient depletions observed beyond the turbid plume during spring 1992 enabled the calculation of nutrient uptake rates, and the comparison of these rates with phytoplankton biomass (chlorophyll a + phaeopigments). Ratios of nutrient consumption to pigment concentration were estimated at 1 mu mol mu g(-1) for nitrogen, 0.05 for phosphorus and 0.5 for silicate. These values, as N/P and Si/N uptake ratios (respectively 17.5 and 0.4), were similar to usual values. (C) Elsevier, Paris.

The first application of pasteurization to stabilize seawater samples for subsequent nitrate and nitrite determination in marine water is presented. Coastal seawater sampled from winter to late spring, with various chemical characteristics, was used. Samples were filtered through 0.7 and 1 μm pore size membranes before being treated. Promising results were obtained since concentration changes in the samples did not exceed about 1–2% for both nutrients (i.e., an absolute change of 0.005 μmol l−1 for nitrite) over periods from 16 to 22 months. The efficiency of the treatment is shown by comparing the behaviour of treated samples to untreated ones. Although this stabilization method requires an oven for processing samples, it is advantageous in that it does not alter the samples by chemical additions and enables samples to be stored at room temperature for many months, without special equipment, before analysis.

activity reflect the peculiarities of the sea water composition around the vents. They are functionally dependent on the association between the macro-organisms, their symbiotic chemoautotrophic bacteria, the reduced chemicals present in the fluid (sulphide, methane...) and the oxygen of sea water (Fisher, 1990). Hydrothermal organisms are present along the mixing zone between the hot hydrothermal fluid and the cold sea water where both reduced (sulphide, methane) and oxidized (e.g. nitrate) compounds are available. This zone is subject to rapid and large spatio temporal variations of the environmental conditions as has been shown for temperature (Chevaldonné et al., 1991) and sulphide and silicate (Johnson et al., 1988). The chemical composition of the water surrounding the organisms remains yet to be adequately documented. This paper presents a summary of the results obtained on the chemical environment of the mussel clumps occurring at the Lucky Strike and Menez Gwen hydrothermal areas, Mid Atlantic Ridge, in order to elucidate the trends governing the functioning of the ecosystem and the interactions between fluid and organisms. Water samples were collected around the communities of Bathymodiolus sp. hydrothermal mussels during the DIVA 2 cruise (June 1994, on the N.O. Nadir and Nautile (Desbruyères et al., 1994) in two hydrothermal fields, Lucky Strike (1700 m depth) and Menez Gwen (850 m depth), located on the Mid Atlantic Ridge (MAR) (Fouquet et al., 1995; Van Dover et al., 1996), and analysed for chemical constituents.

The QUASIMEME Project (1993-1996) was established to assist European laboratories to improve the data they produce in marine monitoring programmes. Through laboratory performance Studies (with six-monthly reports), workshops and expert visits the programme was fully interactive.There were five rounds of laboratory performance studies. For the nutrient section, in which about 50 laboratories took part, the reference materials distributed to the participants consisted of standard solutions of nutrients and seawater samples stabilized by autoclaving. The material included low and high concentrations typical of those encountered in coastal seawater; at least two samples with different concentrations were distributed in each round.Robust statistics were used to determine the means and standard deviations for each set of results. For inorganic nutrients, the assessment of the data for bias and precision was based mainly on a Z- and P-scoring system in which targets of +/- 6% were allocated to the high concentrations, likewise +/- 12.5% to the low concentrations.This overview discusses overall performance separately for nitrate plus nitrite, nitrite, ammonia, phosphate, total nitrogen and total phosphorus, and classifies the performance of individual laboratories in each round, while maintaining their anonymity. Performance for nitrate plus nitrite and nitrite improved steadily and these determinands are now fully under control; at the end of the programme, standard deviations (SD) for nitrate plus nitrite were 0.2 mu mol l(-1) at low concentration and 0.6 mu mol l(-1) (4%) at high concentration, and for nitrite they were 0.03 mu mol l(-1) and 0.06 mu mol l(-1) (5%) respectively. Phosphate showed a somewhat stable level of performance with SD of 0.06 mu mol l(-1) and 0.10 mu mol l(-1) (10%) at low and high concentrations respectively, but this could be improved. Ammonia proved the most difficult to determine, and in spite of a substantial improvement at the beginning of the exercise, this determinand is not under control in many laboratories. At low concentrations, ammonia shows a positive bias of 0.2 mu mol l(-1) and a SD of 0.3 mu mol l(-1), while at high concentrations SD reaches 0.5 mu mol l(-1) (20%). For total nitrogen (TN) and total phosphorus (TP), the exercises show that only two thirds of the participants produced consistent data for TN, and less than half of them produced consistent data for TP. (C) 1997 Elsevier Science Ltd. All rights reserved.

Heat treatments, pasteurization and tyndallization, were tested as potential techniques for preservation of seawater samples for subsequent determination of nutrients (nitrate, nitrite, ammonia and phosphate), either for aquatic studies or for production of reference materials. The advantage over other methods is two-fold: there is no addition of preservative and no special equipment is required for sample storage. The effect of heating on nutrient concentrations was first examined, then long-term homogeneity and stability was assessed. Various types of sample bottles were used. Good physical characteristics of the bottles are essential, in particular air tight closure. Leaks introduce volatile compounds (ammonia, etc.) and bacteria. Nitrate and nitrite show satisfactory behaviour, with insignificant changes under heating and preservation over at least 1 year after pasteurization at a temperature of 65 °C, either in plastic or glass vials. Ammonia shows small concentration changes during the treatment. As ammonia is very sensitive to microbial activity, better stabilization is obtained if pasteurization is undertaken at a higher temperature (80–85 °C). Plastic bottles should be avoided since they are likely to be permeable to ammonia vapors and they favour its microbial consumption. Heat treatment for ammonia should be limited to reference materials, for which homogeneity and stability are the main requirements, with storage of up to several months and adequate checking. Phosphate also shows small changes under heating, but these can be greatly reduced by lowering the pH of the sample to about 7 before the treatment (preferably 80–85 °C). As glass leaches phosphate, plastic bottles are recommended for long-term storage (at least 6 months), but glass can be used for short-term storage or for well controlled reference material.

The distribution pattern and temporal variations of concentrations of phosphorus forms were studied in the sediments of the Bay of Seine in seven cruises over the period of 1992–1994. Calcium-bound phosphate (Ca-P) contributed over 50% of the sedimentary phosphorus pool, while exchangeable phosphate (exch-P) and Fe/Al-bound phosphate (Fe/Al-P) respectively made up less than 16% and 38% of total phosphorus. Concentrations of Ca-P were quite constant all over the bay, a consequence of the marine origin of the sediments' calcareous fraction. However, exchangeable phosphate and Fe/Al-bound phosphate (and thus total phosphorus) concentrations showed a mean east/west gradient highlighting the influence of particulate inputs from the Seine plume. Concentrations of inorganic phosphorus forms showed few temporal variations and are an almost permanent feature of the sediments. Finally, organic phosphorus (orga-P) was the only form to exhibit significant spatio-temporal variations. Its strong increase from winter to spring and summer can be related to phytoplankton growth, but remineralization prevents orga-P from accumulating. Potentially bioavailable phosphorus, constituted by orga-P and exch-P, represented mean proportions of no more than 20–40% of the total sedimentary phosphorus pool. This means that enrichment assessments based on total phosphorus alone are questionable. © 1997 Elsevier Science Ltd

The preparation and testing of reference material for nutrients for the QUASIMEME laboratory performance study 1993–1996 is described. Samples were prepared from natural, nutrient depleted seawater, which was then spiked with concentrated nutrient salt solutions, bottled and autoclaved. Concentrations were assigned according to the method of preparation. The materials were first analysed before and after the heat treatment, then immediately before each round and finally close to the end of that round. The results of the control of spike values and of homogeneity and stability are given. The assigned concentrations were compared with the robust means of the results of the participants and it is concluded that the material satisfied the requirements of the programme. This new type of reference material prepared for the programme can be defined as seawater matrix standard.

The chemical factors (inorganic nitrogen, phosphate, silicic acid) that potentially or actually control primary production were determined for the Bay of Brest, France, a macrotidal ecosystem submitted to high-nitrate-loaded freshwater inputs (winter nitrate freshwater concentrations >700 mu M, Si:N molar ratio as low as 0.2, i.e. among the lowest ever published). Intensive data collection and observations were carried out from February 1993 to March 1994 to determine the variations of physical [salinity, temperature, photosynthetically active radiation (PAR), freshwater discharges] and chemical (oxygen and nutrients) parameters and their impacts on the phytoplankton cycle (fluorescence, pigments, primary production). With insufficient PAR the winter stocks of nutrients were almost nonutilized and the nitrate excess was exported to the adjacent ocean, due to rapid tidal exchange. By early April, a diatom-dominated spring bloom developed (chlorophyll a maximum = 7.7 mu g l(-1); primary production maximum = 2.34 g C m(-2) d(-1)) under high initial nutrient concentrations. Silicic acid was rapidly exhausted over the whole water column; it is inferred to be the primary limiting factor responsible for the collapse of the spring bloom by mid-May. Successive phytoplankton developments characterized the period of secondary blooms during summer and fall (successive surface chlorophyll a maxima = 3.5, 1.6, 1.8 and 1.0 mu g l(-1); primary production = 1.24, 1.18 and 0.35 g C m(-2) d(-1)). Those secondary blooms developed under lower nutrient concentrations, mostly originating from nutrient recycling. Until August, Si and P most likely limited primary production, whereas the last stage of the productive period in September seemed to be N limited instead, this being a period of total nitrate depletion in almost the whole water column. Si limitation of spring blooms has become a common feature in coastal ecosystems that receive freshwater inputs with Si:N molar ratios <1. The peculiarity of Si Limitation in the Bay of Brest is its extension through the summer period.

The EU project ‘QUASIMEME’ was established to provide comprehensive knowledge of the quality of chemical measurements made in marine monitoring programmes, to determine the underlying causes of poor inter-laboratory agreement for these measurements and to provide stepwise improvement. The quality of analytical performance of all laboratories in the scheme has been established. During the project, 32 laboratories have improved their performance, 18 were consistently good, 16 were consistently poor and a further 10 have declined in performance. Overall, 34 of the 76 laboratories currently produce data which have >80% of values being satisfactory. Determinands and/or matrices which still present problems are low levels of ammonia in seawater, lead in biota, CB 28, CB 105 and CB 156 and some of the organochlorine pesticides.

Replies to the questionnaire on the determination of ammonia, sent to participants in the Fifth ICES Intercomparison Exercise for nutrients in seawater, are evaluated. The conclusions provide some useful recommendations for analysts. Berthelot's reaction (formation of indophenol-blue) is the basis of the colorimetry used by the great majority of participants, and their individual methods are examined in detail. Application of the indophenol-blue method to seawater poses some specific problems, for example, precipitation, and variation of the pH of the matrix as a function of salinity. Basic principles are discussed and participants' procedures are compared with those most commonly used in the literature. Large disparities in reaction and operating conditions are evident between these many versions of what is nominally the same method. Various points of the reaction mechanism are examined in order to determine optimal ranges for reagent concentrations. Procedures for calibration, measuring the blank, and defining the concentration-zero are also evaluated, as the intercomparison results indicate that systematic (particularly relative) errors are widespread. The use of low-nutrient seawater as a calibration matrix is strongly recommended if errors such as those incurred by the use of demineralised water or artificial seawater are to be avoided. Sources of contamination are discussed, the majority of participants being aware that ambient laboratory air can be a major problem. In general, users of automated methods produce better results than users of manual methods, but this may simply reflect a tendency for the former to be the more experienced analysts. Although it was not possible consistently to relate performance in the intercomparison with methodology, it would appear that many procedures deviate from optimal operating conditions, while some are unnecessarily complicated and might benefit from simplification. Analysts are invited to re-examine their ammonia methods, with particular attention to suitability of reagents and reaction conditions, use of adequate blank and calibration procedures and matrices, correction for refraction effects and identification of local contamination sources.

The Bay of Brest is a semi-enclosed coastal ecosystem receiving high nutrients loading from freshwater inputs. In order to analyse the response of phytoplankton stocks to increasing eutrophic conditions, a survey of the annual cycle of hydrographic properties, nutrients and chlorophyll a concentrations, and carbon uptake rates was performed at four stations in 1993. This database has been compared to earlier measurements performed during several comparable surveys within the last 20 years. As compared to the seventies, a doubled nitrate loading is now entering this ecosystem, which is related to increased agricultural activities on the drainage basins, while the geographical origin of the nitrate input has been modified. As a result of these anthropogenic modifications, summer averaged Si/N stoichiometric balance has decreased during the two last decades but, contrary to what has been observed in other coastal ecosystems, phytoplankton stocks have not increased. Several ecological factors have hindered eutrophication: the high hydrodynamic mixing with adjacent marine waters, caused by the macrotidal regime, induces important nutrients losses, temperature and mostly light limit primary production while Si and P high recycling maintain nitrogen limitation in this ecosystem. Conjunction of these non-anthropogenic factors explains the global stability of phytoplankton stocks.

The choice of model compounds for checking the recovery of dissolved organic and total dissolved phosphorus in natural waters is discussed. Ten compounds were compared for their recovery in fresh and seawater. Four different oxidative procedures were used: acidic and alkaline persulfate oxidation, continuous flow UV irradiation and high-temperature combustion (HTC). Certain compounds have been shown to decompose when heated for moisture removal. Due to impurities and moisture, HTC is therefore suggested as a reference method for model compounds, assuming 100% recovery of organic phosphorus as phosphate. Full recovery is to be expected for the compounds in fresh water, but not for seawater. Matrix effects vary according to the oxidative method, with recoveries as low as 50% or less for certain compounds. It is therefore recommended that several model compounds should be used, at least one labile (phosphoenolpyruvate, glycerophosphate or riboflavin-5-phosphate) and one refractory (aminoethylphosphonic acid, phytic acid or phosphorylcholine chloride). The alkaline persulfate method can be recommended for marine waters.