Abstract: 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°C and FIA was used in stop-Bow mode (3 min stop). The calibration is linear up to 50 µmol L-1, but concentrations up to 100 µmol L-1 can be measured. Repeatability is around 1% in the range of 0.5-4 µmol L-1 and the detection limit is about 0.03 µmol 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 µmol 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). (C) 2001 Elsevier Science Ltd. All rights reserved.

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 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.

Abstract: Methods for the determination of organic and total P in natural waters based on the hydrolysis and oxidation of all complexed forms of P to phosphate by acidic and alkaline persulfate oxidation, continuous-flow UV irradiation and high temperature combustion (HTC) were studied. Ten compounds were used to test the efficiency of these hydrolysis/oxidation reactions. The results indicated that in such methods, recoveries should be tested using model compounds with HTC as the reference method. One labile compound (phosphoenolpyruvate, glycerophosphate or riboflavin-5-phosphate) and one refractory compound (aminoethylphosphonic acid, phytic acid or phosphorylcholine) should be used to determine an upper and lower recovery, respectively. The recoveries depended on the matrix; quantitative recoveries were obtained with fresh water but not with seawater. For the determination of P in seawater the alkaline persulfate oxidation method is recommended.