Automated nutrients analysis for buoys in sea-water and intercalibration

The Nutrient Probe Analyser-4 (NPA-4) is an automatic chemical analyser for "in-situ" and continuous measurements, based on a new improvement of the exclusive analytical technology developed by Systea and named LFA (Loop Flow Analysis); LFA has permitted levels never reached before in analytical automation and in analyser miniaturisation. With NPA-4 probes, it is possible to analyse directly in the water up to four parameters with the same instrument, using a particular configuration of LFA technology, which allows the sequential analysis of more than one analytical method in a single analytical reactor (30 minutes for a complete 4 parameters cycle). It has been conceived to execute ammonium, nitrate-nitrite, nitrite and orthophosphate analysis at low concentration in sea water samples. The hermetic closed Loop provides full protection against background interference, a basic requirement for stable trace analysis. At the start of a cycle the loop is washed and filled with sample. The sample colour is measured for compensation. Small amounts of concentrated reagents are added and mixed with high intensity. The intensity of the colour of the reaction product is measured one or two colorimetric dual beam with silicon detector, depending on requested methods. The standard wet chemistries for nutrients analysis used in NPA-4 are the ones recommended by international standard The statistical test show that the results of automated and manual analyses agree for all the examined parameters. Precision of all four analyses is <= 3 % RSD. The Limit of detection of 5, 5, 2.5 and 2.5 ?g/L were reported for N-NH4, N-NO3, N-NO2 and P-PO4, respectively. Multiparametric on line analyzer: it is possible to connect to a data logger with analogue and digital signals, in order to have on line simultaneous analysis of the sample. A typical application is on line analysis of seawater on an oceanographic research buoy (Max -5m). It does not require any operator.