AUTOCLAVED SEA-WATER AS A REFERENCE MATERIAL FOR THE DETERMINATION OF NITRATE AND PHOSPHATE IN SEA-WATER

A method for the preparation of a stable and reliable reference material for nutrients in sea water was developed, using autoclaving as a stabilization process. Attention was focused on nitrate and phosphate and the effect of autoclaving on their concentration was studied. The precipitation and redissolution of phosphate salt was overcome with an appropriate preacidification of the water to be autoclaved. Homogeneity and stability were checked for up to 14 months together with any possible adverse effect from light or cap contact with the sample. The reproducibility of the concentrations throughout the bulk of samples and as a function of time is greater than the currently stated precision of the determination for either nutrient. Such samples satisfy the requirements to be met by a reference material for nitrate and phosphate in sea water.