Reference material for nutrients for the QUASIMEME laboratory performance studies 1993–1996

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.