THE QUASIMEME LABORATORY PERFORMANCE STUDIES (1993-1995) - OVERVIEW OF THE NUTRIENTS SECTION

The QUASIMEME Project (1993-1996) was established to assist European l aboratories to improve the data they produce in marine monitoring prog rammes. Through laboratory performance Studies (with six-monthly repor ts), workshops and expert visits the programme was fully interactive. There were five rounds of laboratory performance studies. For the nutr ient section, in which about 50 laboratories took part, the reference materials distributed to the participants consisted of standard soluti ons of nutrients and seawater samples stabilized by autoclaving. The m aterial included low and high concentrations typical of those encounte red in coastal seawater; at least two samples with different concentra tions were distributed in each round. Robust statistics were used to d etermine the means and standard deviations for each set of results. Fo r inorganic nutrients, the assessment of the data for bias and precisi on 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 s eparately for nitrate plus nitrite, nitrite, ammonia, phosphate, total nitrogen and total phosphorus, and classifies the performance of indi vidual 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 pro gramme, 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 conce ntration, 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 p erformance 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 sub stantial improvement at the beginning of the exercise, this determinan d is not under control in many laboratories. At low concentrations, am monia 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 sho w that only two thirds of the participants produced consistent data fo r TN, and less than half of them produced consistent data for TP. (C) 1997 Elsevier Science Ltd. All rights reserved.