THE 1993 QUASIMEME LABORATORY-PERFORMANCE STUDY - NUTRIENTS IN SEA-WATER AND STANDARD SOLUTIONS

The 1993 QUASIMEME nutrients laboratory-performance study is presented. The three parts were intended to test various analytical ranges or aspects. Part 1 was a single exercise at three concentration levels, while Part 2 addressed the problem of long-term repeatability testing, both using natural seawater samples. Part 3 was also a long-term repeatability exercise but using nutrient concentrates which required dilution (by participants) in low nutrients seawater. The results show that at medium and high concentration levels the relative standard deviation is about 10% for nitrate + nitrite, nitrite and phosphate, and 30-40% for ammonia, which is evidently a problem for most analysts. Calculations of Z- and P-scores show that 80-90% of the participants meet the target performance at the high concentration level and that the majority of errors are systematic and consequently should be readily correctable by strict application of reliable procedures.