Chlorophyll-a determination: results of an interlaboratory comparison

A chlorophyll-a interlaboratory comparison was carried out to compare three different analytical chlorophyll-a determination methods: a German standard DIN 38412-16, a method of the HELCOM-Combine-Manual and the different “in-house” methods of participating laboratories. Eleven laboratories took part. They had to determinate the chlorophyll-a and phaeopigment content in two seawater samples taken from the Baltic Sea. Furthermore, for the assessment three different statistical evaluation methods were applied: the German standard DIN 38402-42, the Q-method combined with an estimator according to Huber and the Cofino-method. All analytical methods were appropriate to determine the chlorophyll-a content. The relative standard deviations of reproducibility for chlorophyll-a varied between 12 and 31%. None of the analytical methods was appropriate to determine the phaeopigment content quantitatively. The relative standard deviations of reproducibility for phaeopigments ranged between 87 and 158%. The applied statistical evaluation methods resulted in different assessments. The Q-method combined with an estimator according to Huber proved to be the best qualified method.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia