Quality improvement in determination of chemical oxygen demand in samples considered difficult to analyze, through participation in proficiency-testing schemes

Beltrán, J.; Borja, R.; Cavinato, C.; Clinckspoor, M.; De la Rubia, M. A.; Demirer, G.; Diamadopoulos, E.; Fernández - Cegrí, V.; Frigon, J. C.; Koubova, J.; Launay, M.; Menin, G.; Méndez, R.; Noguerol, J.; Raposo, F.; Uellendahl, Hinrich; West, S.