Photometric determination of cobalt. • At a pH > 5 cobalt(II) ions react with 4-[5-chloropyridyl-(2)-azo]-m-phenylene diamine (5-Cl-PADAB) to form a pink colour complex which, contrary to other heavy metal complexes, is also stable below pH 5. • Type standard test 1-51 • Range: 10 mm cuvette: 0.02 - 0.70 mg/l Co2+ ; 50 mm cuvette: 0.002 - 0.300 mg/l Co2+ • Sufficient for: 220 determinations • Sea water suitability: yes