4Metrohm.Application Bulletin No.114/1e:Polarographic determination of five metal ions (copper,cobalt,nickel,zinc and iron) in a single operation[EB/OL].2006-03-17.http:www.metrohrn.com.
5Metrohm.VA application Note No.V-41:cadmium,lead,copper,nickel and cobalt in soybean oil after digestion[EB/OL].2006-03-17.http:www.metrohm.com.