Study of enhancement effects in the chemiluminescence method for Cr(III) in the ng 1-1 range

A procedure is developed for the determination of Cr(III) to 1 ng l(-1) (2 x 10(-11) mol l(-1)) in alkali samples by means of H2O2-luminol based chemiluminescence (CL). The significant improvement in sensitivity from the previous CL methods for this metal is achieved by a modified design of the flow cell, utilizing the carbonate and bromide enhancement effect, and adapting the experimental parameters that have not been explored previously, such as metal impurities and the initiation time after mixing carbonate and hydrogen peroxide. The importance of these experimental parameters and the carbonate enhancement effect are discussed based on knowledge of the mechanism of oxidation of luminol and decomposition of H2O2 in the presence of metal ions. (C) 2000 Elsevier Science B.V. All rights reserved.