Chemiluminescent Determination of Chromium (VI) with 4-Methoxycoumarin and the Effect of Alkaline Solutions on the Chemiluminescence

The reverse flow-injection chemiluminescent determination (RFIA) of chromium(VI) was investigated with 4-methoxycoumarin in the presence of hydrogen peroxide and Zephiramine as a cationic surfactant. The chemiluminescent intensity on coumarin and nine kinds of coumarin derivatives were examined using RFIA. As a result, 4-methoxycoumarin was superior to coumarin and other derivatives; that is, 7-amino-4-methylcoumarin, 3,4-dihydrocoumarin, 5,7-dimethoxycoumarin, 4-hydroxycoumarin, 4-hydroxy-7-methoxycoumarin, 7-methoxycoumarin, 4-methylunbelliferone, umbelliferone. The chemiluminescent strength with chromium(VI) using these detection reagents was amplified after the addition of an alkaline solution. This phenomenon was based on the decomposition of detection reagents with an alkaline solution. The new detection reagent obtained with alkaline pretreatment was coumaric acid from coumarin, for example. The flow system was two channels. The detection of Cr(VI) by the proposed method was 2.1 ppb (S/N = 3). The limit of determination was 6.3 ppb. The conditions for the determination of Cr(VI) were follows : sample solution (line L(2)); Cr(VI); flow rate 0.3 mL/min, 1.8 % hydrogen peroxide (line L(1)); flow rate 0.6 mL/min, Tris solution (pH 9) (line SR); 3.0 X 10(-3) mol/L 4-methoxycoumarin (50 mu L). The proposed method was examined by reverse HA, because the coumarin derivatives were expensive. Normal FIA also obtained the same result.