A fluorometric determination of boron was investigated by flow injection analysis with 2,3-dihydroxynaphtalene (2,3-DHN). In the determination of boron, a method using a boron-2,3-DHN-insulin ternary complex was attempted in order to remove any influence of excess reagent on the precision of boron determination. Catechol and chromotropic acid except 2,3-DHN as Huorometric reagents were examined from standpoint decreasing the effect of a large reagent blank value. As a result, 2,3-DHN was better than them as a fluorometric reagent. The flow system was composed of three channels, including the carrier (1.9 mL/min), reagent (a mixture of 2,3-DHN, Mn(II), H
2O
2) (0.9 mL/min) and insulin (0.2 mL/min). In the presence of Mn(II) and H
2O
2, 2,3-DHN formed a radical, which accelerated the formation of a ternary complex in an alkali solution at pH 11. With the reagent solution containing the radical, the ternary complex formed effectively at pH 7.6. The ratio of the boron-DHN complex composition in the ternary complex was boron: DHN = 1 : 2. On the other hand, the ratio between insulin and boron was 1 to above 1. A number of B-DHN complexes were connected to the surface of one insulin molecule. The B-DHN -insulin complex was determined in an aqueous solution by detecting the fluorometric intensity (λ
ex = 400 nm, λ
ex = 500 nm). The calibration curve for the constructed boron was linear over the range of 0 to 0.5 ppm. The limits of detection and determination for boron were 3.7 and 12 ppb, respectively. The relative standard deviation at B 20 ppb was 2.6% (
n = 6). The determination results for boron in a river reference material showed good agreement with the certified value.
View full abstract