Methods for estimating Pg content in P type humic acid and for calculating ΔlogKof its Pb fraction

Abstract

Based on the assumption that P type humic acid is composed of green fraction (Pg) and brown fraction (Pb),. methods for estimating Pg content and calculatlng Δlog K of Pb by analyzing the absorption curve of P type humic acid were presented. A green fraction of P type humic acid obtained from an alpine meadow soil by gel filtration was used as the Pg standard (λmax 450, 575, and 615 nm, E 1% 290, 126, and 168). Alkaline solutions of standard Pg obeyed the Beer-Lambert law within the concentration range of 1.6 to 31 ppm. To verify the methods, Pg content in the mixed solutions of Pg and A, B, or Rp type humic acid was estimated. It was found that the recovery of Pg would be 95±14 (2S) per cent with a probability of 0.99. Also, the calculation of Δlog K of humic acid in the mixed solutions gave satisfactory results. It was distinctly shown that the shape of absorption spectra of P type humic acid did not only depend on Pg content, but also on Δlog K of Pb.