The determination of aluminium in dithionite soil extracts using a catechol violet spectrophotometric method

Abstract

Abstract A spectrophotometric method is described for the determination of aluminium in sodium dithionite extracts of soils using catechol violet (CV) at wavelength 585 nm following nitric/sulfuric acid digestion and neutralization. The detection limit is 5 mg/kg Al in soil. Evaluations undertaken were: contributions to blank value of digestion and neutralization reagents; interferences from iron; effects of storage of acid digests; and stability of sodium dithionite extracts. All digest and neutralization reagents contributed to the blank value with lowest values found for ultra‐pure neutralizing reagents. Soil extracts were stable for up to 90 days when stored at 4°C and ‐12°C. The CV method was compared with a flame AAS method using 5 sets of extracts of 25 soil samples. Analysis of variance and linear regression showed that there was no difference between the two methods. Better precision for the flame AAS than for the catechol violet method was attributed to using 3 determinations for flame AAS compa...