Suppression of iron interference in the deter‐mination of boron using the azomethine‐H procedure

Abstract

A method is proposed for the determination of boron (B) in soil extracts, plant material digests, and concentrated hydrochloric acid (HCl) digests using the spectrophotometric azomethine‐H procedure modified by the addition of thioglycolic acid and the addition of the reagents in a specific order. The soil B was extracted using a 30 min boiling 0.01M calcium chloride (CaCl₂) + activated carbon and a 30 min shake using 0.05M HCl + activated carbon. Plant material B was extracted by dry‐ashing at 600° C and dissolving the ash in 0.18M sulfuric acid (H₂SO₄) while a superphosphate sample was digested in boiling concentrated HCl. In each case B was determined using the proposed modified azomethine‐H spectrophotometric procedure. The results showed good precision and accuracy when compared to that obtained by inductively coupled plasma emission spectro‐metry (ICP). The use of thioglycolic acid to suppress Fe interference enhancement when determining B by the azomethine‐H procedure is considered essential, especially in B‐deficient soils.