Determination of trace elements in plant materials by a dry-ashing procedure. Part I. Cobalt and molybdenum

Abstract

Dry-ashing and analytical procedures for the spectrophotometric determination of cobalt and molybdenum in ashed plant extracts are described. A two-stage ashing process using nitric acid combined with either potassium hydrogen sulphate or sulphuric acid as ashing aids and oxygen enrichment during ashing facilitated the complete oxidation of plant materials.

Modified spectrophotometric procedures were devised for the quantitative determination of cobalt and molybdenum as the 2-nitrosonaphth-1-olate and toluene-3,4-dithiolate complexes in carbon tetrachloride. The extraction, chelation and phase-separation steps simplified existing published techniques, permitted more rapid sample handling, controlled interferences more effectively and provided more accurate assays. The molar absorptivities for cobalt and molybdenum were 5.1 × 10⁴ and 2.5 × 10⁴ l mol^–1 cm^–1, respectively, and the detection limits for both elements were 4 ng g^–1.