ONE DROP FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF LEAD COMBINED WITH SOLVENT-EXTRACTION AFTER PRECONCENTRATION WITH CALCIUM-FLUORIDE

After microwave acid digestion of botanical standards and the coprecipitation of lead at pH > 1.0 as fluorides using calcium as a carrier, a lead pyrrolidin-1-yldithioformate complex was extracted into a small volume of chloroform. Direct nebulization of the chloroform extract into a fuel-lean air-acetylene flame gave a sensitive signal intensity. The background-corrected signal intensity obtained by nebulizing 60 mul of the extract was 4.0 fold compared with that obtained by nebulizing 100 mul of an aqueous solution. The present method was successfully applied to the determination of lead in the following botanical-certified reference materials: National Institute of Standards and Technology, Standard Reference Materials (NIST SRMs) 1571 Orchard Leaves, 1572 Citrus Leaves and 1573 Tomato Leaves. The results agreed well with the certified values (reference values: 45+/-3, 13.3+/-2.4, 6.3+/-0.3; found: 43.9+/-1.0, 13.0+/-0.1, 6.1+/-0.2 mug g-1, respectively).