Direct determination of Cd and Pb in gel forming konjac samples by enzymatic hydrolysis assisted slurry sampling graphite furnace atomic absorption spectrometry

Konjac flour is a gel-forming edible dietary fiber used as a food and a food additive. A method of slurry sampling after an enzymatic hydrolysis pretreatment was developed for the determination of Cd and Pb in refined konjac flour, by graphite furnace atomic absorption spectrometry (GFAAS). Konjac flour, extracted from the tuber of Amorphophallus konjac, contains high amounts of konjac glucomannan (KGM). KGM is a long chain polysaccharide and easily forms a gel in aqueous solution, which inhibits direct sample introduction into the graphite furnace. After an enzymatic hydrolysis pretreatment, the KGM gel is not formed and the flour was made into slurry for GFAAS analysis. Conditions for alpha-amylase based enzymatic hydrolysis were optimized. The vaporization behavior of Cd and Pb in the slurry of hydrolysis solution was investigated thoroughly. Calibrations against aqueous standards and slurry standards were compared and good agreement has been shown. The detection limits were 3.0 ng g(-1) Cd and 27.8 ng g(-1) Pb for solid konjac flour and the characteristic masses (m(c)) were 2.0 pg Cd and 9.0 pg Pb, respectively. The method has been applied to the determination of Cd and Pb in commercial refined konjac flour.