Development of quantitative immunochromatographic kit and visual screening immunoassay strip for cadmium.

Cadmium is a highly toxic heavy metal for humans. In 2006, the Codex Alimentarius Commission set the international standard value of Cd contained in polished rice at 0.4 mg kg(-1), thus requiring the monitoring of Cd in food. We developed two types of Cd immunochromatographic kit by using anti-(Cd-EDTA) antibody. One is the quantitative Cd immunochromatographic device which can precisely measure Cd concentrations. The other is the Cd screening strip that enables visible evaluation of Cd exceeding 0.003 mg L(-1). Compared with conventional instrumental analysis methods, the immunoassay kits provide rapid, simple, and inexpensive on-site methods. For these kits, we also developed an efficient pretreatment method that can be easily administrated on-site. In this method, brown rice samples are coarsely crushed by a hand-held grinder then mixed with an enzyme solution, and Cd is extracted with HCl. The extracted solution is then purified by a newly developed Cd-selective ion exchange column. Cd concentrations measured by the quantitative Cd immunochromatographic devices correlated well with those obtained by ICP-OES (r (2) = 0.96). The Cd screening strips performed well in tests; pretreated purification solution which gave Cd concentrations exceeding 0.4 mg kg(-1) according to the Cd immunochromatographic devices gave corresponding results with the Cd screening strips with no false positives or false negatives. These results indicate that the two immunochromatographic kits are useful for on-site measurement of Cd concentrations and screening of Cd present in brown rice.