On‐Line Preconcentration of Cadmium in Commercial Tea Samples using Polyurethane Foam as Filter Associated with Ultrasonic Nebulization‐Inductively Coupled Plasma Optical Emission Spectrometric Detection

Abstract

Tea is the most popular beverage, next to water, consumed by over two‐thirds of the world's population. The present paper proposes an on‐line preconcentration procedure for cadmium determination in tea samples (Camellia sinensis) by ultrasonic nebulization associated with inductively coupled plasma optical emission spectrometry (USN‐ICP‐OES). It is based on the precipitation of cadmium(II) ion onto a conical minicolumn packed with polyurethane foam using 2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol (5‐Br‐PADAP) as precipitating reagent. The collected analyte precipitate was quantitatively eluted from the minicolumn with 20% (v/v) nitric acid. An enhancement factor of 240‐fold (20 for preconcentration and 12 for USN) was obtained. The detection limit (DL) value for the preconcentration of 10.0 mL of sample was 4.0 ng L−1. The precision for 10 replicate determinations at 0.1 µg L−1 cadmium levels was 3.2% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the preconcentration system for cadmium was linear with a correlation coefficient of 0.9998, at levels near the detection limits up to at least 500 µg L−1. The preconcentration procedure was successfully applied to the determination of cadmium in tea samples.