Sensitive determination of cadmium in brown rice and spinach by flame atomic absorption spectrometry with solid-phase extraction

A sensitive flame atomic absorption spectrometry (FAAS) method was developed for the determination of cadmium (Cd) in brown rice and spinach. The method involves extraction with 1M hydrochloric acid (HCl), followed by a selective pre-concentration by solid-phase extraction (SPE). The pH of the loading sample solution was adjusted to 4.0 for the brown rice and to 5.0 for the spinach. The masking agents, tartrate and citrate, were required for the spinach before pH adjustment. The SPE step achieved a 20-fold enrichment of the sample solution. The limits of quantification (LOQs) were 0.0054 mg kg(-1) for the brown rice and 0.0022 mg kg(-1) for the spinach, being more sensitive than those of AOAC Official method 999.10. A single-laboratory validation was performed by testing spiked samples at 0.04 and 0.08 mg kg(-1) for the brown rice, and 0.02 and 0.04 mg kg(-1) for the spinach. The average recoveries were 93.3-96.9% with relative standard deviations (RSDs) of 4.1-8.2% for brown rice, and 90.5-91.9% with RSDs of 5.8-10.0% for spinach.