ABSTRACT
INTRODUCTION: The World Health Organization (WHO) recommends that medicinal plants should be checked for the presence of heavy metals. A preconcentration and separation technique for trace amounts of heavy metals from plant matrix is necessary in order to increase the sensitivity and precision of their determination. OBJECTIVE: Lead, chromium and cadmium contaminations in herbal medicines were monitored using ultrasound-assisted emulsification microextraction (USAEME) combined with graphite furnace atomic absorption spectrometry (GF-AAS). METHODS: In this work, the metal ions in the aqueous solution were complexed with ammonium pyrrolidine dithiocarbamate (APDC) and were extracted into 45 µL of toluene that was sonically dispersed in the aqueous phase. The emulsion formed was centrifuged and 20 µL of separated toluene was injected into a GF-AAS for analysis. Several factors including the kind of extraction solvent and its volume, sample pH, ionic strength and concentration of APDC were optimised. RESULTS: The linear dynamic range (LDR) values were in the range of 0.05 to 20 µg/L and the limit of detection values were in the range of 0.002-0.03 µg/L for target heavy metals. Enrichment factors were obtained in the range of 70-500. The precision of the proposed method was ≤ 8% (n = 5). The obtained amounts of Pb, Cr and Cd in selected herbal medicines were in the standard range, according to the WHO reports. CONCLUSION: The USAEME with GF-AAS procedure was shown to be an efficient, rapid, inexpensive and eco-friendly method for the determination of lead, chromium and cadmium in herbal medicines. Application of the USAEME method leads to an increased extraction efficiency with satisfactory precision in a short time using an extraction solvent volume at the microlitre level.