Ultrasound assisted ion pair based surfactant-enhanced liquid–liquid microextraction with solidification of floating organic drop combined with flame atomic absorption spectrometry for preconcentration and determination of nickel and cobalt ions in vegetable and herb samples

In the proposed work an ultrasound assisted ion pair based surfactant-enhanced dispersive liquid–liquid microextraction (UA-IPSE-DLLME) with solidification of floating organic drop was studied for preconcentration and flame atomic absorption spectrometry (FAAS) determination of nickel and cobalt ions in vegetable and herb samples. Congo Red (CR) and didecyldimethyl ammonium chloride (DDMAC) were used as complexing and ion-pairing agents, respectively. By using ion-pairing agent CR-metal complexes gained more hydrophobic character and extracted into 1-dodecanol more efficiently. Some parameters affect extraction efficiency were studied and some analytical characteristics of the method were calculated. Under optimized conditions, detection limit of 1.7 μg L ⁻¹ and 2.4 μg L ⁻¹ , quantification limit of 5.6 μg L ⁻¹ and 7.9 μg L ⁻¹ and enrichment factors of 65 and 48 were obtained for nickel and cobalt, respectively. Relative standard deviation (n = 7) for 100 μg L ⁻¹ nickel and cobalt were 3.6% and 3.8%, respectively. The proposed UA-IPSE-DLLME method has been successfully applied for the determination of nickel and cobalt ions in certified reference materials and some food samples.