Selective Separation/Preconcentration Of Vitamin B₁₂ With Aqueous Two-phase System And Its Detection By Electrothermal Atomic Absorption Spectrometry

As a promising alternative to the conventional solvent extraction system, aqueous two-phase (ATP) extraction system exhibits many attractive advangtages, e.g., favorable selectivity, moderate extraction conditions, friendship to the environment and simple instrumentations. In this thesis, a new method by coupling ATP extraction and electrothermal atomic absorption spectrometry (ETAAS) detection for the quantification of trace vitamin B12in complex samples was developed.The ATP system consisted of isopropanol and (NH4)2SO4, was adopted to the selective extraction/preconcentration of vitamin B12in the presence of excessive amount of co-existing Co2+, by taking advantages of the selective separation property of the ATP system and the hydrophobicity of vitamin B12. Some important experimental parameters governing the extraction performances, i.e., the components of ATP system, extraction time and sample pH, were investigated, and also the mechanism was discussed in detail. An enrichment factor of11.8was obtained with an ATP system consisting of1.1g (NH4)2SO4and200μL isopropanol for2.0mL vitamin B12(50μg L-1). A detection limit of0.6μg L-1for vitamin B12was achieved within a linear range of2～100μg L-1along and a precision of2.8%RSD at50μg L-1by using20μL upper phase of ATP system for detection with ETAAS. Vitamin B12contenting in a variety of samples including drinks, health-care pills and bovine liver were processed and determined by using the present procedure and the spiking recoveries were between97%-104%.