Abstract
Vortex-assisted liquid–liquid microextraction (VALLME) is a simple, rapid and economical technique which provides reliably preconcentration and trace amounts of analytes in complex matrices. The dispersion of the extraction solvent is enhanced by vortex mixing instead of dispersive solvent to reduce the volume of organic solvent required. In this dissertation, two analytical methods based on VALLME were described. Firstly, a highly sensitive liquid chromatographic method was developed for the fluorometric determination of trace amounts of linear aliphatic primary amines. Prior to extraction, amines were derivatized with naphthalene-2,3- dicarboxaldehyde (NDA) in the presence of cyanide ion (CN) and extracted by VALLME. Under the optimum conditions, the limits of detection were between 0.01 and 0.04 nM. In comparison with o-phthalaldehyde/2-mercaptoethanol derivatization, the method has much more stable fluorescent derivatives, higher fluorescence intensities, and greater extraction efficiencies. The sensitivity enhancement factors (SEF) were between 2 and 70, which were in good agreement with the theoretical values calculated from partition coefficients in VALLME system. Secondly, a VALLME method was developed for the chromatographic determination of strontium. In the method, strontium was complexed with 4',4"(5")-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) in the presence of tetraphenylborate (TPB) as counter anion, which increased the hydrophobicity of the ion-association complex, resulting in its improved extraction into 1-octanol. Under the optimum conditions, the detection limit for strontium was 5 μg L-1 and the enrichment factor (EF) was 5.2. Moreover, SPE combined with VALLME was developed to increase the sensitivity of detecting strontium. In this method, strontium was adsorbed from a large volume of aqueous sample (100 mL) into 524 mg Sr∙SpecTM resin. The Sr was collected by deionized water and evaporated to dryness with repeated additions of deionized water to remove nitric acid and resuspended in small volumes of deionized water to give the Sr-rich extract. Under optium conditions, the EF valuse was increased to 51. Afterward, VALLME technique was performed on the obtained solution. Proposed methods were applied to the determination of trace aliphatic amines and strontium in different aqueous samples such as seawater, lake, tap and bottled water.