Dispersive liquid-liquid microextraction techniques: history, developments and applications

In early 2006, a novel form of the liquid-phase microextraction (LPME) technique named dispersive liquid–liquid microextraction (DLLME) was developed [1]. Conventional DLLME has very simple and basic principles based on the ternary component solvent systems. In this simple and fast microextraction technique, an appropriate mixture of a micro-scale volume of water-immiscible extraction solvent (hydrophobic solvent) such as carbon tetrachloride along with a few sub mL of water-miscible disperser solvent (hydrophilic solvent) such as cetone is rapidly injected into an aqueous sample containing analyte(s) by syringe. This action makes the sample solution very cloudy and turbid, which is a result of the dispersion of extraction solvent and formation of small and tiny droplets. After the formation of the cloudy solution, the surface area between the extraction solvent and the aqueous sample becomes very large, so hydrophobic analytes can easily transfer into the extractant phase and the equilibrium state is achieved quickly and therefore the extraction time is very short. This is why DLLME can provide often higher extraction efficiencies in very short time than many other microextraction techniques. In conventional DLLME, phase separation can be accelerated by centrifuging and the extraction solvent settles at the bottom of sample solution. The organic phase can be removed and subjected to final instrumental analysis. DLLME has gained a wide acceptance in the analytical chemistry field due to its advantageous extraction efficiency, low cost and simplicity [2]. DLLME is applied for extraction and preconcentration of most organic compounds (pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, flame retardants, explosives, phthalate esters, plasticizers, antioxidants, vitamins, hormones, aflatoxins, mycotoxins, halophenols, polyphenols, amines, antibiotics, drugs and etc.) and inorganic compounds (cadmium, cobalt, nickel, chromium, selenium, lead, zinc, iron, gold, silver, mercury, copper, vanadium, arsenic and etc.) in biological, environmental and food samples [3].