In recent years, the requirements for separation and preconcentration
procedures have undergone numerous changes. A general trend is not only to improve
the analytical performance of microextraction techniques but also to endeavor to satisfy
the requirements of green chemistry. As a result, new modified and derived methods
have been developed. One of the most popular techniques that meet the expectations of
analysts is a dispersive liquid-liquid microextraction (DLLME). Owing to its rapidity,
low costs, simplicity of operation, high recovery, as well as low consumption of both
organic or inorganic compounds the method has been widely accepted as a
miniaturized sample preparation technique. Despite the advances mentioned, DLLME
still requires expensive and hazardous organic solvents, the use of multistep procedures
leading to high risk of analyte losses, and has low selectivity and sample clean-up
efficiency. That is why much attention has been paid to the development of green
activities such as replacing toxic organic solvents and automating extraction
techniques. In this context, a new group of solvents namely ionic liquids (ILs) has been
utilized in combination with micro extraction procedures.
ILs as molten salts are made of cations and anions. The novelty in relation to ILs is
their application as the new non-molecular class of solvents characterized by a low
melting point temperature arbitrary fixed at or below 100°C, as opposed to inorganic
salts which are solid with melting point well above 500°C (NaI, NaBr, NaCl, 661, 747,
801°C, respectively). The term IL covers inorganic as well as organic salts.
The potential of ionic liquids is based on their unique properties such as a low melting
point, a negligible vapor pressure, high thermal stability, a significant viscosity,
miscibility with water and other solvents. The ionic liquids environment is very
different from that of polar or non-polar organic solvents. Besides the non-molecular
nature of ILs, the significant advantages are their non-measurable vapor pressure at
room temperature and appreciable liquid ranges. The desired physical and chemical
properties of ILs may be controlled by selecting cation/anion combination or by
incorporating specific functional groups in the IL molecule. Consequently,
combinations of a variety of cation and anions lead to a tremendous number of ionic
liquids and that is why ILs are often referred to as designer solvents. The unique properties of ionic liquids raised growing interest of scientists and
engineers regarding an application for these compounds for the extraction purposes.
Ionic Liquids and Polymeric Ionic Liquids (PILs) have been used in a Single-Drop
Microextraction (SDM), a Liquid-Phase Microextraction (LPM), a Solid-Phase
Microextraction (SPME), a Dispersive Liquid-Liquid Microextraction (DLLME), a
Hollow Fiber-Supported Liquid Membrane Extraction (HFSLME) and in a Solid Phase
Extraction (SPE), till the present day.
The chapter presents extensive theoretical and practical information on the possible
application of ionic liquids in various separation micro extraction techniques. It was
shown that ILs might be successfully used in chemistry, medicine, environmental
research and in other areas where is a need for selective isolation and enrichment of
analytes. A systematic review has also been performed involving utilization of ILs in
DLLME for the determination of organic compounds and metals in a variety of
samples. It has been presented that the DLLME method has been successfully applied
for the extraction and determination of a broad spectrum of organic and inorganic
analytes from a variety of samples such as environmental, water, food, cosmetics, and
biological.
Keywords: Dispersive Liquid-Liquid Microextraction, Hollow Fiber-Supported
Liquid Membrane Extraction, Ionic liquids, Microextraction, Single-Drop
Microextraction, Solid-Phase Microextraction.
