Liquid chromatography optical sensors

The extreme sensitivity of the visible absorption spectrum to small changes in the surrounding medium has made this betaine dye a useful molecular probe in the study of micellar systems [298, 299, 443-445], mieroemulsions and phospholipid bilayers [299], model liquid membranes [300], polymers [301, 446], organic-inorganie polymer hybrids [447], sol-gel matrices [448], surfaee polarities [449-451], and the retention behaviour in reversed-phase liquid chromatography [302]. Using polymer membranes with embedded betaine dyes, even an optical alcohol sensor has been developed [452]. 

After reviewing the properties and structure of ionic liquids, leading specialists explore the role of these materials in optical, electrochemical, and biochemical sensor technology. The book then examines ionic liquids in gas, liquid, and countercurrent chromatography, along with their use as electrolyte additives in capillary electrophoresis. It also discusses gas solubilities and measurement techniques, liquid-liquid extraction, and the separation of metal ions. The final chapters cover molecular, Raman, nuclear magnetic resonance, and mass spectroscopies. 

Due to the important role of chirality in liquid crystals, a large number and variety of chiral chemical compounds have been developed. This chapter describes the most important molecular fragments and classes of chemical structures (Section 4.2) which provide both chirality and mesogenic properties. The form of chiral phases depends on the principles of the mesophase formation (Section 4.3). Some relations between the molecular chirality and the appearance of mesophase chirality are discussed and chiral dopants are classified (Section 4.4). With respect to the mesophase behavior and to optical and electro-optical applications, it is important to know how the mesogenic chirality can be modified, e.g., chemically by photoisomerization, or by changes of temperature or composition for certain suitable compounds (Section 4.5). Finally, chiral liquid crystals provide not only optical and electro-optical applications but also applications in Chemistry, e.g., as chiral solvents for synthesis, chiral stationary phases in chromatography, or chemical sensors (Section 4.6). 

Chemical sensors respond to measurands through various chemicals and chemical reactions. They have the ability to identify and quantify liquid or gaseous chemical species. This class of sensors is currently used in many chemical analysis techniques, such as mass spectroscopy, chromatography, infrared technology and others (Fraden, 2010), due to the miniaturization of sensors. There are a variety of chemical sensors with various methods of transduction. The transduction methods of chemical sensors can be organized into three classes based on their modes of measurement (i) electrical and electrochemical properties, (ii) changes in the physical properties, and (iii) optical absorption of the chemical analytes to be measured. 

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