Refractometry, application

It is worth stressing that in the use of the coated LPG as a refractometer, and not as chemical sensor, the sPS layer acts just as a passive HRI layer and no chemical interaction with surrounding medium occurs. Therefore, any HRI overlay could be used for the refractometry, not necessarily a chemo-sensitive one as the sPS. However, in this work the same material has been used for both applications taking advantage of the experience ripened in its deposition. 

Some of the typical parameters or properties utilized for NIR detection are potentiometry,(5) absorbance,(52 54) refractometry/18,19) or fluorescence spectros-copy.(55) Of these, has proven to be the most valuable detection method in fiber optic applications/2,56) In standard spectroscopic techniques, the detection limits of a method are greatly determined by the instrument and by the chemical method used for the analysis. However, in OFCD research the detection limits are governed by a series of other variables including the dye, the matrix, and the instrument. By optimizing these variables, low detection limits can be obtained with this technique. 

The field of applications for optical biosensors is wide, covering clinical, industrial control processes, veterinary, food, environmental monitoring, among others [1]. For all these applications, it is desirable to have a compact sensor of high sensitivity, fast response time and which is able to perform real-time measurements. These requirements can be achieved mainly with optical sensors, due to the intrinsic nature of optical measurements that accommodate a great number of different techniques based on emission, absorption, fluorescence, refractometry or polarimetry. 

Fiber-optic applications in the chemical industry were first tried over 15 years ago with colorimetry. However, concepts related to remote spectrometry and refractometry with optical fibers are of much more recent date. In the former area, it was necessary to overcome problems due to coupling of teleconununication fibers with spectrometric analyzers for absorption [165], fluorescence [166], and Raman scattering [167]. The last area was studied at the same time as the intrinsic FOS, with the measurement of the variation in amplitude of an optical signal as a function of the refracdve index of the optical dber cladding which consists of the liquid to be measured [168]. A characteristic example is the vehicle battery acid concentration indicator [169]. 

Refractometry is a technique used to detect the concentration of binary mixtures based on differences in their refractive index. Besides concentration, it is also a simple method to quantify purity. Salinity of brine or sucrose concentrations in grapes or syrup are two typical applications. Urine-specific gravity is measured for drug diagnostics and plasma protein is assessed by refractometry in veterinary medicine. 

See also Atomic Absorption Spectrometry Flame. Atomic Emission Spectrometry Flame Photometry. Carbohydrates Starch Dietary Fiber Measured as Nonstarch Polysaccharides in Plant Foods. Chiroptical Analysis. Essential Oils. Ethanol. Food and Nutritional Analysis Antioxidants and Preservatives Contaminants. Isotope Ratio Measurements. Liquid Chromatography Food Applications. Nuclear Magnetic Resonance Spectroscopy Appiications Food. Optical Spectroscopy Refractometry and Reflectometry. Pesticides. Sampiing Theory. Vitamins Fat-Soluble Water-Soluble. Water Determination. 

See also Activation Analysis Neutron Activation. Atomic Emission Spectrometry Inductively Coupled Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma. Chemometrics and Statistics Expert Systems. Glasses. Microscopy Applications Forensic. Optical Spectroscopy Refractometry and Reflectometry. X-Ray Fluorescence and Emission Energy Dispersive X-Ray Fluorescence. 

The carbohydrates are a problematical group of compounds from the point of view of detection, having neither useable spectrophotometric or fluorescent properties. The method of choice for detection of carbohydrates in pure solution has been refractometry but interference from other compounds in body fluids and its relative insensitivity has limited its application in clinical chemistry. The development of pulsed amperometric detection at noble metal electrodes and improvements in anion-exchange columns has now made possible the separation and quantitation of most carbohydrates of interest in urine samples. As ion-exchange columns require a constant ionic concentration to achieve consistent separations, urines are first desalted with... 

Table 1 shows the refractive indices for several materials. The variation of refractive index as a function of electromagnetic radiation wavelength (dispersion spectrum) provides simultaneous information about the polarizibility and absorption properties of the sample. The rapid development of modern optical and imaging technologies such as lasers and photodiode arrays creates opportunities for application of refractometry to small analytical systems and multidimensional monitoring. 

As occurs in the refraction spectrum shown in Figure 1, the reflectivity spectrum is often relatively featureless. Thus, a first derivative technique is generally applied which enhances the structure in a conventional reflection spectrum. This enhancement technique, which allows one to empha size small pieces of information in a relatively featureless reflection spectrum, is called differential reflection spectrometry. Refractometry and differential reflection spectrometry complement each other for their respective fields of applications. 

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