Chromatography refractive index detectors

Thin-layer chromatography (TLC) is used both for characterization of alcohol sulfates and alcohol ether sulfates and for their analysis in mixtures. This technique, combined with the use of scanning densitometers, is a quantitative analytical method. TLC is preferred to HPLC in this case as anionic surfactants do not contain strong chromophores and the refractive index detector is of low sensitivity and not suitable for gradient elution. A recent development in HPLC detector technology, the evaporative light-scattering detector, will probably overcome these sensitivity problems. 

The normalization method is the easiest and most straightforward to use but, unfortunately, it is also the least likely to be appropriate for most LC analyses. To be applicable, the detector must have the same response to all the components of the sample. An exceptional example, where the normalization procedure is frequently used, is in the analysis of polymers by exclusion chromatography using the refractive index detector. The refractive index of a specific polymer is a constant for all polymers of that type having more than 6 monomer units. Under these conditions normalization is the obvious quantitative method to use. 

Adsorption chromatography using small particle silica or alumina has also been employed in the separation of biologically meaningful substances. Phospholipids, for example, have been separated on silica (38). One of the big problems for such substances is detection, since many of the compounds are not U.V. active. Generally, the refractive index detector is employed for isocratic operation, and the moving wire detector for gradient operation. Formation of U.V.-active derivatives is also possible (39). 

Detection requirements in preparative-scale chromatography also differ from analytical erations where detectors are selected for their sensitivity. Sensitivity is not of overriding importance in preparative-scale chromatography the ability to accommodate large column flow rates and a wide linear response range are more useful. The sensitivity of the refractive index detector is usually quite adequate for prqtaratlve work but the ... 

Munk, M., Refractive index detectors, in Liquid Chromatography Detectors, Vol. 23, Vickrey, T. M., Ed., Marcel Dekker, New York, 1983, chap. 5. 

Gel permeation chromatography was performed in tetrahydrofuran using a Waters pump system and a Model 410 differential refractive index detector for the eluant. Five Ultrastyragel columns with nominal porosities ranging from 500 to 105 angstroms were used for all the samples and the polystyrene standards. 

There are many HPLC detectors that can turn the presence of your compound into an electrical signal to be written on a chart recorder. Time was the refractive index detector was common. Clean eluent, used as a reference, went through one side of the detector, and the eluent with the samples went through the other side. A difference in the refractive index between the sample and reference caused an electrical signal to be generated and sent to a chart recorder. If you ve read the section on gas chromatography and looked ahead at infrared, you shouldn t be surprised to find both a sample and a reference. I did tell you the reference/sample pair is common in instrumentation. 

The determination of the molecular weight of nanoparticles is performed by gel permeation chromatography (GPC). The experimental setup consists of a high performance liquid chromatography system with a size exclusion column and a refractive index detector. The nanoparticles are usually freeze-dried and dissolved in tetrahydrofuran for analysis on the system. Poly(styrene) or poly(methylmethacrylate) standards are used to calibrate the column, to enable the determination of number average molecular weight (Mn), as in... 

Separation and quantitation of carbohydrate mixtures may be achieved using HPLC, a method that does not necessitate the formation of a volatile derivative as in GLC. Both partition and ion-exchange techniques have been used with either ultraviolet or refractive index detectors. Partition chromatography is usually performed in the reverse phase mode using a chemically bonded stationary phase and acetonitrile (80 20) in 0.1 mol U1 acetic acid as the mobile phase. Anion- and cation-exchange resins have both been used. Carbohydrates... 

Infrared spectra were recorded on a Perkin Elmer Model 567 Spectrophotometer. Ultraviolet spectra were obtained on a Cary 1756 Spectrophotometer. Gas chromatograms were recorded on a Tracor Model 220 with electron capture detector. High pressure liquid chromatography studies were conducted with a Waters Model ALC-200 with ultraviolet and refractive index detectors. 

Figure 4.22 High temperature size-exclusion liquid chromatography of an engineering plastic, poly (phenyl sulfate). Column, SSC GPS-3506, 50 cm x 8 mm i.d. eluent, 1-chloronaphthalene flow rate, 1.0 ml min-1 column temperature, 210 °C detector, refractive index detector.

Experimental Techniques. Chromatography was performed on a Varian model 5060 HPLC equipped with a RI-3 refractive index detector. A Vista Plus Gel Permeation Chromatography (GPC) data system was used consisting of a Vista 401 chromatography data system serially connected to an Apple II microcomputer. The Vista 401 performs data acquisition and allows data storage and automations capability while all SEC data processing is performed on the Apple II by means of user-interactive GPC software for automated, on-line calibration and polymer analysis. 

Refractive Index Detector (Knauer). The KMX-6 scattering intensity was measured with the 6-7 degree forward-scattering annulus. A series of Zorbax PSM columns (DuPont) was used PSM 60, PSM 1000, PSM 1000, PSM 60, PSM 1000. Tetrahydrofuran (THF) from Baker was filtered through a 0.22 micrometer Fluoropore filter (Millipore Corp.) before use in chromatography, and a flow rate of 0.7 ml/min was used. 

Practice for Refractive Index Detectors Used in Liquid Chromatography, Annual Book of ASTM Standards, Vol. 14.02, E 1030-95, 1999. 

While lactose may be determined by gas liquid chromatography, high performance liquid chromatography (HPLC), using a refractive index detector, is now usually used. 

Yeung, E.S. 1986. Refractive index detector, in Detectors for Liquid Chromatography, E.S. Yeung (ed.), John Wiley Sons, Inc., New York, pp. 1-28. 

High-performance liquid chromatography (HPLC) system with refractive index detector and HPLC column (e.g., Aminex HPX-87H, Bio-Rad) fitted with suitable guard column... 

Another point of interest was the time required to equilibrate the system after changes were made in solvent composition. While the ChromSpher Lipids column had a column volume of ca. 3 ml, an increase in ACN concentration was not noted until the introduction of 7-8 ml of solvent (determined with refractive index detector). The problem of ACN-silver ion interaction and subsequent ACN retention is not new and may be noted in all forms of chromatography employing silver ions in the stationary phase. In the isocratic system, the column was equilibrated with the appropriate solvent mix for at least 0.5 h before sample injection. Since ACN dissolves very slowly into hexane, the ACN-hexane solvent mix was thoroughly stirred for 5 min before use. To obtain reproducible retention times, thorough mixing of the ACN and hexane is essential. 

Castane (31) suggests a method that is an alternative both to the enzymatic one and to gas chromatography. He uses a column, sulfonated styrene divinylbenzene resin in H+ form (Fast-Fruit Juice), 7 fim, 7.8 X 150 mm and a refractive index detector. The mobile phase, composed of H2S04 0.002 M, is maintained at 60°C. In this way he succeeds in separating and quantifying the ethanol in concentrations between 0 and 1% (v/v). The author also ascertains a reproducibility of 0.04% v/v and a repeatability of 0.07% v/v with a precision value of 0.55% v/v. 

A number of refractive-index detectors are produced for liquid chromatography. Most manufacturers of liquid chromatographs provide these detectors as standard equipment. However, the suitability of this detector for trace analysis has not been proven as yet, mainly because of the lack of sensitivity (in the jug range), and the discussion of this detector will be brief. 

Fig. 4.3. High performance liquid chromatography (HPLC) of the monosaccharides obtained from a partially purified preparation of microbubble glycopeptide surfactant from forest soil. Following hydrolysis (in 2 N HC1 for 6 hr at 100°C) and filtration, the carbohydrate mixture was charged on a Bio-Rad HPX-87 cation exchange column. For comparison, part A shows the chromatogram (using the same HPLC column) of a standard solution, which contained 4 pg of each of three different monosaccharides (i.e., the last three peaks shown are glucose, xylose and fiicose, in the order of increasing retention times). Part B shows the chromatogram obtained from hydrolysis of the partially purified (see text) microbubble surfactant (approximately 30 pg). All other experimental conditions were identical in the two cases, i.e., water eluent, 0.5 ml/min flow rate, 85°C, refractive index detector attenuation -2x. (Taken from ref. 322.)...

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