Refractive index , detection

Extensive work has been performed with refractive index (Rl) detection for ion chromatography [68-70], The refractive index detector can be considered to be a universal detector because any salt (or acid or base) added to water will cause a change in refractive index of the solvent. The differences in refractive index can be measured 

Up to the present day, a very common method that employs refractive index detection is the simultaneous analysis of main constituents of wine (ethanol, glycerol, glucose, fructose, tartrate, malate, lactate, succinate, acetate, and citrate) [168]. Based on the work of Pecina et al. [169], such separation is usually carried out on HPX-87H (Bio-Rad Laboratories, Hercules, CA, USA) with a dilute sulfuric acid eluent. However, without modifications, the method originally described by Pecina et al. is not suitable for the analysis of wine. In order to separate as many components as possible, column temperature and eluent concentration have to balanced and optimized. Retention times of many organic 

Radler [168] compared their HPLC results with those obtained by enzymatic analysis and, with few exceptions, found them in good agreement 

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The free oil can be determined by an ion exchange HPLC technique. A solution of the sample in ethyl alcohol is analysed by high-performance ion exchange chromatography using a specially prepared ion exchange resin stationary phase, ethanol mobile phase, and differential refractive index detection. 

The separation was carried out on a TSKgel Amide-80 column 4.6 mm i.d. and 25 cm long with a mobile phase consisting of a 80% acetonitrile 20% water mixture. The flow rate was 1 ml/min and the column was operated at an elevated temperature of 80°C. The saccharides shown were 1/ rhamnose, 2/ fucose, 3/ xylose, 4/ fructose, 5/ mannose, 6/ glucose, 7/ sucrose and 8/ maltose. The analysis was completed in less than 20 minutes. These types of separations including other biomonomers, dimers and polymers are frequently carried out employing refractive index detection. 

Mhatre, R. and Krull, I. S., Determination of on-line differential refractive index and molecular weight via gradient HPLC interfaced with low-angle laser light-scattering, ultraviolet, and refractive index detection, Anal. Chem., 65, 283, 1993. 

Munk, M., Refractive index detection, in A Practical Guide to HPLC Detection, Parriott, D., Ed., Academic Press, San Diego, 1993, chap. 2. 

Detectability may be a significant problem with homologous series of unsaturated compounds, particularly //-alkanes. For these compounds, refractive index detection or evaporative light-scattering, both of which are described elsewhere in the book, may be of use. Indirect photometry is a useful detection scheme for compounds that do not absorb in the UV. Acetone, methylethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, and acetophenone are added to an acetonitrile/water mobile phase, generating a negative vacancy peak when the nonchro-mophoric analyte emerges and a positive peak if the ketone is adsorbed and displaced.70 Dodecyl, tetradecyl, cetyl, and stearyl alcohols also have been derivatized with 2-(4-carboxyphenyl)-5,6-dimethylbenzimidazole and the derivatives separated on Zorbax ODS in a mobile phase of methanol and 2-propanol.71... 

Figure 21 Analytical scale separation of oligomers of a-(l,4)-linked galacturonic acid. Column 25 x 0.46 cm Dynamax NH2. (A) Gradient separation, pH 5.9, 0.1-0.4 M phosphate in 25 min. UV detection at 220 nm. (B) 0.8 M acetate, pH 5. Refractive index detection. (Reproduced with permission from Elsevier Science from Hotchkiss, Jr., A. T., Hicks, K. B., Doner, L. W., and Irwin, R L., Carb. Res., 215, 81, 1991.)...

Femia, R. E. and Weinberger, R., Determination of reducing and non-reducing carbohydrates in food products by liquid chromatography with post-column catalytic hydrolysis and derivatization comparison with refractive index detection, /. Chromatogr., 402, 127, 1987. 

Lecacheux et al.240 have examined xanthan samples from various suppliers using SEC and refractive index detection coupled with on-line LALLS (Table 5, XCPS-2). Figure 13 shows LALLS and refractive index chromatograms... 

Z. H. Hash22 reported chromatographic conditions for separating anhydroerythromycin from erythromycin using a normal phase Corasil II silica gel column, with chloroform as mobile phase and refractive index detection. 

White et al.23 devised a reverse phase high performance Tiquid chromatographic procedure for erythromycin. Refractive index detection was used since the compound absorbs weakly in the UV. 

Jakeway, S. C. de Mello, A. J., Chip based refractive index detection using a single point evanescent wave probe, Analyst 2001, 9, 1505 1510... 

Most compounds can be detected directly as they are able to produce a direct analytical signal. Photometric detection, especially UV (including diode array and multi-wavelength UV detection) is by far the most frequently applied detection technique. The application of mass spectrometry (MS) detection in CE is attractive as it can provide structural information [44]. Hologram-based refractive index detection [45] and electrochemical detection [46,47] were also reported. Conductivity [41,48-50] and amperometric [51,52] detection has shown to have advantages for the analysis of both organic and inorganic compounds. 

Other detection systems, such as conductivity detector or refractive index detection are generally applicable for the determination of common anionic surfactants [1]. However, they are less sensitive than other techniques and are used more often for the characterisation of pure surfactants, than for their determination at low concentrations. 

Although AS and AES can be detected at a low UV wavelength, sensitivity is lacking and a more suitable detection was achieved using indirect photometric detection, post-column colour formation reactions, or a pre-column derivatisation, suppressed conductivity detection and refractive index detection [1,42,43]. A comparison of detection limits for the determination of these anionic surfactants shows that photometric and conductivity detectors are better (picomole or nanogram range) than refractive index or fluorometry detectors by about a factor of 1000 [40],... 

A light beam is refracted to different extents by different compounds. This mechanism is used for refractive index detection. This detector is not sensitive and the selectivity differences are negligible for homologous compounds, but any solvent with a different refractive index to the analyte can be used as the eluent. This detector is mainly applied to size-exclusion and preparative-scale liquid chromatography. 

Fig. 2.—Preparative Separation of Same Sample as Used in Fig. 1, on Laboratory-packed, Preparative Column (2.2 x 30 cm) of HPX-42 (Ag+) Resin, Eluted with H2O at 1.1 mL/min. [Sample size, 125 mg pressure, 700 kPa. Refractive index detection at 128x. Each numbered oligosaccharide was collected at 75-92% purity. Numbers above peaks refer to d.p. values. See also. Ref. 8.]...

Research has been done showing that rapid pressnre-driven LC analysis can be done with little solvent consumption, demonstrating this as a viable process analytical tool. Using electrokinetic nanoflow pumps LC can be miniaturized to the point of being a sensor system. Developments in terms of sampling to enable sampling directly from a process stream, to the separation channel on a chip are critical for the application of miniaturized process LC. The components (valves and pumps) required for hydrodynamic flow systems appear to be a current limitation to the fnll miniatnrization of LC separations. Detection systems have also evolved with electrochemical detection and refractive index detection systems providing increased sensitivity in miniaturized systems when compared to standard UV-vis detection or fluorescence, which may require precolumn derivatization. 

As a result of advances in detection technology, newer HPLC detection techniques may be utilized. For example, evaporative light-scattering detection and refractive index detection may be used to quantify impurities with poor or no UV chromophore. Conductivity detection may also be used. In some cases, when no chromophore is present, chemical derivatization may be used to add a chromophore. Increasingly, tandem techniques such as liquid chromatography mass spectrometry (LC-MS) and GC-MS are utilized for impurity characterization. The highly selective nature of LC-MS ensures that few impurities are undetected. 

Endo, Y., Tagiri-Endo, M., Seo, H. S., and Fujimoto, K. (2001). Identification and quantification of molecular species of diacylglyceryl ether by reversed-phase high-performance liquid chromatography with refractive index detection and mass spectrometry. J. Chro-matogr. A 911, 39-45. 

Liu M, Xie C, Xu W, Lu WY. Separation of polyethylene glycols and their amino-substituted derivatives by high-performance gel filtration chromatography at low ionic strength with refractive index detection. Journal of Chromatography A 1046, 121-126, 2004. 

Golander Y Schurrath U, Luch JR. Determination of pharmaceutical compounds in animal feeds using high-performance liquid-chromatography with refractive-index detection. Journal of Pharmaceutical Sciences 77, 902-905, 1988. 

Kenmore CK, Erskine SR, Bornhop DJ. Refractive-index detection by interferometric backscat-ter in packed-capillary high-performance liquid chromatography. Journal of Chromatography A 762, 219-225, 1997. 

Deng YZ, Li BC. On-column refractive-index detection based on retroreflected beam interference for capillary electrophoresis. App/ierf Optics 37, 998-1005, 1998. 

RID refractive index detection/detector or regnlations concerning the... 

A short guard column containing the same stationary phase as the analytical column is placed before the analytical column to protect it from contamination with particles or irreversibly adsorbed solutes. A high-quality pump provides smooth solvent flow. The injection valve allows rapid, precise sample introduction. The column is best housed in an oven to maintain a reproducible temperature. Column efficiency increases at elevated temperature because the rate of mass transfer between phases is increased. Mass spectro-metric detection provides quantitative and qualitative information for each substance eluted from the column. Ultraviolet detection is most common and it can provide qualitative information if a photodiode array is used to record a full spectrum of each analyte. Refractive index detection has universal response but is not very sensitive. Evaporative light scattering responds to the mass of each... 

El. 2 HPLC of Mono- and Disaccharides Using Refractive Index Detection... 

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