Evaporative light-scattering

Reversed-phase hplc has been used to separate PPG into its components using evaporative light scattering and uv detection of their 3,5-dinitroben2oyl derivatives. Acetonitrile—water or methanol—water mixtures effected the separation (175). Polymer glycols in PUR elastomers have been identified (176) by pyrolysis-gc. The pyrolysis was carried out at 600°C and produced a small amount of ethane, CO2, propane, and mostiy propylene, CO, and CH4. The species responsible for a musty odor present in some PUR foam was separated and identified by gc (Supelco SP-2100 capillary column)... 

FIGURE 12,3 Separation of polyester oligomers, 2 X PLgel 3 jum MIXED-E 300 X 7.5 mm, eluent THE at 1.0 ml/min, evaporative light scattering detector... 

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. 

HPLC coupled with an evaporative light scattering (ELS) detector has been used as an universal detection technique also valid for quantitative analysis. Alcohol ether sulfates were analyzed by this method with good results and also at very low concentrations [295]. 

Mengerink et al. [243] describe for the analysis of ether carboxylic acids and mixtures thereof with ethoxylated alcohols an HPLC method with the use of a evaporative light-scattering detector (ELSD). 

Coquet, A., Veuthey, J.-L., and Haerdi, W., Comparison of post-column fluorescence derivatization and evaporative light-scattering detection to analyse saccharides selectively by LC, Chromatographia, 34, 651, 1992. 

Mercier, J.-P., Chaimbault, P, Elfakir, C. and Dreux, M., Inorganic ion determination by RPLC using evaporative light scattering detection, Am. Lab. News, 31(21), 1999. 

Many different detectors are used in RPLC, including ultraviolet-visible spectrophotometers (UV-VIS), refractive index (RI) detectors, electrochemical (EC) detectors, evaporative light-scattering detectors, fluorimeters, and... 

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... 

Progress has been made in developing electrochemical methods for detection of amino acids without derivatization.74 75 Evaporative light scattering (ELSD) is also a promising detection method.76 Flow-injection analysis... 

Peterson, J. A., Lorenz, L. J., Risley, D. S., and Sandmann, B. J., Amino acid analysis of peptides using HPLC with evaporative light scattering detection, /. Liq. Chromatogr. Related Technol., 22, 1009, 1999. 

Detection is also frequently a key issue in polymer analysis, so much so that a section below is devoted to detectors. Only two detectors, the ultra-violet-visible spectrophotometer (UV-VIS) and the differential refractive index (DRI), are commonly in use as concentration-sensitive detectors in GPC. Many of the common polymer solvents absorb in the UV, so UV detection is the exception rather than the rule. Refractive index detectors have improved markedly in the last decade, but the limit of detection remains a common problem. Also, it is quite common that one component may have a positive RI response, while a second has a zero or negative response. This can be particularly problematic in co-polymer analysis. Although such problems can often be solved by changing or blending solvents, a third detector, the evaporative light-scattering detector, has found some favor. 

Figure 8 Construction of the evaporative light-scattering detector. (From Stock-well, P. B. and King, B. W., Am. Lab., 23, 19, 1991. With permission.)...

Righezza, M. and Guiochon, G., Effect of the wavelength of the laser beam on the response of an evaporative light-scattering detector, /. Liq. Chromatogr., 11, 2709, 1988. 

Schultz, R. and Engelhardt, H., The application of an evaporative light-scattering detector in polymer analysis, Chromatographia, 29, 517, 1990. 

Mourey, T. H. and Oppenheimer, L. H., Principles of operation of an evaporative light-scattering detector for liquid chromatography, Anal. Chem., 56, 2427, 1984. 

Bruns, A., Waldhoff, H., and Winkle, W., Application of HPLC with evaporative light-scattering detection in fat and carbohydrate chemistry, Chro-matographia, 27, 340, 1989. 

ELSD Evaporative light scattering detector Raleigh scattering of atomised eluent... 

DSC Differential scanning calorimetry ELS(D) Evaporative light scattering (detector)... 

Detection in 2DLC is the same as encountered in one-dimensional HPLC. A variety of detectors are presented in Table 5.2. The choice of detector is dependent on the molecule being detected, the problem being solved, and the separation mode used for the second dimension. If MS detection is utilized, then volatile buffers are typically used in the second-dimension separation. Ultraviolet detection is used for peptides, proteins, and any molecules that contain an appropriate chromophore. Evaporative light scattering detection has become popular for the analysis of polymers and surfactants that do not contain UV chromophores. Refractive index (RI) detection is generally used with size exclusion chromatography for the analysis of polymers. 

Schultz, R., Engelhardt, H. (1990). The Application of an Evaporative Light Scattering Detector in Polymer Analysis. Chromatographia 29, 517. 

FIGURE 18.4 NPLC chromatogram of Triton X-100. Conditions Supelco LC-NH2 column, 15 cm x 4.6 mm and 3 pm particles linear gradient of 80/20/0 (heptane/tetrahydrofiiran/ methanol) to 0/90/10 in 40 min at a flow rate of 1 mL/min evaporative light scattering detection. 

Mengerink, Y., De Man, H.C.J., Van der Wal, S. (1991). Use of an evaporative light scattering detector in reversed-phase high-performance liquid chromatography of oligomeric surfactants. J. Chromatogr. A 552(1-2), 593-604. 

Trathnigg, B., Kollroser, M.J. (1997). Liquid chromatography of polyethers using universal detectors V. Quantitative aspects in the analysis of low-molecular mass poly(ethylene glycols) and their derivatives by reversed-phase HPLC with an evaporative light scattering detector. J. Chromatogr. A 768, 223-238. 

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