Problems with light-scattering detectors

The large and nonspecific sensitivity of light-scattering detectors (ELSD) has its pitfalls. The most common ones are the following. 

Note that the linear range of an ELSD is comparably small. If the concentrations of 

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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. 

Stolyhwo et al. (106) described a different analytical methodology, one that circumvents most of the problems encountered so far and permits the analysis of TGs up to and including tribehenin and the quantitative analysis of these complex mixtures with few calibrations, using a laser-light-scattering detector. For the achievement of most separations, a 250 X 4.0-mm ID HIBAR LICHROSPHER1000 CH-18/3 (5-/an particles) was used. For the achievement of some difficult separations, a second, similar column was connected online to the first one. 

The advent of the use of mass spectrometers as detectors and new mass detectors such as the charged aerosol detectors (CAD) and evaporative light scattering detectors (ELSD) should provide high-sensitivity detection of compounds that do not absorb UV light. The only problem with most of these is that they are expensive and, therefore, not readily available. When prices come down, they should finally eliminate the use of derivatives in HPLC analysis. 

The detection problems of the LC LC procedmes are similar to LC CC (see section 11.8.3). The zone of interacting tnacromolectrles is partially overlapped with the barrier and this fact complicates quantitative sample monitoring. This is why the evaporative light scattering detectors with all their drawbacks (see section 11.6.1.4) are so far mostly employed in the LC LC measurements. 

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. 

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