Light scattering detector
A light scattering detector (ELSD, E vaporative L ight S cattering D etector) is used in liquid chromatography to detect compounds that can hardly be detected in the UV / VIS range.
The individual eluted components are atomized in a stream of inert gas . Small droplets are formed, which are then evaporated in a heating coil. This creates fine solid particles that drift through a laser . The beam is inelastically scattered by the particles , with a photodiode registering the decrease in light intensity.
The prerequisite for the mobile phase is that it is volatile; the best are eluents with a low boiling point . The volume flow is then also dependent on this; in the case of eluents with a higher boiling point (e.g. water), the volume flow should not be more than 1 ml / min (also depending on the model). If buffers are used, all components must be volatile and should only be added in small amounts. For example, ammonium acetate , ammonia , trifluoroacetic acid , acetic acid, or formic acid can be used; However, particular attention must be paid to their purity.
An inert gas must be used as the atomizer gas. Usually nitrogen is used .
The signal from the detector or the intensity is largely determined by the molar mass of the substance to be detected; not through its chemical composition. Functional groups also have little influence. Therefore, substances with similar molar masses also have similar signal strengths (with the same injection amount).
The detector is ideally suited for gradient systems as UV or refractive index properties have no influence on the baseline. Another advantage is that the substance to be detected does not have to have chromophores , as is the case with e.g. B. for detection by means of UV or fluorescence detectors is necessary.
The detection limit is usually around 5 ng per sample component.
Individual evidence
- ↑ waters: ACQUITY UPLC ELSD: Waters. Retrieved May 23, 2017 (English).