The Low-Temperature Evaporative Light-Scattering Detector (LT-ELSD)
All compounds which are less volatile than the mobile phase can be detected. Detection is based on a Universal property of all analytes and does not require the presence of any chromophoric group, electroactive group, etc.
The detector response is directly related to the mass of the eluted compound. Therefore, it provides similar response factors for molecules with close structures, which is quite convenient for simplifying quantification procedures or making them possible when standards are not commercially available.
Gradient mobile phases can be used to analyse samples. A gradient can be performed to optimise the separation since the mobile phase is removed from the eluent before detection. With ELS detection, a broad range of mobile phase modifiers such as AcONH4, AcOH, HCOONH4, HCOOH, CO3NH4, TFA, HFBA, or N(C2H5)3 can be readily used to separate complex samples.
Nebulization
Nebulize Eluent and select Small Droplets
Nebulization: The Eluent from the column is mixed with an inert gas and goes through the narrow orifice of a nebulizer to generate a homogeneous mist. This fine mist comprises droplets of mobile phase containing the compound of interest.
SEDEX LT technology allows the selection of droplets based on their size to prevent larger droplets from entering the evaporation (drift) tube. Large droplets would require higher temperatures to dry and are responsible for increased background noise.
Evaporation
Evaporation of the Mobile Phase: The nebulized eluent evaporates the mobile phase through a heated drift tube.
Solute molecules are obtained from the mist using a heated evaporation (drift) tube, at a low temperature. All SEDEX detectors are designed to evaporate mobile phases with high boiling points at very low temperatures. This unique feature minimizes the potential for evaporation or thermal decomposition of the compounds of interest and makes the SEDEX LT technology a more reliable way to detect everything in the sample.
Detection
Detection: The stream of solid particles enters a flow cell, including a light source and a photomultiplier or photodiode. The intensity of the light scattered by the particles is directly related to the mass of the eluted compound.
The solute molecules from the mist, assisted by Gas-Supported Focusing (GSF), pass through an optical head designed to measure the scattered light. GSF involves the addition of gas to focus the solute particles within the optical head for enhanced detection and safety.
All SEDERE detectors feature Low-Temperature operation to ensure superb sensitivity even for semi-volatile or thermally labile compounds. These detectors can be used with conventional analytical and preparative Liquid Chromatography, as well as with U-HPLC, HTLC, µ-HPLC, GPC, Flash Chromatography, CCC, and SFC.
Low-Temperature Detection
The unique design of the SEDEX LT-ELSD Nebulization cell allows the selection of droplets based on size. Large droplets are more difficult to evaporate and are responsible for an increased noise level. In the glass nebulization cell, the largest droplets are discarded so that the temperature can be lowered without compromising the sensitivity (signal-to-noise ratio):
This diagram illustrates the selection of the droplets as a function of their size. The mist of droplets is created by the nebulizer and is composed of droplets of various sizes. The nebulization cell acts as a real Size Exclusion Selector, so that the droplets of the largest dimension (in blue on the Figure) are evacuated to the waste. Only droplets which are below a size limit are allowed to flow through the drift tube.
Most of our competitors’ ELSDs do not select droplets and require higher temperatures to reach acceptable levels of noise during the analysis, resulting in much lower sensitivities for semi-volatile and thermo-labile compounds.
Selection of the droplets is a unique feature of SEDEX LT-ELSD and provides real Low-Temperature evaporation and the best sensitivity for all compounds.
Why is Low-Temperature evaporation significant in ELS detection?
In an ELS detector, the nebulized eluent evaporates through a heated tube. The temperature of this tube is undoubtedly the most critical parameter when optimizing detection. If the temperature is too high, the sample's semi-volatile or thermally labile compounds may evaporate or decompose and will not be detected.
SEDEX detectors can evaporate solvents with high boiling points at low temperatures. For example, the SEDEX 90LT can completely evaporate a mobile phase of 100% H2O with a flow rate of 1mL/min at 32°C.
Also, our innovative design provides performance superior to that obtained from systems requiring a special low-temperature device!