The Low-Temperature Evaporative Light-Scattering Detector (LT-ELSD)

Basically 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 and this is quite convenient to simplify quantification procedures or to make them possible when standards are not commercially available.

Gradient mobile phases can be used to analyze samples. Since the mobile phase is removed from the eluent before detection, a gradient can be performed to optimize the separation. 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.

Step 1: 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 is composed of droplets of mobile phase containing the compound of interest.

SEDEX LT technology allows the selection of droplets as a function of their size in order to prevent larger droplets from entering the evaporation (drift) tube. Large droplets would require higher temperatures to be dried and are responsible for increased background noise.

Step 2: Evaporation
Evaporate at Low Temperature
Evaporation of the Mobile Phase: The nebulized eluent goes through a heated drift tube to evaporate the mobile phase.

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.

Step 3: Detection
Detect Scattered Light
Detection: The stream of solid particles enters a flow cell which includes a light source and a photomultiplier or a 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), go 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 that the superb sensitivity is provided 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.

Why Low-Temperature evaporation is important in ELS detection?
In an ELS detector, the nebulized eluent is evaporated by going through a heated tube. The temperature of this tube is undoubtedly the most critical parameter when optimizing detection. If the temperature is too high, semi-volatile or thermally labile compounds in the sample may evaporate or decompose and will not be detected.

SEDEX detectors can evaporate solvents with high boiling points at low temperatures. As an example, the SEDEX 90LT can completely evaporate a mobile phase composed of 100% H2O with a flow rate of 1mL/min at 32°C.

Also, our innovative design provides performance that is superior to that obtained from systems which require a special low temperature device!

Low-Temperature detection
The unique design of SEDEX LT-ELSD Nebulization cell allows the selection of the droplets as a function of the size. Large droplets, which are more difficult to evaporate, are responsible for an increased noise level. In the glass nebulization cell, the largest droplets are simply 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 the 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 largest dimension (in blue on 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 the real Low-Temperature evaporation, and the best sensitivity for all compounds.

SEDERE SAS Downloads

Sedex LT-ELSD - Model 85LT - The Standard - Low Temperature Evaporative Light Scattering Detector - Datasheet

Sedex LT-ELSD - Model 100LT - The Ultimate 2.0 - Low-Temperature Evaporative Light-Scattering Detector - Datasheet

Sedex LT-ELSD - Model 80LT - The Cost-Effective - Low Temperature Evaporative Light Scattering Detector System - Datasheet

Sedex LT-ELSD - Model 90LT - The Ultimate - Low-Temperature Evaporative Light-Scattering Detection System - Datasheet

Sedex LT-ELSD - Model LC - Low Temperature Evaporative Light Scattering Detector System - Brochure

Sedex LT-ELSD - Model FP - Chromatography Purification Mate System - Datasheet