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Superior HPLC Detection

Replace or Complement Your Current Detection

SofTA Evaporative Light Scattering Detectors (ELS Detectors) are near universal detectors, primarily used in High Performance Liquid Chromatography (HPLC). ELS detectors are an ideal substitute, or supplement to, traditional HPLC detectors for liquid chromatography concentration detection.

 

An ELS detector employs a unique method of detection. The process involves three steps: nebulization, evaporation and detection.

 

Nebulization

In the first step, the SofTA ELS detector transforms the liquid phase leaving the column into an aerosol cloud of fine droplets. The size and uniformity of the droplets are extremely important in achieving sensitivity and reproducibility. SofTA ELSDs use a concentric gas nebulizer and a constant flow of an inert gas to achieve the required consistency.

 

Evaporation

The aerosol cloud is propelled through the heated evaporation tube assisted by the carrier gas. In the evaporation tube the solvent is volatilized to produce particles or droplets of pure analyte. The temperature of the drift tube is set at the temperature required to evaporate the solvent. The design of the SofTA drift tube provides evaporation of solvents at low temperatures to minimizes the evaporation of the compound of interest. Low temperature operation makes our ELS a reliable method to detect everything in the sample.

The total swept volume of the detector is critical to maintain narrow peak widths, especially important for work with small column volumes. The SofTA ELS detectors feature extremely low swept volume and minimum peak dispersion.

 

Detection

The particles emerging from the evaporation tube enter the optical cell, where the sample particles pass through a beam of light. The particles scatter the light. A light trap is located opposite the laser to collect the light not scattered by particles. The amount of light detected is proportional to the solute concentration and solute particle size distribution. SofTA ELS detectors guarantee years of stable detection by employing an laser diode light source instead of a short-lived halogen lamp. This eye-safe laser when combined with our photo-diode provides at least 3 orders of magnitude detection without changing gain or range.

 

Vapor Phase Control

To handle flow rates and mobile phases common in HPLC, all ELSDs need a way to divert part of the aerosol cloud to waste. One of the earliest successful approaches to aerosol splitting involved a nebulization chamber with a flow restriction and sharp turn. The larger particles in the cloud would fail to make the turn, hit the wall, and ultimately run out a drain. When this geometry is optimized for high flow rates or difficult to evaporate mobile phases, too much will be sent to waste under less severe operating conditions. This limits sensitivity in many processes.

 

A more recent solution to the problem is the plate impactor. Larger particles hit the plate, condense, and go out a drain. Smaller particles make it through the annular space and continue on to the evaporative zone. When less severe conditions are encountered, the plate is turned parallel to the flow, allowing all particles to pass. In this design, the impactor is either on, or off. There is no in between setting for processes which have moderate flows, or moderately difficult to evaporate mobile phases.

 

 

Ideally, an ELSD would have the ability to vary the split ratio smoothly over a wide range. This is exactly what SofTA Thermo-Split™ technology does (Patent No. US 7,290,723 B1).