Evaporative light scattering detector nebulizer

FIGURE 7.13 Schematic of an evaporative light scattering detector. The three stages are nebulization, in which column effluent is aerosolized evaporation, in which the mobile phase is vaporized and optical detection, in which the light scattering of the residual solute particles is recorded. Some detectors also include an obstacle in the flow path for droplet discrimination, which leads to a more homogenous distribution of droplet sizes. 

An evaporative light-scattering detector responds to any analyte that is significantly less volatile than the mobile phase.21 In Figure 25-22, eluate enters the detector at the top. in the nebulizer, eluate is mixed with nitrogen gas and forced through a small-bore needle to form a... 

The evaporative light scattering detector (ELSD) [47] is based on the ability of fine particulate matter of a solute to scatter light. To obtain suitable analyte particles, the column effluent is nebulized by an inert gas in the nebulizer and aerosol droplets are allowed to evaporate in the drift tube. Droplet size is related to mobile phase properties (surface tension, density, and viscosity). Usually, high solvent-to-gas flow ratio provides the best sensitivity because it produces the largest droplet diameters. 

Figure 7.4 Evaporative light scattering detector. At the outlet of the column the mobile phase is nebulized under a stream of nitrogen, by a specially atomizing device. When a compound elutes from the column, the droplets under evaporation give a suspension of fine particles. Illuminated by a laser source they scatter the light from a lamp via the Tyndall effect (what happens is comparable to the diffusion by fog through a car headlight beam). The signal detected by a photo-diode is proportional to the concentration of the compound illuminated. Irrespective of the substance, the response factors are very close. This detector is only useful for sample components that cannot be vaporized in the heated section of this detector.

The evaporative light scattering detector (ELSD) is an instrument for the non-selective detection of non-volatile analytes. The column eluate is nebulized in a stream of inert gas. The liquid droplets are then evaporated, thus producing solid particles which are passed through a laser beam. The resulting scattered light is registered by a photodiode (Fig. 6.12). 

Another evaporative on-line detector is the evaporative light-scattering detector (ELSD) (97,104-107). In the ELSD, the eluant is nebulized with an inert gas to form an aerosol. The solvent in the dispersed eluant droplets is evaporated and removed in a heated chamber. The resulting solute particles fall through a light-scattering detector. The scattered light is related to the amount of mass in the particles, which in turn corresponds to the amount of solute in the eluant. 

In the introductory Section 2.1.3, it was discussed that an important aspect of optimization can be to improve a method for its applicability in trace analysis. The nature of the mode of detection is very relevant in this case whether the applied detector is concentration proportional like the very common UV detector or mass proportional hke nebulizer-based detectors, for example, evaporative light scattering detector (ELSD) or charged aerosol detector (CAD). This textbook contains dedicated chapters on nebulizer-based or aerosol detectors (Chapter 10 on trends in detection), as well as for the coupling of LC with mass spectrometry (Chapter 1). Here, the focus is on concentration proportional detectors UV detectors (VWD, DAD), fluorescence detectors (FLD), electrochemical detectors (ECD), and refractive index (RI) detectors. 

Figure 4.6 Schematic of an evaporative light-scattering detector. Eluent and sample peaks enter the top of the cell and are nebulized. Solvent is evaporated away leaving particles of analyte sample peaks. A light is directed at the particles and scattered light is detected, amplified and measured.

Detector Evaporative Light-Scattering Detector, SEDERE Sedex-45, evaporation temperature 50°, nebulization gas nitrogen, pressure 200 kPa, flow 6 L/min, response is nonlinear but proportional to the power 1.7 of the mass and must be calibrated for each compound... 

Evaporative light scattering is gaining popularity due to its ability to detect analytes on a nonse-lective basis. Basically, this detector works by nebulizing the column effluent, forming an aerosol that is further converted into a droplet cloud for detection by light scattering. This type of detector has been applied to studies of small molecule combinatorial libraries [13,14], carbohydrates [15], and lipids [16,17]. 

Other detectors that are capable of determining the polymer concentration in the effluent are based on dielectric constant (205) and density (206-213). Mass can be determined directly with a piezoelectric quartz sensor having a sensitivity of 10 g (214). A universal mass detector, evaporative bgbt scattering Detector (ELSD) based on the formation of droplets in a nebulizer gas and detection by light scattering using a laser, has been developed and applied to GPC (215). Commercial ELSD units are available from Alltech, Varex Corp., and Polymer Laboratories. 

Other methods include a density detector utilizing a mechanical oscillator, and also an evaporative light-scattering method. In this latter method the sample is nebulized (evaporated). Each droplet that contained nonvolatile material will form a particle. This aerosol causes hght to be scattered, resulting in a method to determine the concentration of solute. 

---