Evaporative Light Scattering Detector ELSD

Refractive index detection allows an extremely wide latitude in the selection of the eluent type, eluent pH and the ionic strength. In principle, refractive index detection can be substituted for conductance or UV absorption detection in many separations. However, in early work, refractive index detection was found to be only moderately sensitive and was considered to be somewhat interference-prone [73]. Minimum detectable quantities for common anions such as chloride, nitrate, or sulfate were reported to be in the 20 ng to 50 ng range (compared with 1 to 5 ng for direct conductance detection). 

The stability of RI detection has improved dramatically, and it should be considered seriously as an option for rugged, sensitive detection. This is due, at least partly, to control of the cell temperature, improved electronics and improved optical transducers. The new detectors are much less sensitive to variations in room temperature. 

The highest sensitivity levels can be reached only with careful control of the chromatographic temperature. Therefore, column ovens should be considered when using RI. 

The evaporative light scattering detector works by measuring the light scattered from the particles remaining after the eluent solvent has been nebuhzed and evaporated. The eluent solvent enters the detector and is evaporated in a heated device. As chromatographic peaks are eluted from the column and enter the detector the solvent is evaporated away. Conditions are selected so that the sample peak molecules become particulate. These particles enter a chamber into which a 

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Mengerink et al. [243] describe for the analysis of ether carboxylic acids and mixtures thereof with ethoxylated alcohols an HPLC method with the use of a evaporative light-scattering detector (ELSD). 

The evaporative light scattering detector (ELSD) may have a role in this field. The response is highly dependent upon the size of analyte particles formed during evaporation of the mobile phase in the interface with the HPLC. Hence, it is hard to predict how sensitive it will be for a specific compound. Furthermore, volatile... 

Viinanen and Hopia (145) described an evaporative light-scattering detector (ELSD) that can be used to detect autoxidation products of TAG standards [trilinolenin (TLn), trilinolein (TL), and triolein (TO)] and of a natural mixture of rapeseed oil (RSO) TAGs. The samples were oxidized at 40°C in the dark in open 10-ml test tubes. Sample aliquots of 500 mg were taken for... 

Fig. 45 Reversed-phase HPLC of autoxidized trilinolenin (peroxide value = 236.4 meq/kg). Nova-Pak C18 cartridge column (Waters, Milford, MA) (3.9 X 150 mm, 60 A, 4 yam), mobile phase acetonitrile/ dichloromethane/methanol (80 10 10). Ultraviolet (UV) detector (235 nm) and evaporative light-scattering detector (ELSD). Primary oxidation products, double peak at 3.6 min secondary oxidation products elute before primary oxidation products.

Hopia AI, Ollilainen VM. Comparison of the evaporative light scattering detector (ELSD) and refractive index detector (RID) in lipid analysis. J Liq Chromatogr 1993 16 2469-2482. 

Analysis of Tween 80 was performed using a Hewlett Packard 1100 series HPLC equipped with a Sedex 55 Evaporative Light Scattering Detector (ELSD). The mobile phase consisted of 80% acetonitrile and 20% water. Duplicate injections (5 pL) of each sample were evaluated by HPLC. Potassium iodide, used for the 1-D column and 2-D box tracer studies, was analyzed with a continuous flow Isco V4 variable UV wavelength absorbance detector equipped with an EZChrom Chromatography data acquisition system. 

The advent of the use of mass spectrometers as detectors and new mass detectors such as the charged aerosol detectors (CAD) and evaporative light scattering detectors (ELSD) should provide high-sensitivity detection of compounds that do not absorb UV light. The only problem with most of these is that they are expensive and, therefore, not readily available. When prices come down, they should finally eliminate the use of derivatives in HPLC analysis. 

Some compounds are transparent and undetected by UV and FL detectors. They may be present in tiny enough quantities to be undetected by RI detectors. Evaporative light scattering detectors (ELSD) and charged aerosol detectors (CAD) can see almost any compound with good sensitivity. Mass spectrometric detectors (MSD) also can see almost any compound at high sensitivity and can also determine its molecular weight. 

Current IPC detectors are on-stream monitors. HPLC detectors range from (1) non selective or universal (bulk property detectors such as the refractive index (RI) detector), characterized by limited sensitivity, (2) selective (discriminating solute property detectors such as UV-Vis detectors) to (3) specific (specific solute property detectors such as fluorescence detectors). Traditional detection techniques are based on analyte architecture that gives rise to high absorbance, fluorescence, or electrochemical activity. Mass spectrometry (MS) and evaporative light scattering detectors (ELSDs), can be considered universal types in their own right... 

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. 

Additional detection techniques that can be employed to help solve mass balance issues with RP-HPLC are MS [30], chemiluminescent nitrogen-specihc detector [31], evaporative light-scattering detector, ELSD [32], and corona charged aerosol detection [CAD] [33],... 

Other detectors such as Evaporative Light Scattering Detector (ELSD) are also used in situations where the target compound class is known to have a weak or no chromophore. 

If no derivatization takes place, detection is preferably accomplished by UV at a low wavelength (200-210 nm) in order to enhance detection sensitivity. However, detection selectivity is sacrificed at such low wavelengths. Electrochemical detection, when applied to the analysis of free amino acids, offers higher selectivity but suffers from a small linearity range. Furthermore, most amino acids (with the exception of tryptophan, tyrosine, and cysteine) are not intrinsically electrochemically active within the current useful potential range [5]. Lately, the development of the evaporative light-scattering detector (ELSD) offers an attractive alternative for the determination of nonderivatized amino acids (see Fig. 1). 

The evaporative light-scattering detector (ELSD) was originally developed for use with high-performance liquid chromatography (HPLC) to detect nonvolatile compounds by mass rather than ultraviolet (UV) absorbance detection [1], The response is dependent on the light scattered from particles of the solute remaining after the mobile phase has evaporated and is proportional to the total amount of the solute. Because no chromophore is necessary, a response can be measured for any solute less volatile than the mobile phase. 

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