Evaporative light scattering ELS detectors

HPLC coupled with an evaporative light scattering (ELS) detector has been used as an universal detection technique also valid for quantitative analysis. Alcohol ether sulfates were analyzed by this method with good results and also at very low concentrations [295]. 

A simple and efficient alternative to the traditional UV detection of amino acids and related compounds is nowadays represented by the evaporative light scattering (ELS) detector, which allows the direct chromatographic separation, with no need for preliminary derivatization. In the field of glycopeptides-based CSPs, it was applied for the first time in the chromatographic resolution of carnitine and 0-acylcarnitine enantiomers on a TE CSP [61]. The considered compounds are nonvolatile solids and gave optimal ELS response under a variety of experimental conditions (buffered and unbuffered mobile phases, flow-rates from 0.5 to 1.5 mL/min, different kind and... 

Another possibility is to use the evaporative light scattering (ELS) detector, which can be used independently of the composition or variations of the elution solvent mixture (presence of salt solutions is the only limit), however, it is not yet so diffused, even if its earlier applications date back to early 1980s. 

Some detectors are not compatible with gradient elution, such as the electrochemical detector or the refractometric detector. The latter one is a universal detector, which gives a response for almost all sample compounds, but also for the mobile phase components. The only universal detector that can be used for gradient elution is the evaporative light-scattering (ELS) detector, but it is approximately two orders of magnitude less... 

The accuracy of the breakthrough method depends on the ability to detect the surfactant in the mobile phase. A refractive index (RI) detector is most often required since MLC usable surfactants should not absorb UV light. An evaporative light scattering (ELS) detector can also be used successfiilly since most surfactants are solids at room temperature. 

Since the development of HPLC as a separation technique, considerable effort has been spent on the design and improvement of suitable detectors. The detector is perhaps the second-most important component of an HPLC system, after the column that performs the actual separation it would be pointless to perform any separation without some means of identifying the separated components. To this end, a number of analytical techniques have been employed to examine either samples taken from a fraction collector or the column effluent itself. Although many different physical principles have been examined for their potential as chromatography detectors, only four main types of detectors have obtained almost universal application, namely, ultraviolet (UV) absorbance, refractive index (RI), fluorescence, and conductivity detectors. Today, these detectors are used in about 80% of all separations. Newer varieties of detector such as the laser-induced fluorescence (LIE), electrochemical (EC), evaporative light scattering (ELS), and mass spectrometer (MS) detectors have been developed to meet the demands set by either specialized analyses or by miniaturization. 

UV detection of compounds having very low values around the nonselective wavelength of 210-220 nm is a poor choice and a much better approach is, therefore, a detector that shows less variation in response factors, e.g., refractive index (RI) detection or evaporative light scattering (ELS) detection. Examples of UV/RI and UV/ELS detection of ginkolides are given in Figures 5 and 6, respectively. 

Other widely used detectors for HPLC include refractive index (RI), fluorescence and evaporative light-scattering (ELS). The use of Rl and ELS detectors for pantothenic acid analysis in multivitamin dietary supplements has not been reported. The main reason is that the two detectors are not selective and thus cannot resolve pantothenic acid from other components existing in a multivitamin dietary supplement. Although fluorescence detection can be highly selective depending on the application, pantothenic acid does not have fluorescence excitation and emission and so fluorescence detection cannot be used for pantothenic acid analysis unless derivatization methods are applied (Pakin et al. 2004 Takahashi et al. 2009). Derivatization adds more complexity to analytical method and should not be used unless neeessary. For deteetion and quantitation of pantothenic add in multivitamin dietary supplements with HPLC/UHPLC, a highly selective detector such as MS should be the instrument of choice. 

DSC Differential scanning calorimetry ELS(D) Evaporative light scattering (detector)... 

Detection systems used for LC analysis of pesticides are UV spectrometric detection (especially diode array detection - DAD - allowing peak confirmation by means of spectra comparison), fluorescence detection (FLD), electrochemical detection (ED), evaporative light scattering detection (ELSD), and MSD. Their characteristic sensitivities can be considered to vary in the following order ELSDdetection systems mentioned above, only ELS and MS are universal detectors. 

The evaporative light-scattering detector has been shown applicable to the analysis of many surfactants. This detector has only limited tolerance for the salts usually added to the mobile phase during analysis of anionic surfactants and is not applicable in many situations. In back-flush mode, the ELS detector can be used to determine total inorganic salts, sulfonated or sulfated surfactant, and unsulfonated or unsulfated material (30). 

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