Detector mass light scattering

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. 

Detector sensitivity light scattering and viscosity detectors are very sensitive towards higher molar masses while RI detectors are most sensitive at lower molar masses,... 

Although tocopherols and tocotrienols can be detected by UV absorbance at 280 nm, fluorescence detection (excitation 294 nm and emission 326 nm), as shown in Figure 11.3, has proven to be a much more sensitive method. Electrochemical detection such as pulsed amperometric and coulometric (Uspitasari-Nienaber, 2002) has also proven to be sensitive and potentially valuable for the quantitative analysis of tocopherols and Tocotrienols (Abidi, 2000), especially for tocol analysis in blood and serum samples. HPLC mass detectors such as flame-ionization detectors, evaporative light-scattering detectors, and charged aerosol detectors have proven to be valuable for the quantitative analysis of many types of lipids, but because tocols have... 

Molecular weightjmass detectors include light scattering detectors and viscosity detectors. When SEC is used in the characterisation of polymer systems, its main aim will be the production of a molecular mass/weight distribution and where possible absolute molecular weights. Mass calibration is a complicated matter (section 9.3.5.1) in that calibration curves differ for different polymer types, and for many commercial polymers, direct molar mass calibration is not possible because of the lack of suitable, known molecular weight standards. 

Gel permeation chromatography (GPC) is the established method for the determination of molar mass averages and the molar mass distributions of polymers. GPC retention is based on the separation of macromolecules in solution by molecular sizes and, therefore, requires a molar mass calibration to transform elution time or elution volume into molar mass information. This kind of calibration is typically performed with narrow molecular mass distribution polymer standards, universal, or broad calibration methods or molar-mass-sensitive detectors like light-scattering or viscosity detectors. 

To illustrate the power of this column, an application to the separation of the fatty acids of the sea snail Rapana thomasiana is illustrated in Figure 6.3 [175]. The column was eluted with a gradient of acetonitrile into methanol, and a mass (light-scattering) detector was used (UV detection at low wavelengths would... 

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... 

At least one SEC detector is required to detect the eluting sample. The MMD is then derived from the slice information of the measured concentration, the molar mass (from a calibration curve or measured directly using additional detectors as light scattering detectors or mass spectrometers), and the slope of the calibration curve. 

These combined HDF and GPC separations require the use of detectors such as static light scattering or viscometers to help sort out the convoluted elution profiles seen in those type of experiments. It should also be remembered in these situations that the typical refractive index or ultraviolet detector responses may not be representative of the actual mass fraction of insolubles eluting from the column because of the significant light scattering that can occur with those large particles in the detector cell. 

Trathnigg, B., Kollroser, M.J. (1997). Liquid chromatography of polyethers using universal detectors V. Quantitative aspects in the analysis of low-molecular mass poly(ethylene glycols) and their derivatives by reversed-phase HPLC with an evaporative light scattering detector. J. Chromatogr. A 768, 223-238. 

Simple homopolymers, where monodisperse standards and suitable solvents are available, are easily characterized by SEC. Homopolymers for which no monodisperse standards are available additionally require some more elaborate detection system for transformation of the retention time into molecular weight. This can be done by, e.g., universal calibration. Alternatively, an absolute molar mass detector, like an on-line light scattering detector or mass spectrometer, can be used. 

Ederle and Mathis, in a very careful study, recently showed by SEC with combined mass and molecular weight (light scattering) detectors that exactly six polystyryllithium chains can be coupled with pure fullerene (C60) in toluene. Furthermore, comparison of the mass and UV (set at 320 nm sensitive to the presence of C60) traces proved the uniformity of the C60 core in the star polymer [49],... 

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