Refractometric detector

This detection system is coupled with anion-exchange chromatography (48,49), which has the same alkaline pH requirements. The sensitivity of PAD is considerably higher than that yielded using the refractometric detector, with detection limit being of the order of 10 pmol (29). On the other hand, its response also depends heavily on the nature of the carbohydrate. Finally, other alternatives described in the literature include the use of nickel-based or copper-based electrodes and catalytic oxidation (50). 

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... 

For a common SEC system with one column of (250 to 300) mm length and (7.5 to 10) mm diameter, typical v, is (50 -100) pL and c. equals 1-5 mg.mL. c. should be decreased as M rises over 100 kg.mol , and especially over 1,000 kg.mol. Correspondingly, v. is to be increased. Generally, c. is to be raised for broad molar mass distributed samples. The latter specifications are only approximate and the actual optimum experimental conditions depend mainly on the sample detectability. For example, in the case of refractometric detector, sample detectabihty is dictated by the refractive index increment, dn/dc for the given polymer in eluent. In aity case, the c and v should be kept as low as possible. It is useful to start preliminary experiments with a higher sample concentration and to decrease it gradually down to the experimentally bearable limit, which is mainly dependent on the base line stability of chromatogram. 

Optical rotation and refractometric detectors were combined to characterize a series of dextrins by gel permeation chromatography and high performance liquid chromatography (HPLC). Gel permeation fractionates according to the hydrodynamic volume when adsorption is avoided/ and for this reason separates isomaltodextrins from linear maltodextrins. Specific rotation power [a] is directly obtained and confirms the chemical structure. Elution of cyclodextrins is also tested and discussed. HPLC reverse phase chromatography separates the anomers as shown by optical rotation and allows good resolution in the range of low DP. 

Light scattering and refractometric detectors were used to analyze starch with different amylose contents. Fractionations were also performed and iodine complexation tested in relation with the molecular structure. Gel permeation chromatography in DMSO was used to determine the molecular weight distribution of different starch samples without any calibration. 

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