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The mobile phase composition does not have to remain constant. A separation in which the mobile phase composition is changed during the separation process is described as a gradient elution. [38] [39] For example, a gradient can start at 10% methanol in water, and end at 90% methanol in water after 20 minutes.
CAD response is dependent on organic content of the mobile phase, response is higher with organic-rich mobile phases than aqueous ones. [ 16 ] [ 15 ] CAD response is quite uniform for non-volatile analytes with detection limit 1–3 ng; however, the response for ionised basic analytes can be larger than for neutral analytes.
In liquid chromatography, the mobile phase velocity is taken as the exit velocity, that is, the ratio of the flow rate in ml/second to the cross-sectional area of the ‘column-exit flow path.’ For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column.
Instantaneous phase and frequency are important concepts in signal processing that occur in the context of the representation and analysis of time-varying functions. [1] The instantaneous phase (also known as local phase or simply phase ) of a complex-valued function s ( t ), is the real-valued function:
Other salts, such as 100–300 mM sodium perchlorate, that are soluble in high-organic solvent mixtures (c. 70–90% acetonitrile), can be used to increase the mobile phase polarity to affect elution These salts are not volatile, so this technique is less useful with a mass spectrometer as the detector. Usually a gradient (to increasing amounts ...
The mobile phase consists of the sample being separated/analyzed and the solvent that moves the sample through the column. In the case of HPLC the mobile phase consists of a non-polar solvent(s) such as hexane in normal phase or a polar solvent such as methanol in reverse phase chromatography and the sample being separated. The mobile phase ...
Example of a Langmuir isotherm, for a population of binding sites having uniform affinity. In this case the vertical axis represents the amount bound per unit of stationary phase, the horizontal axis the concentration in the mobile phase. In this case, the dissociation constant is 0.5 and the capacity 10; units are arbitrary.
where is the liquid phase composition with molfraction for fluid component i, and and are the gas phase and total fluid compositions, respectively. For a non-Newtonian fluid (in the sense of a generalized Newtonian fluid ), the constitutive equation for shear viscosity is also a function of the shear velocity gradient: