Viscosity of mobile phase

Several factors can contribute to the difference in retention times for PEO in different mobile phases the viscosity of a mobile phase, the hydrodynamic volume of a PEO, and the swelling or void volume of a column. Shodex and TSK columns should swell more in water than in water/methanol, and PEO should therefore come out later in water than in water/methanol. PEO should also elute later in water than in water/methanol because water/methanol is a better solvent for PEO than water. The viscosity of the 50 50 water/methanol mobile phase is higher than the viscosity of water. PEO should therefore elute later in water/methanol than in water due to the difference in viscosity. The results in Table 17.9 indicate that the difference in retention time for PEO in water and in water/methanol depends more on the swelling of columns and the hydrodynamic volumes of PEO than the viscosities of mobile phases. 

PRINT Enter Viscosity of Mobile Phase (Poises)" INPUT M... 

Capacity Ratio of the Last Eluted Peak "Diffusivity of Solute in Mobile Phase "Viscosity of Mobile Phase... 

PRINT Enter Separation Ratio of the Critical Pair INPUT A PRINT Enter Capacity Ratio of the First Peak of the Pair" INPUT k I PRINT Enter Capacity Ratio of the Last Eluted Peak" INPUT K2 PRINT Enter Diffusivity of Solute in Mobile Phase UNPUT D1 PRINT Enter Viscosity of Mobile Phase (Poises)".INPUT M PRINT" Enter Column Inlet Pressure (p.s i)" INPUT P PRINT BASIC CHROMATOGRAPH IC DATA"... 

PRINT"Separation Ratio of the Critical Pair",A PRINT Eapacity Ratio of the First Peak of the Pair",Kl PRINTTapacity Ratio of the Last Eluted Peak"K2 PRINT"Diffusivity of Solute in Mobile Phase Dl PRINT "Viscosity of Mobile Phase (Poises) M PRINT"Column Inlet Pressure (ps.i.TP LET N=( 16 ( 1 +KI ) 2)/(((A-1 )"2) (K 1 2))... 

Viscosity of mobile phase (mass transfer term)... 

High viscosity of mobile phase Change mobile phase, or increase column temperature. Change to lower viscosity solvent. 

High viscosity of mobile phase. —> Use solvent of lower viscosity or increase temperature. 

It is useful to know the viscosity of the solvents that can be used as mobile phases in liquid chromatography. The number of such solvents is limited, and accurate viscosity data are available for all of them. Thus, this discussion is limited to the viscosity of mobile phases used in HPLC and the predictive equations that can be used to estimate the viscosities of liquids when accurate data are not available [5] will not be covered. However, note that any liquid, whether it is a conventional solvent or not, can be used as the mobile phase provided it affords... 

Diffusion of solutes within the column is critically important in liquid chromatography. Under typical HPLC conditions, viscosity of a mobile phase and the diffusion coefficient of a solute do not vary greatly with pressure. The Stokes-Einstein equation of diffusivity of solvent shows that the relationship of an analyte diffusion coefficient (D) is inversely proportional to the viscosity of mobile phase (ti). As seen in Eq. (3.20) ... 

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