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Solvent propertiesChromatographyIn chromatography the polarity, or elution strength of solvents is used as a guide in the selection of eluents. Often the elution strength is given only qualitative as an eluotropic series. Quantitative measures are elution strength (ε0) and solvent polarity (P'). The Snyder solvent polarity index (P') has the advantage that it is easily calculated for solvent mixtures. An additional advantage is that P' can be divided into three contributions, xe (interaction with ethanol - proton acceptors), xd (interaction with dioxane - proton donors) and xn (interaction with nitromethane - dipole-dipole interactions). Together P' and xe, xd and xn can be used to fine tune both elution strength and selectivity.For a solvent mixture:
P'AB=φAP'A+φBP'B
where φA and φB are the volume fractions of solvent A and B
respectively.
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