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Eluotropic Series

Commonly – a nomograph might be used to find equivalent eluotropic strength between mobile phases that use different organic modifiers. The nomograph relates each solvent using a vertical line to indicate mobile phase composition (%B), which give equivalent elution strength – known as ‘isoelutropic’ mobile phase compositions.

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Solvent strength in Reverse Phase HPLC depends upon the solvent type and amount used in the mobile phase (percentage organic modifier (%B)).

It is possible to interelate the relative ‘strength’ of each of the common solvents using an Eluotropic Series. This is a table or listing of the various solvents and their relative strength on various media – for example Aluminium Oxide or Silica for Normal Phase HPLC and C18 for Reverse Phase HPLC.

Isoelutropic mobile phases produce separations in approximately the same time frame (measured using retention (capacity) factor of the last peak) – however they show altered selectivity. This can be very useful when developing or optimising separations.

You can use the slider bar on the tool above to find various isoelutropic compositions – note that the relationship yields results which are only approximately accurate to within about ±5% B