hplc

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amit_chem
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hplc

on what basis we decide to go for ion pair reagent mobile phase.what is the selection criteria.

Dr. Analytical
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Ion pairing chromatography is

Ion pairing chromatography is used to increase the retention of ionized analytes.  A compound that is ionized (i.e., has a charge), is not retained much on a reversed phase system.  The ion pairing reagent is chosen because it has a charge that is opposite from the analyte.

So, if you analyte is A-, you should choose a positively charged IP reagent (IP+).  When these two combine in the column, the neutral ion pair (A-IP+) behaves like a neutral molecule and has more retention.  Also, the IP reagent also coats the surface of the stationary phase, and creates an ion-exchange surface, which also retains the analyte by ion exchange interactions.

Positive IP reagents are usually quaternary ammonium salts (trimethyl octyl ammonium sulfate).

Negative reagents are sodium octyl sulfonate.