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Ion Pair Reagents

The use of ion pair reagents as mobile phase additives extends the applicability of reversed phase HPLC. Ionic or highly polar compounds are difficult to analyze by reversed phase using only organic solvent and buffer solution because of the short retention time. Ion pair reagents are strong hydrophobic ions which form neutral ion pairs with oppositely charged samples molecules, making the efficient ODS columns amenable to separate ionic or highly polar samples.

Nacalai offers a broad range of ion pair reagents for pharmaceutical compounds and other highly polar materials.

When using ion pair regents, ample time should be allowed for establishing equilibrium and for cleaning the column. When using ion pair regents with an alkyl chain of C10 or shorter, it typically takes 20 minutes for establishing equilibrium and 30 minutes for cleaning. It may take more than 1 hour to clean the column when using ion pair reagents with an alkyl chain longer than C10. Therefore, it is highly recommended to prepare a column for exclusive use with ion pair reagents.

General use of ion pair reagents in the mobile phase

ion pair flow chart

Good peak separations but retention time is too long or too short. Too long: increase organic solvent concentration by 10%.
Too short: decrease organic solvent concentration by 10%.
Good retention time, but peaks are not sharply separated. Use ion pair with longer alkyl chain, or the same ion pair using double the concentration.
No difference in separation when using ion pair, or no change occurs when trying the above solution. For basic compounds, decrease pH. For acidic compounds, increase pH.
Retention time of the sample compound is too long. Use ion pair of shorter alkyl chain or same ion pair of half concentration.


What should I pay attention to when using ion-pairing reagents?
  • Concentration of ion-pairing reagent should be 5-10 mmol/l.
  • Use mobile phase of pH 7 for acidic ion-pairing reagents and pH 2.5 for basic ion-pairing reagents.
  • Thoroughly equilibrate column before use.


  1. Higher ion pair concentration will result in longer retention time.
  2. Adjust pH of mobile phase so that the sample is well ionized.
  3. Longer equilibration time is necessary compared to mobile phases without ion-pairing reagents.
  4. Use a column exclusively for ion-pairing reagents, as it is difficult to eliminate them from the column.


Ordering Information

for Acid samples
Product Cat.No. CAS No. Purity Storage PKG Size Price(US$)  
Tetra-n-butylammonium Bromide 32824-72 1643-19-2 2-8°C 25 g 37.00 Buy
Tetra-n-butylammonium Chloride 32935-64 1112-67-0 95.00% 2-8°C 5 g 76.00 Buy
Tetra-n-butylammonium Chloride 32935-22 1112-67-0 95.00% 2-8°C 25 g 198.00 Buy
Tetra-n-butylammonium Hydrogensulfate 32924-62 98.00% RT 25 g 30.00 Buy
Tetra-n-butylammonium Iodide 32905-54 311-28-4 98.00% 2-8°C 5 g 24.00 Buy
Tetra-n-butylammonium Iodide 32905-12 311-28-4 98.00% 2-8°C 25 g 58.00 Buy
Tetra-n-butylammonium Phosphate 32929-54 5574-97-0 98.0-105.0% 2-8°C 5 g 356.00 Buy
Tetra-n-butylammonium Phosphate (0.5M solution) 32926-26 5574-97-0 RT 10 ml 44.00 Buy
Tetra-n-butylammonium Phosphate (0.5M solution) 32926-84 5574-97-0 RT 5 x 10 ml 153.00 Buy
for Basic samples
Product Cat.No. CAS No. Purity Storage PKG Size Price(US$)  
Sodium 1-Butanesulfonate (0.5M solution) 31332-84 2386-54-1 RT 5 x 10 ml 147.00 Buy
Sodium 1-Pentanesulfonate 31730-64 22767-49-3 98.00% RT 5 g 31.00 Buy
Sodium 1-Pentanesulfonate 31730-22 22767-49-3 98.00% RT 25 g 73.00 Buy
Sodium 1-Hexanesulfonate 31529-24 2832-45-3 98.00% RT 5 g 32.00 Buy
Sodium 1-Hexanesulfonate 31529-82 2832-45-3 98.00% RT 25 g 90.00 Buy
Sodium 1-Heptanesulfonate 31528-34 22767-50-6 98.00% RT 5 g 30.00 Buy
Sodium 1-Heptanesulfonate 31528-92 22767-50-6 98.00% RT 25 g 84.00 Buy
Sodium 1-Octanesulfonate 31729-04 5324-84-5 RT 5 g 32.00 Buy
Sodium 1-Octanesulfonate 31729-62 5324-84-5 RT 25 g 97.00 Buy
Sodium 1-Nonanesulfonate 31626-44 35192-74-6 98.00% RT 5 g 74.00 Buy
Sodium 1-Decanesulfonate 31429-34 13419-61-9 98.00% RT 5 g 73.00 Buy
Sodium 1-Decanesulfonate 31429-92 13419-61-9 98.00% RT 25 g 251.00 Buy
Sodium 1-Dodecanesulfonate 31426-64 2386-53-0 98.00% RT 5 g 150.00 Buy