Eluent to be Used for NI-424

Normally aqueous solution of aromatic organic acids (4-hydroxybenzoic acid, phthalic acid) can be used as eluent for the non-suppresser type ion chromatography. Table below shows the roles each component of the eluent plays under the recommended eluent conditions for IC NI-424:

	Eluent (1)	Eluent (2)
Main component	4-Hydroxybenzoic acid	Phthalic acid
pH adjustment	Bis-Tris *	Amino caproic acid
Separation adjustment	Phenylboronic acid (Separation of phosphoric acid ion and fluoride ion promoted.)	Phenylboronic acid (Separation of phosphoric acid ion and fluoride ion promoted.)
Other	CyDTA** (Chelating agent to wash away trace amount of metal ion from system)
Feature	Provides good peak balance, enabling measurement of even high concentration sample with good separation.	Improvement in quantitative determination of phosphoric acid ion, in particular, has been made.
Note	* Bis (2-hydroxyethyl) iminotris-(hydroxymethyl) methane
	** trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid
Adjustment of Eluent (1)	1) Measure 1.105 g of 4-hydroxybenzoic acid, 0.586 g of Bis-Tris, 0.244 g of phenylboronic acid and 1.7 mg of CyDTA into a 1 liter measuring flask. Make it up to a 1 liter solution using ion exchange water. 2) After dissolving the mixture in the water by applying ultrasonic vibration, pass the solution through a 0.45 micron membrane filter and use the filtered solution as eluent. 3) For measuring low concentration ion in particular, purification of 4-hydroxybenzoic acid is recommended as impurities contained in the reagent need to be removed. Vacant peaks for trace amounts of the impurities in the reagent could interfere with the measurement.

The time and the order for ion elution can be changed by altering the type, concentration and pH of eluent.
Effect of Eluent pH on Retention Time concerns eluent (1) and shows the effects of the pH of the eluent on the retention time of each ion. Adjust the eluent in accordance with the ion to be measured.
When alkaline eluent (more than pH 7) is used, it is necessary to prevent absorption of carbon dioxide into the eluent and resulting change in the pH of the eluent. Attach a carbon dioxide trap to the mouth of the bottle containing the eluent to prevent carbon dioxide from being absorbed into the eluent. Use of acidic eluent is normally recommended as it is stable.