Practical High-Performance Liquid Chromatography (Meyer/Practical High-Performance Liquid Chromatography) || Ion-Pair Chromatography

✍ Scribed by Meyer, Veronika R.

• Publisher: John Wiley & Sons, Ltd
• Year: 2010
• Tongue: English
• Weight: 163 KB
• Edition: 5
• Category: Article
• ISBN: 0470682183
• DOI: 10.1002/9780470688427.ch13

✦ Synopsis

13 Ion-Pair Chromatography

13.1 Introduction

Ion-pair chromatography represents an alternative to ion-exchange chromatography. Many problems can be solved by either method but ion-exchange is not as good for separating mixtures of acids, bases and neutral products under certain circumstances, and this is where ion-pair chromatography then comes into its own. The fact that the reversed phases described in Chapter 10 can be used as stationary phases has added to its popularity.

Ionic samples may be separated by reversed-phase chromatography, provided that they contain only weak acids or only weak bases (in addition to neutral compounds) present in undissociated form, as determined by the chosen pH; this is known as 'ion suppression'. 1 Ion-pair chromatography is an extension of this principle. An organic ionic substance is added to the mobile phase and forms an ion pair with a sample component of opposite charge. This is, in fact, a salt but its chromatographic behaviour is that of a nonionic organic molecule:

Reversed-phase chromatography can be used in this instance. For example, an alkylsulfonate is added to cationic analytes and tetrabutylammonium phosphate to anionic analytes. A sample containing both anionic and cationic components has one type 'masked' by a counter ion and the other suppressed by a suitable pH level.

1 The process cannot be used for strong acids or bases because these are dissociated over a wide pH range and extreme pH levels would be required for ion suppression. Ion chromatography as described in Chapter 14 was developed specifically for cases such as this.