The general term ‘ion chromatography’ covers all ionic chromatographic separation methods; ‘ion-pair chromatography (IPC)‘, however, describes a very specific technique within this group that is concerned with the separation of more difficult and larger ions such as organic and inorganic ions, ionogenic, neutral and zwitterionic compounds. Conventional HPLC hardware is employed, but the mobile phase contains an ionic reagent. It is this ionic reagent that pairs with the sample ion of opposing charge. Separation is then based on the retention of the newly formed ion pairs by the solid stationary phase.
‘Ion-Pair Chromatography and Related Techniques‘, published in 2009 as part of the Analytical Chemistry Series by CRC Press (Taylor & Francis Group), is 200 pages long and costs approximately UK£80 for the hardback version. The book contains approximately 20 figures and graphs in black and white or grayscale. The author, Dr Teresa Cecchi, is based at the National Institute for Industrial Technology (ITIS) in Montani, Italy and also teaches as a professor in the Science and Technology Faculty of Camerino University, Italy. She has an extensive research background in analytical and food chemistry with a focus on ion-pair chromatography.
The book is aimed at a wider readership ranging from novices to experts within the field of IPC. It is divided into 17 chapters, roughly covering three areas:
A detailed treatise of the scientific concept of IPC;
Practical conditions for IPC separations;
An overview of applications in various research fields together with a future outlook.
Each chapter ends with an extensive list of references for further reading.
After a basic overview of chromatography and IPC in Chapter 1, the concept and theory of ion pairing, together with detection methods are described in Chapter 2. Chapters 3 and 4 focus on modeling of retention as a function of mobile-phase composition and as a function of analyte nature. Each concept is explained in great depth with the use of the relevant mathematical equations, thus providing a very thorough theoretical background for the later sections of the book. This level of depth, however, may overwhelm less advanced or less mathematically adept readers, who may have benefited from some conceptual schematics and a more general synopsis of the challenging areas of the technique.
In Chapters 5–12, the various practical conditions associated with IPC are covered. These include a discussion of stationary phases and developments in column technology in Chapters 5 and 6. Chapters 7–10 deal with aspects of adjusting mobile-phase parameters, including choice of ion-pair reagent, organic modifiers, effects of pH and influence of temperature on IPC separations. Chapter 11 is concerned with more specialized IPC modes. Finally, detection techniques and hyphenation of ICP are elucidated in Chapter 12. The concepts introduced in this middle section are nicely supported by informative tables and relevant physical equations and plots. However, the legends accompanying the plots are often difficult to read owing to small symbol size and missing characters, such as the missing micro (µ) prefix. The patterns provided in the legends for the black and white pie charts are also challenging to match to the charts themselves. A more uniform look and a better use of grayscale or color may be beneficial for a second edition.
The final section of the book is formed by Chapters 13–17. Applications of IPC within various scientific disciplines are outlined in Chapter 13, including inorganic and organic metallic species, analytes from food sciences, life sciences and medicine, as well as pharmaceutical and environmental sciences and, finally, enantiomeric separations. In Chapter 14, IPC is compared and contrasted to other separation techniques. Ion-pairing techniques are not only employed in connection with HPLC, but also with other analytical methods, such as CE, UV/visible spectrometry and analyte extraction. These are discussed in Chapters 15 and 16. Finally, in Chapter 17, the topics covered in the book are summarized and future research trends specified. These final chapters are more applied and again supported by many original research papers from the scientific literature. They help to put the previously detailed scientific theories into perspective from a practical point of view. In comparison with the previous sections, these application and conclusion chapters are rather short with less than 20 pages in total.
The subject of IPC has been covered and discussed in other ion chromatography texts, but only as a subsection or chapter. This is the first full text for over 20 years that specializes in IPC. The book provides the reader with a wealth of information on all aspects of IPC from fundamental theory, through to the numerous applications. Its style is akin to a scientific review article with many references cited at the end of each chapter, making the book a valuable resource for scientists who want to engage with the technique at a deep level. The book will be most suited to experienced researchers with a sound knowledge of separation techniques and less suited to students as a textbook to support learning on analytical separation techniques. The use of technical language requiring sound background knowledge is particularly prominent in Chapters 2–12, whereas the final section of the book is written in a more generally accessible style. On a critical note, there are very few example chromatograms; instead, most charts focus on ICP application and percentage use, while the graphs mainly centre on theoretical modeling with respect to retention factors. As mentioned previously, the figures are monochrome or employ limited grayscale. More schematic diagrams perhaps with a limited range of colors would have greatly enhanced the overall look of the book and such features are certainly common within monographs in the same price range. This first edition is also somewhat let down by errors throughout the figures, such as missing units and confusing legends. The addition of a list of abbreviations may also be considered for subsequent editions.
Overall, the book is a valuable resource for those learning about the intricacies of this specific separation mode of analytical chemistry, with detail on theoretical background, retention modeling and adjustable parameters, and therefore being most suitable for the more advanced and specialized researcher.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.