5
Amide-bonded silica phases are another popular choice in HILIC. The amide functionality, which is attached to the silica
surface either through a propyl or proprietary linker, cannot be charged in the pH range typical for HILIC mobile phases.
Retention is therefore less affected by ion exchange interactions. Additionally, amide phases are less prone to irreversible
adsorption (a problem often associated with aminopropyl phases) [11]. Amide columns also show good reproducibility and
stability.
Other popular HILIC phases include:
1. Diol material, which exhibit a considerable degree of hydrophilicity
2. Aminopropyl materials are used for HILIC separations, especially for carbohydrate analysis. They have, however,
shown irreversible adsorption of analytes (at least for reducing sugars), due to the reactive nature of amino
functionalities [11]
3. Cyano materials find limited applications in HILIC, as insufficient retention of most polar compounds is generally
experienced. This is due to the fact that cyano groups do not have hydrogen bond donor capabilities and
therefore are not very hydrophilic
To monitor HILIC trends, Pontén
et al
. [12] conducted a literature survey for which the results are summarized below. It
can be seen that the majority of the HILIC applications are found in the pharmaceutical and clinical markets with 46%
of the research papers being published coming from these areas. Another contributing factor to the growing success
of HILIC was its suitability for a large range of bioanalytical compounds that started to be considered at the time by the
pharmaceutical industry because of their pharmacodynamic properties [1]. A significant number of publications (18%)
relate to biotechnology applications, in particular to proteomics, metabonomics and glycomics. 25% of the applications
are distributed between a variety of areas, with food analysis being a major contributor.
HILIC application field distribution
HILIC use %
Application elds
Pharma/clinical
0
5
10
15
20
25
30
35
40
45
50
Other
Bio
Food
Inorganic
