Hydroorganic eluents

Typical applications of ion exchange in sugar analysis include (a) complexation of borates, which accentuates ionic interactions with the exchanger (27), (b) use of hydroorganic eluents, especially acetonitrile/water, with rigid, fine-particulate anion columns (28), (c) use of basic eluents, since most carbohydrates are weak acids with pKfl of 12-13 (29), (d) complexation with cations, Pb2+, Ca2+ and Ag+ being the most frequently employed, (e) the use of cation exchangers in a heavy metal form, e.g., Aminex HPX-85. 

Figure 27 Typical electrochromatogram of mono-, di- and triphosphate nucleotides. Capillary column, packed with 10-pm ODSS stationary phase, 20.5/27 cmx 100 pm i d. mobile phase, hydroorganic eluent containing 9.75 mM phosphate, 3.25 mM tetrabutyl-ammonium bromide and composed of 35% (v/v) acetonitrile and 65% (v/v) aqueous sodium phosphate, pH 6.50 running voltate, 20 kV, elec-trokinetic injection, 1.0 kV for 2 s. Solutes 1, CMP 2, UMP 3, AMP 4, GMP 5, CDP 6, UDP 7, ADP 8, CTP 9, GMP 10, UTP 11, ATP 12, GTP. (Reprinted from Ref. 119, with permission.)...

The interaction of the solute with the mobile phase can bring about forces opposing those of the hydrophobic effect. In addition to van der Waals forces, which are dependent upon the size of the molecule involved, electrostatic interactions play a key role in solute retention. Solutes which have polar substituents can interact more strongly with the polar hydroorganic mobile phase, leading to a decrease in retention compared to similar compounds with no polar moiety. The ionization of a solute molecule under the appropriate mobile-phase conditions, results in an increase in electrostatic attraction between solute and eluent and ultimately to a decreased c q>acity for chromatographic retention. 

---