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Use of step gradients on different polymeric substrates in the separation of anions by macrocycle-based ion chromatography

1994; Elsevier BV; Volume: 671; Issue: 1-2 Linguagem: Inglês

10.1016/0021-9673(94)80225-4

1873-3778

Robert G. Smith, John D. Lamb,

Microfluidic and Capillary Electrophoresis Applications

Abstract Macrocycle-based ion-exchange columns have been used in our laboratory for the separation of anions. Column anion capacity is determined by the degree to which column macrocycles are bound with mobile phase cations. Capacity gradient separations have previously been performed by gradually changing the eluent cation from one with a high affinity for the macrocycle to one with a lower affinity over the course of the separation. In this work, we demonstrate that gradient separations can also be performed in step rather than linear fashion by switching eluent cations at the start of the separation and allowing the more strongly bound cation to slowly bleed from the column, reducing the column capacity during the separation. The column capacity is reduced at a rate determined by the rate of loss of the first cation from the column. Two different substrates were used as the basis for the macrocycle-based columns, Dionex MPIC and unsulfonated AS10 resins. The MPIC-based column showed retention characteristics similar to those that we have previously described with ramp gradients, while the AS10-based systems showed improved column efficiencies. Separations achieved with step gradients on these two substrates are comparable to linear gradients achieved with the same chemical systems, eliminating the need for pumps with gradient capabilities. Fourteen anions of widely varying character were separated on the AS10-based D222 column using a step gradient from NaOH to LiOH in just over 10 min.