ACE 100Ã… HPLC Columns - Optimising Selectivity

ACE fully validated columns are available in

• C18,
• C18 AR
• C8,
• C4,
• CN,
• Phenyl,
• AQ,
• SIL
• C18-HL  chemistries

in

• 3 µm
• 5 µm
• 10 µm
• 15 µm  particle sizes.

Each ACE phase offers significantly different  hydrophobic or polar selectivity.

Figure below demonstrates the alternative selectivities shown for a series of closely related tricyclic antidepressants. The C4, C8 _{and C18 phases show the expected increase in hydrophobic} character without a major change in solute selectivity. However, significant changes in polar selectivity are clearly demonstrated with both cyano and phenyl phases. ^.

Traditionally, C18 or C8 bonded chemistries have been preferentially used in the majority of applications, in part reflecting the lower stability of cyano or phenyl bonded phases. However, for a number of reversed-phase ^{separations of polar compounds these latter materials provide the best selectivity. Within the ACE range of phases, al l}materials show comparable excellent stability and robustness ^{Hence for any application, the column showing optimum selectivity can be chosen without the previous limitations of bonded phase stability}

Method Development

As a general rule, retention increases with chain length of the bonded phase.

RETENTION (R):
more retentive

less retentive

It is recommended to start most method development projects with C18 or C8, knowing that if more retention and hence more resolution is needed, the next choice is C18-HL (Hi-Load). Starting with C8 offers the benefit of shorter analysis times and/or lower organic solvent use. The elution order for most compounds will be the same on the aliphatic (C18, C8, C4) phases. If a different elution order is required for compound verification or to resolve matrix components, changing to a phenyl or CN phase is simpler than trying to change selectivity by eluent changes. In many cases, the ACE CN and ACE Phenyl phases will offer a significant difference in selectivity from the aliphatic phases.

ACE AQ  is particularly recommended for applications requiring high aqueous content eluents. Improved resistance to phase collapse is seen compared to standard C18 phases.

Increase Resolution with 3µm Columns

With today's increased pace of drug discovery, fast and efficient methods are required. Short, narrow-bore columns are replacing the conventional 250 x 4.6mm versions. ACE HPLC columns are available in both 3 and 5µm particle sizes. Although 5µm particles are sufficient for most applications, greater efficiency can be obtained by using smaller particles. This increased efficiency enables the use of shorter (<150mm) column lengths, resulting in decreased analysis times. Due to the excellent flow characteristics of ACE silica, the high back pressures often encountered with other columns are eliminated.

Consider also ACE LC-MS and rapid analysis columns .

Scale up or Scale down

ACE bonded phases are available in 3, 5, 10 and 15µm particle sizes, so regardless of the application, the method can be scaled up or scaled down and the same selectivity be assured. For fast, high resolution preparative chromatography, a range of pre-packed ACE preparative and combinatorial chemistry columns are available.

Application Summary