Exsil Pure C18MS

• Phase: Proprietary C18
  • Particle size: 1.5, 3, 5, 7 and 10 µm
    • Base Silica: Exsil Pure 120A

With the following outstanding features

• High Polarity:                                Different selectivity to current phases.
• High Base Retention:                  Uses high % organic: aids MS detection
• Compatible with MS buffers:    Good with volatile buffers
• High Stability:                                No embedded phase to limit stability.
• Low MS bleed:                              Aids MS Detection
• Acids, Bases, Chelates:               All the benefits of pure silica.
• 100% Aqueous Stability:            Resists phase collapse

LC – MS:

The pharmaceutical industry is a major user of LC-MS and their interest centres on basic compounds. The MS sensitivity is increased by operating at high organic content and this has led to an interest in operation at neutral and high pH which increase the retention of bases allowing the use of high organic content mobile phases. Stable products with low bleed rates and capable of giving high efficiency separations are required. In addition, products should be capable of operating with volatile buffers and maximising the retention of bases.

Conventional reversed phase media provide low bleed and good stability but the peak shape of bases at higher pH can be a problem. Polar embedded phases give better peak shape at neutral and high pH but often suffer from bleed. They invariably give lower retention than standard reversed phase media and need lower organic content mobile phases which are opposite to the customer requirements.

Exsil Pure C18MS uniquely combines all the desirable attributes of a reversed phase media for LC-MS.

• Excellent Chromatography of Bases at pH 7

The excellent peak shape seen at low pH is maintained at pH 7 with both potassium phosphate and with the volatile ammonium formate buffers.

Column: 150 x 4.6mm         Phase: Exsil Pure C18MS, 5µm

• Low Bleed Rate

Exsil C18MS shows minimal bleed when used in LC/MS with TFA gradients. The second trace shows bleed levels typical of polar embedded/end capped product (NB factor of x10 in TIC scale).

Exsil Pure C18 MS

Typical of Polar Embedded phase.

• High Retention of Bases

Compared with conventional high purity base deactivated C18 phases, Exsil Pure C18MS shows much increased retention at neutral and high pH. The chromatograms opposite of Procaine, Quinine and Amitriptyline show that for similar retention of Amitriptyline at pH 7, a conventional phase (Symmetry C18) needs 75% MeOH while the Exsil Pure C18MS needs 90% MeOH.

This increased retention provides four important benefits

• Higher methanol level for improved MS sensitivity
• 2.5 x lower ammonium formate entering the MS   (10% aqueous vs. 25%)
• Half the backpressure due to lower viscosity.
• Faster analysis due to the potential to use higher flowrate without excessive backpressure.

In addition to the above, Exsil Pure C18MS has a number of other useful characteristics:

Conventional high purity C18 phases have similar selectivities due to the nearly identical hydrophobic/silanophillic balance. Although these phases work well, when their selectivity is inadequate, a phase with significantly different selectivity is required. Exsil Pure C18MS offers this alternative with lower hydrophobic and higher silanophillic selectivity.

Although Exsil Pure C18MS shows increased retention of bases, it still provides excellent peak shape for acids, bases and chelates.

Column: 150 x 4.6mm

Phase: Exsil Pure C18MS 5mm

Eluent:  50% MeCN/50% 50 mM KH₂PO₄, pH 3, 35^oC

1 ml/min

Aqueous Compatible

Due to its polar character, Exsil Pure C18MS resists the decrease in retention often seen in aqueous eluents between 24 and 48 hours with conventional C18 phases.