Ionic Coated CE Capillaries

NaAMPS Coated Capillaries (Negatively Charged pH Independent)

In collaboration with Chemical Solutions in the USA, Electro-Kinetic Technologies have introduced a unique anionic capillary coating based on a stable polymer incorporating sulfonic acid functional groups (abbreviated as NaAMPS) and a corresponding positively charged capillary that is particularly suited for the separation of basic proteins. NaAMPS capillaries are available in a range of types with different, but pH-independent EOF rates, including zero flow capillaries.

NaAMPS capillaries are manufactured under the strictest GMP/GLP conditions to ensure reliability and excellent batch-to-batch reproducibility. Unlike most other coating materials, NaAMPS coated capillaries are extremely stable and have a considerably long lifetime. This polymeric coating with surface sulfonic acid groups (NaAMPS coating) has a clearly defined pKa value, fully ionizing the surface over a wide pH range. This results in a reasonably constant EOF over the same pH range. The figure below shows the comparative EOF rates on bare silica and an EKT capillary with NaAMPS coating.

Effect of pH on EOF for Bare Silica Compared to NaAMPS Coated Silica

When developing methods for bare silica CE by varying the buffer pH, it can become confusing as changes in pH alter both the analyte electrophoretic mobility and the EOF. The use of NaAMPS coated capillaries allows the user to easily assess the effect the change of pH has on the selectivity for their samples without the inconvenience of EOF changes. NaAMPS capillaries are available with three different surface charge densities, allowing the user to choose the degree of electro-osmotic flow required.

NaAMPS Capillary Types

High Flow - Where a high electro-osmotic flow is required over a large pH range.
Medium Flow - Medium density surface charge, produces a moderate electro-osmotic flow.
Low Flow - Generates a low EOF and is particularly useful for isoelectric focusing, avoiding the need for complex and costly additives.

Advantages of NaAMPS

Decreased Sample-Wall Interactions
pH Independent Electro-Osmotic Flow
Adjustable Electro-Osmotic Flow
Reproducible Manufacturing Process
Good Stability and Lifetime

Acidic Compounds on Bare Silica

Analytes

Methyl Phenol (marker)
2-naphthalenesulphonic Acid
Benzenesulphonic Acid

Acidic Compounds on NaAMPS Coated Silica

The use of NaAMPS coated capillaries shows that the separation is very stable to changes in pH, ensuring greater method ruggedness.

The use of NaAMPS coated capillaries has several implications for CE and MECC method development:

Improves separation efficiency for biomolecules
Allows the use of a wide pH range to adjust selectivity without affecting EOF
Ideal for chiral separations
Enables MECC operation over a wide pH range

Anodic Flow Coated Capillaries (Positively Charged pH Independent)

From the earliest days of CE, it was realized that poor peak shapes, often observed with bases and biomolecules, were mainly the result of interactions between the analyte and the capillary walls. Often, protein separations were carried out at high pH well above their isoelectric points to ensure that both the wall and the analyte were negatively charged. Although effective for some separations, this approach effectively removes the choice of pH as a separation variable.

To overcome this limitation, Capital Analytical's anodic flow capillaries have a permanent positive charge built into the polymer coating, resulting in a reversal of the normal direction of the electro-osmotic flow (EOF) towards the anode (anodic flow). This permits the separation of bases and basic proteins over a wider pH range. Interaction with the wall leads to poor peak shape and low efficiency. With anodic flow capillaries, sharp peaks are obtained for all compounds, and the presence of fixed positive charges reverses the EOF direction compared to bare silica.

The separation of basic proteins using anodic flow capillaries at acidic pH values results in vastly improved peak shape, and the elution order of components is reversed.

Ordering Information

Anodic Flow Coated Capillaries The open-format capillaries are supplied precut to the required size with the UV window correctly positioned to fit the specific instrument manufacturer's cartridge system. The capillary ends are expertly cut to ensure precise sampling.