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In colloration with Chemical Solutions in the USA, Electro-Kinetic Technologies have introduced a unique anionic capillary coating based on a stable polymer incorporating sulphonic acid functional groups (abbreviated as NaAMPS) and a corresponding positive charged capillary which is particulary suited to the separation of basic proteins. The NaAMPS for is available in a range of capillaries with different, but pH independent EOF rates. Zero flow capillaries are also available. NaAMPS capillaries are manufactured under the strictest GMP/GLP conditions in order to ensure reliability and excellent batch to batch reproducability. In contrast to most other coating materials, NaAMPS coated capillaries are extremely stable and have a considerably long lifetime. This polymeric coating with surface sulphonic acid groups (NaAMPS coating) has, unlike bare silica, a clearly defined pKa value. The surface is therefore fully ionised over a wide pH range. The leads to 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 analtye 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 from EKT with 3 different surface charge densities which enable the user to choose which degree of electro-osmotic flow is 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 focussing avoiding the need for complex and costly additives Advantages of NaAMPS Decreased Sample - Wall Interactions pH Independent Electro-Osmotic Flow Adjustable Electro-Osmotic Flow Reproducable Manufacturing Process Good Stability and Lifetime Acidic Compounds on Bare Silica Analytes 1. Methyl Phenol (marker), 2. 2-naphthalenesulphonic Acid, 3. Benzenesulphonic Acid At pH 8.7 the EOF carries the analytes towards the detector despite their own motion in the opposing direction. At pH 4.0 the EOF is no longer strong enough and the acidic sample now migrate in the opposite direction. Acidic Compounds on NaAMPS Coated Silica The use of NaAMPS coated capillaries shows that the separation is very stable to changes in pH which ensures greater method ruggedness. Anodic Flow Coated Capillaries (Positively Charged pH Independent) Complementary to our NaAMPS capillary is the anodic flow capillary which has permanent positive charges incorporated into the polymer matrix. This leads to a reversal of the normal direction of the electro-osmotic flow, i.e., towards the anode (anodic flow). The positive charge on the capillary wall means that basic proteins which are normally problematic can be easily separated at low pH without problems of wall adsorption. Compare the diagram which shows the attempted separation of basic proteins on bare silica. Interaction with the wall leads to poor peak shape and low efficiency. With the anodic flow capillary sharp peaks are obtained for all compounds.

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