## 1 Introduction  
Chromatography, and ion exchange chromatography in particular, is a widely used separation and purification technique at the biotechnological industrial scale. However, the process consumes a large amount of salt for elution and requires specifically functionalized resins. An alternative which circumvents these disadvantages is potential-controlled chromatography (PCC) or electrochemically modulated liquid chromatography (EMLC), both of which have been known to scientists for several decades [1; 2; 3; 4; 5; 6; 7; 8]. Here, the surface charge of a conductive resin is modified by an applied electrical potential. Consequently, a selective interaction between charged or polarized molecules and the charged particulate packed bed surface takes place because of electrosorption. In a subsequent step, the adsorbed molecules are forced to desorb by a change in the potential direction without any further additives. With this advantage, PCC is a promising and flexible technique, which is inexpensive and seems suitable for all types of charged or polarized molecules. Initially addressed in the second half of the 20 th century by researchers like [PERSON] [8] and [PERSON] et al. [2], the process concept of EMLC was developed as an analytical methodology, used to separate metal ions through the influence of electric potential gradients. Other researchers followed the concept and investigated the separation of inorganic [9; 10; 11] and organic compounds [12; 13; 14]. The [PERSON] group [15; 16; 17; 18; 19; 20; 21], however, carried out a major part of the process's development, studying the retention time of different molecules combined with several resin materials [22; 23] and mobile phases [24; 25], [PERSON] et al. [26] and [PERSON] et al. [27] pushed the development of PCC further by extending the process from the analytical to the preparative scale. They employed a packed bed electrode of spherical, non-functionalized glassy carbon particles which had a relatively small specific surface area (\(<\)10 m\({}^{2}\)/g) [26; 27]. Recently, [PERSON] et al. [28] implemented multi-walled carbon nanotubes (MWCNTs; Baytubes C150P) as an innovative packed bed electrode material with high specific surface area (\(\approx\)200 m\({}^{2}\)/g). Indeed, MWCNTs have already been introduced as a resin for typical gas or liquid chromatography applications [29; 30; 31; 32; 33], and as electrodes material in batteries and in sensor science [34; 35; 36; 37]. Nevertheless, the nanotubes agglomerate in complex morphology, which depends on the setup geometry, the mobile phase and numerous external parameters. Hence, the interactions of this carbon material with liquid media are still hotly debated in the literature and are not yet fully understood. Furthermore, predicting the adsorption behavior on MWCNTs under potential is challenging, and the effects inside the MWCNT electrode matrix are largely unknown. Even if the innovative material is already broadly applied [38; 39; 40; 41; 42] and has decisive advantages compared to other conductive stationary phases, its use for PCC is still in its infancy. Descriptions of the behavior of the particulate MWCNT matrix under the influence of an electrical potential are required and multiscale concepts for analyzing the relation between electrical current, mobile phase and column capacity are essential for developing a process convertible to the technical scale [43; 44]. To fill this gap, we present here a characterization of the particulate MWCNT electrode in an aqueous system. We describe the interaction of the electrode with charged molecules and the process performance under electrical potential. Based on the work of [PERSON] et al. [28], and due to the fact that Baytubes C150P (Bayer Materials Science AG, Germany) are no longer commercially available, we establish a new type of non-functionalized, low-cost and easily accessible MWCNT (CNT-K, Future Carbon GmbH, Germany) as a resin and closely examine several processing features.