# Methacrylate Polymer Monoliths for Separation Applications
## 3 Applications of Methacrylate Polymer Monoliths in Separation Science
### Separation and Pre-Concentration of Chemical Species
#### 3.1.2 Chemical Separations  
Alkyl-benzenes are one of the widely used sets of compounds for testing and evaluating the performance of various chromatographic stationary phases. Their use as test compounds has also extended to monolithic stationary phases. Being non-polar, they are ideal candidates for the evaluation of reverse phase separation performance. The longer the alkyl chain, the more non-polar the molecule, and, hence, the longer its retention time on a non-polar column or monolith. Indeed, one of the first reports on the use of methacrylate monoliths in chromatography discussed the separation of a series of benzene and polystyrene analogues [3]. [PERSON] _et al._[31] prepared a monolith modified with magnetic iron oxide nanoparticles and separated pesticides and an alkyl-benzene mixture on it. A significant increase in the retention times of the pesticides and the alkyl-benzenes was observed when the monoliths were functionalized with the nanoparticles. This was attributed to the increased surface area due to the presence of the nanoparticles, and therefore an increase in the interactions between the analytes and the stationary phase. This led to better separation and more resolved peaks, indicating the potential of nanoparticle functionalized monolithic stationary phases. However, the monoliths exhibited no increase in selectivity for the pesticides after modification with the nanoparticles. This was attributed to the possibility that the nanoparticles were themselves covered with a layer of the methacrylate co-polymer. The authors observed that since the nanoparticles had vinyl groups, it was likely that these reacted with not just the methacrylate polymer on the walls of the capillary but that polymer layers appear to have built up on the nanoparticles themselves. Hence, while nanoparticles afford a higher surface area, the lack of improved selectivity for certain analytes can occur due to this unwanted reaction. Rapid, reproducible separations of alkyl-benzene mixtures were demonstrated by [PERSON] _et al._[128] using a butyl methacrylate-ethylene di-methacrylate monolith. The same monolith was also used to separate pesticide mixtures. Critically, the monoliths reported in this contribution were produced on a large scale and showed good isocratic separation even for the test solution of small molecules. Polycyclic aromatic hydrocarbons have also been separated via reverse phase and capillary electro-chromatography on methacrylate monoliths. [PERSON] and co-workers [68] carried out the polymerization of glycidyl methacrylate and EDMA inside cyclic olefin co-polymer microchannels and used this monolithic stationary phase to separate PAH mixtures via Capillary Electro-Chromatography (CEC). Increased concentration of photo-initiator led to improved separation however the devices suffered from weak anchoring of the monoliths to the Cyclic Olefin Co-polymer COC walls, leading to voids and gaps between the stationary phase and the walls which in turn lead to band broadening. In addition, it was noted that low pressures were required to avoid removal of the monolith. However, it did demonstrate the feasibility of using a single photo-initiator for both the anchoring of the monolith to the capillary walls and the polymerization step. [PERSON] _et al._[35] prepared a methacrylate ester monolith with a tight pore size distribution and used a PAH mixture to evaluate the performance. Baseline separation of the mixture was achieved via CEC separation, however the authors reported similar efficiencies when the monolith was used in the HPLC mode. Better flow characteristics were obtained using CEC. Interestingly, even though the surface areas of the high-density monoliths in CEC were low, similar retention factors were observed for the separation as on a packed silica column. Figure 10 shows a separation of a PAH mixture on a low-density monolith operating in the CEC mode.