## 2 Results and Discussion
### Application of Graphene Oxide-Modified PolyHIPE Materials in Liquid Chromatographic Separations  
The separation of alkylbenzenes on both unmodified PS-_co_-DVB and GONP-modified PS-_co_-DVB capillary columns of 229 mm length \(\times\) 200 \(\upmu\)m internal diameter (i.d.) were achieved using isocratic reversed-phase liquid chromatography (RP-HPLC) separation as shown in Figure 4. It was expected that GONP-modified polyHIPEs would have a reduced retention time due to the hydrophilic groups present on the polyHIPE surface and the observed 36% decrease in surface area for the GONP-modified column. However, when statistically analysed, it was found at 95% confidence that there was no significant change observed in retention times. Given the decrease in surface area and reduction in  
Figure 3: FTIR absorption spectra of GONP-modified polyHIPE #1 (orange) and GONP-modified polyHIPE #2 (purple) where (i) shows the OH absorption region.  
stationary phase interactions, the separation achieved by the GONP-modified column illustrated in Figure 3 shows a remarkable separation relative to the unmodified column.  
Despite the reduction in surface area, the modified material nonetheless achieved similar separation capacities (shown in Table 2), which are attributed to the changes in surface morphology and pore dimensions following addition of GONP. Previous reports, detailing hybrid GONP/silica stationary phases applied to the isocratic separation of alkylbenzenes failed to achieve a separation, where a co-elution of the target analytes was observed [38]. That the separation was maintained despite the significant reduction in surface area points to an enhanced separation mechanism for the GONP-modified material. It was hypothesised that the presence of GONPs and what we have established as a \"popcorn effect\" demonstrated in the morphology of these materials could have attributed to the superior adsorption of the analytes. This \"popcorn effect\" illustrated in the field emission scanning electron (FESEM) image of bulk-polymerised GONP-modified polyHIPE in Figure 5 below has also been observed in other GONP-modified polymers, showing that while the GONPs did not have a significant effect on the surface area of the polyHIPEs it did interestingly affect the overall morphology.  
Figure 4: Isocratic alkylbenzene separation on 22.9 cm \(\times\) 200 \(\upmu\)m internal diameter (i.d.) capillary columns of a graphene oxide nanoparticle-modified polystyrene-divinylbenzene polymeric high internal phase emulsion (GONP PS-_co_-DVB9 column (orange) and PS-_co_-DVB polyHIPE (blue). Mobile phase 50:50 acetonitrile:water, sample concentration 0.5 mg\(\cdot\)L\({}^{-1}\), injection volume 0.1 \(\upmu\)L, flow rate 5 \(\upmu\)L-min\({}^{-1}\), detection wavelength 214 nm. analytes: ethylbenzene (1), propylbenzene (2), butylbenzene (3) and pentylbenzene (4). (t\({}_{\text{void}}\) denotes time taken for void volume to reach the detector)  
Figure 5: FESEM images of (**a**) GONP-modified PS-_co_-DVB polyHIPE polymerised in bulk at magnification of 7000\(\times\) (scale bar 5 \(\upmu\)m) to show GONP-encapsulated morphology and (**b**) GONP coverage at 20,000\(\times\) (scale bar 2 \(\upmu\)m).  
In addition to the superior adsorption effects observed, the retention time repeatability of both GONP columns was excellent, (%RSD 0.3%-1.2%), as shown in Table 2. These %RSD values were comparable to a similar separation observed in the literature using capillary electrochromotography (CEC) [47; 48]. Additionally, resolution (\(R_{\text{s}}\)) between all analytes was greater than 1, meaning that all peaks could be differentiated easily. The polyHIPEs within capillary housing therefore have shown improved resolution, reduced retention times (\(t_{\text{r}}\)), and greater repeatability for the separation of alkylbenzenes, as compared to previous polyHIPE chromatographic separations.