## 2 Results and Discussion
### Investigating the Reduction of Graphene Oxide-Modified PolyHIPE Stationary Phases  
When the above column was reduced using ascorbic acid, it was expected that the retention time of the alkylbenzenes would increase. Reduction of GONPs should eliminate hydrophilic groups on the polyHIPE surface, and result in the formation of graphene. Graphene, being more hydrophobic than GONPs, was expected to improve analyte retention in the stationary phase through increased hydrophobic interactions. As shown in Figure 6, however, the peak shape and elution order of the separation remained similar to the previous separation and similar to alkylbenzene separations in the literature [49; 50; 51; 52; 53]. An increase in retention time was observed as compared to the GONP polyHIPE, which can be linked to increased hydrophobic interactions between the analytes and the reduced stationary phase, however, this increase was small as a result of the low loading of GONP in the initial emulsion. Upon increased addition of GONPs to the precursor emulsion during preparation of polyHIPEs, an unstable emulsion resulted, which is attributed to the relatively large size (250 nm) of the GO sheets [31]. Future studies will focus on the incorporation of smaller GONPs, which are anticipated to provide a more accessible functionalised surface for improved analyte-stationary phase interaction, and should result in a superior chromatographic performance [31; 32]. The larger GONPs utilised herein were likely at least embedded within the internal structure of the polymer backbone. Electrolyte concentration has also been shown to influence the stability of GONP suspensions within an emulsion, and should be further optimised to allow the optimal GONP dimension and loading to be determined [31]. An increase in intra-injection repeatability was observed, resulting in %RSD as low as 0.3% following the reduction step. These %RSD values (Table 2) were comparable to those observed in similar separations in the literature [49; 50; 51; 52; 53]. Despite the minimal variation observed in retention times and small reduction in \(R_{\text{s}}\) values, the injection repeatability was excellent with respect to the variability, \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multicolumn{1}{c}{**Column**} & \(t_{\text{r}}\) **(min)** & **RSD (\%)** & \(R_{\text{s}}\) & \(K^{\prime}\) \\ \hline
**Unmodified polyHIPE** & & & & \\ Ethylbenzene & 7.27 \(\pm\) 0.06 & 0.9 & 1.14 & \(1.15\pm 0.02\) \\ Propylbenzene & 9.62 \(\pm\) 0.10 & 0.1 & 1.26 & \(1.85\pm 0.02\) \\ Butylbenzene & 13.48 \(\pm\) 0.16 & 1.2 & 1.36 & \(2.99\pm 0.05\) \\ Pentylbenzene & 19.73 \(\pm\) 0.21 & 1.2 & 2.09 & \(4.85\pm 0.06\) \\ \hline
**GONP-modified polyHIPE** & & & & \\ Ethylbenzene & 6.94 \(\pm\) 0.02 & 0.3 & 1.25 & \(1.11\pm 0.01\) \\ Propylbenzene & 9.11 \(\pm\) 0.02 & 0.3 & 1.34 & \(1.76\pm 0.01\) \\ Butylbenzene & 12.80 \(\pm\) 0.05 & 0.5 & 1.51 & \(2.89\pm 0.02\) \\ Pentylbenzene & 18.60 \(\pm\) 0.10 & 0.6 & 1.91 & \(4.65\pm 0.03\) \\ \hline \hline \multicolumn{1}{c}{**Reduced GONP-modified polyHIPE**} & & & \\ Ethylbenzene & 7.13 \(\pm\) 0.04 & 0.5 & 0.98 & \(1.13\pm 0.03\) \\ Propylbenzene & 9.38 \(\pm\) 0.05 & 0.5 & 1.27 & \(1.78\pm 0.01\) \\ Butylbenzene & 13.26 \(\pm\) 0.09 & 0.6 & 1.42 & \(2.93\pm 0.03\) \\ Pentylbenzene & 19.41 \(\pm\) 0.06 & 0.3 & 1.66 & \(4.73\pm 0.05\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Separation performance characteristics of GONP-modified polyHIPEs and reduced GONP-modified polyHIPEs compared to unmodified polyHIPEs, \(n\) = 3. \(t_{\text{r}}\): retention time (min); RSD (%): % relative standard deviation; \(R_{\text{s}}\): Resolution; \(k^{\prime}\): Capacity factor. which is expected with monolithic columns [54]. Furthermore, the modified polyHIPE material, with a lower surface area, maintained a good separation performance, thus highlighting the potential of further developing nanoparticle-modified polyHIPES for applications in adsorption.