## 3 Results and Discussion
### Effect on M-Cresol Recovery over Time  
The \(m\)-cresol recovery values were normalised over the entire time period based on values observed at initial time point. The \(m\)-cresol recovery levels from the Hum R solutions with the test materials over 31 days at 20 \({}^{\circ}\)C and 37 \({}^{\circ}\)C are presented in Figure 4a,b.  
Hum R solutions in contact with all five materials show loss of \(m\)-cresol over the 31-day test period at 20 \({}^{\circ}\)C and 37 \({}^{\circ}\)C. At 20 \({}^{\circ}\)C, solutions with Ti showed the least loss of \(m\)-cresol, with PU and R showing a loss of \(\sim\)56% and SS and PC showing a loss of \(\sim\)28% after 31 days. At 37 \({}^{\circ}\)C, solutions with Ti showed the least loss of \(m\)-cresol, with PC, PU and R showing a loss of \(\sim\)74% and SS showing a loss of \(\sim\)45% after 31 days. Comparison of the Hum R and \(m\)-cresol recovery trends reveal that recovery of \(m\)-cresol decreases with increase in loss of Hum R at 20 \({}^{\circ}\)C and 37 \({}^{\circ}\)C.  
Combining all findings from Hum R recovery, \(m\)-cresol recovery, formation of A21 and B3 desamido insulin the following conclusions can be made for the materials tested:  
PC: Hum R was found to be compatible with PC at 20 \({}^{\circ}\)C with negligible loss of insulin and very low levels of desamido insulin degradants formed though there was some loss of \(m\)-cresol observed. At 37 \({}^{\circ}\)C there appears to be insulin loss after 11 days (using method A) which was proportional to \(m\)-cresol loss observed after 11 days, here the insulin loss can be linked to the loss of protection of the insulin molecule by \(m\)-cresol and not the formation of degradants.  
SS and Ti: At 20 \({}^{\circ}\)C and 37 \({}^{\circ}\)C, the Hum R solutions were compatible over 31 days with low levels of desamido insulin degradants observed and some loss in insulin observed for SS at 37 \({}^{\circ}\)C after 21 days can be linked to loss in \(m\)-cresol observed.  
PU: Hum R loss from 11 days at 20 \({}^{\circ}\)C and 3 days at 37 \({}^{\circ}\)C. This loss in insulin was due to loss of protection by \(m\)-cresol observed and not due to formation of the desamido insulin degradants as very low levels of these were observed.  
R: Hum R loss was less than compared to other materials. The \(m\)-cresol loss is linked to higher levels of B3 (\(>\)7%) formed.  
Figure 4: (**a**) \(m\)-Cresol recovery over time for each test material at 20 \({}^{\circ}\)C and (**b**) 37 \({}^{\circ}\)C using analytical method A.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Time (days)** & **SS 20 \({}^{\circ}\)C** & **SS 37 \({}^{\circ}\)C** & **Ti 20 \({}^{\circ}\)C** & **Ti 37 \({}^{\circ}\)C** & **PU 20 \({}^{\circ}\)C** & **PU 37 \({}^{\circ}\)C** & **FC 20 \({}^{\circ}\)C** & **FC 37 \({}^{\circ}\)C** & **R 20 \({}^{\circ}\)C** & **R 37 \({}^{\circ}\)C** \\ \hline
0.08 & 2.30 & 2.37 & 2.34 & 2.33 & 2.33 & 2.34 & 2.33 & 2.35 & 1.91 & 2.39 \\
1 & 2.04 & 2.10 & 2.01 & 2.08 & 2.01 & 2.05 & 2.12 & 2.03 & 2.06 & 2.08 \\
3 & 2.08 & 2.18 & 2.19 & 2.25 & 2.07 & 2.15 & 2.16 & 2.07 & 2.14 & 2.34 \\
7 & 2.13 & 2.42 & 2.28 & 2.43 & 1.86 & 2.36 & 2.27 & 2.49 & 2.42 & 3.07 \\
11 & 1.70 & 2.15 & 1.54 & 1.50 & 1.32 & 1.06 & 1.69 & 1.94 & 2.17 & 4.26 \\
21 & 1.58 & 1.99 & 1.61 & 1.99 & 1.41 & 0.09 & 1.58 & 0.09 & 4.56 & 7.01 \\
31 & 1.39 & 2.11 & 1.55 & 2.11 & 0.75 & 0.31 & 1.53 & 5.29 & 2.67 & 7.43 \\ \hline \hline \end{tabular}
\end{table}
Table 5: B3 desamido insulin (iso-aspartate (isoAsp) and aspartate (Asp)) formed over time at 20 \({}^{\circ}\)C and 37 \({}^{\circ}\)C as a percentage of the total insulin peak area for method B.