## 3 Results
### HPLC-MS/MS Method Validation
#### 3.1.5 Analytic Stability
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Fingolimod**} \\ \hline \hline \multirow{2}{*}{**Stability Conditions,**} & \multicolumn{3}{c}{**LQC–4.0 ng/mL**} & \multicolumn{3}{c}{**HQC–100 ng/mL**} \\ \cline{2-9}  & \multicolumn{1}{c}{**Mean**} & \(\pm\)**SD** & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Precision**} & \multicolumn{1}{c}{**Mean**} & \(\pm\)**SD** & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Precision**} \\  & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(CV)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(**ng/mL)**} & \multicolumn{1}{c}{**(**CV)**} & \\ \hline \hline \multirow{2}{*}{Bench-top (4 h RT) (6)} & 4.22 & 0.22 & 105.6\% & 5.3\% & 101.5 & 5.1 & 101.5\% & 5.1\% \\
1 month (storage \(-80\)\({}^{\circ}\)C) (6) & 4.06 & 0.23 & 101.5\% & 5.7\% & 88.6 & 4.7 & 88.6\% & 5.3\% \\
3 months (storage \(-80\)\({}^{\circ}\)C) (6) & 4.00 & 0.24 & 99.9\% & 6.1\% & 101.8 & 8.1 & 101.8\% & 8.0\% \\
6 months (storage \(-80\)\({}^{\circ}\)C) (6) & 3.97 & 0.17 & 99.3\% & 4.3\% & 99.4 & 7.7 & 99.4\% & 7.7\% \\
12 months (storage \(-80\)\({}^{\circ}\)C) (6) & 3.67 & 0.16 & 91.6\% & 4.4\% & 92.4 & 3.6 & 92.4\% & 3.9\% \\
1 month (storage \(-20\)\({}^{\circ}\)C) (6) & 3.59 & 0.17 & 89.7\% & 4.7\% & 86.8 & 4.3 & 86.8\% & 5.0\% \\
3 months (storage \(-20\)\({}^{\circ}\)C) (6) & 3.46 & 0.09 & 86.5\% & 6.1\% & 91.4 & 5.2 & 91.4\% & 5.7\% \\
6 months (storage \(-20\)\({}^{\circ}\)C) (6) & 3.34 & 0.17 & 83.4\% & 5.0\% & 86.8 & 2.1 & 86.8\% & 2.5\% \\ Freeze and thaw 2 nd cycle (6) & 3.45 & 0.17 & 86.2\% & 5.1\% & 85.5 & 3.8 & 85.5\% & 4.4\% \\ Autosampler (6 \({}^{\circ}\)C) 48 h & 3.46 & 0.16 & 100.2\% & 4.7\% & 84.3 & 2.4 & 98.6\% & 2.8\% \\ \hline \hline \end{tabular}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Stability Conditions,**} & \multicolumn{3}{c}{**LQC–4.0 ng/mL**} & \multicolumn{3}{c}{**HQC–100 ng/mL**} \\ \cline{2-9}  & \multicolumn{1}{c}{**Mean**} & \(\pm\)**SD** & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Precision**} & \multicolumn{1}{c}{**Mean**} & \(\pm\)**SD** & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Precision**} \\ \cline{2-9}  & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**(CV)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(ng/mL)**} & \multicolumn{1}{c}{**(**ng/mL)**} & \multicolumn{1}{c}{**Accuracy**} & \multicolumn{1}{c}{**Precision**} \\ \hline \hline \multirow{2}{*}{Bench-top (4 h RT) (6)} & 4.09 & 0.20 & 102.2\% & 5.0\% & 105.4 & 2.8 & 105.4\% & 2.6\% \\
1 month (storage \(-80\)\({}^{\circ}\)C) (6) & 4.16 & 0.42 & 104.1\% & 10.0\% & 100.3 & 5.6 & 100.3\% & 5.6\% \\
3 months (storage \(-80\)\({}^{\circ}\)C) (6) & 4.29 & 0.31 & 107.2\% & 7.1\% & 99.1 & 3.3 & 99.1\% & 3.3\% \\
6 months (storage \(-80\)\({}^{\circ}\)C) (6) & 4.05 & 0.16 & 101.2\% & 3.8\% & 109.0 & 6.0 & 109.0\% & 5.5\% \\
12 months (storage \(-80\)\({}^{\circ}\)C) (6) & 3.98 & 0.20 & 99.5\% & 4.9\% & 92.7 & 9.9 & 92.7\% & 10.7\% \\
1 month (storage \(-20\)\({}^{\circ}\)C) (6) & 3.49 & 0.19 & 87.25 & 5.6\% & 103.7 & 3.6 & 103.7\% & 3.4\% \\
3 months (storage \(-20\)\({}^{\circ}\)C) (6) & 3.56 & 0.14 & 88.9\% & 4.1\% & 98.2 & 7.9 & 98.2\% & 8.0\% \\
6 months (storage \(-20\)\({}^{\circ}\)C) (6) & 2.79 & 0.30 & _69.8\%_ & 10.8\% & 88.4 & 3.4 & 88.4\% & 3.8\% \\ Freeze and thaw 2 nd cycle (6) & 3.82 & 0.21 & 95.4\% & 5.4\% & 87.9 & 3.8 & 87.9\% & 4.3\% \\ Autosampler (6 \({}^{\circ}\)C) 48 h & 4.00 & 0.35 & 104.8\% & 8.7\% & 87.6 & 3.3 & 99.6\% & 3.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Stability of stock and working solutions of Fingolimod and Fingolimod-P.  
Six replicates of LQC (4.0 \(\upmu\)g/mL) and HQC (100 ng/mL) were analyzed under the tested conditions (Table 6).