## 2 Results and Discussion
### LC-ESI-MS/MS Conditions
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Analyte 1**} & \multirow{2}{*}{**Retention Time**} & \multirow{2}{*}{**Quantitative SRM**, **Confirmation SRMs**} & \multicolumn{2}{c}{**Recovery\% at**} & \multicolumn{1}{c}{**SRM1/SRM2 Ratio**} \\  & & & **20 ng/L**, & (\(\pm\)RSD\%) \\  & & & **20 ng/L** & (\(\pm\)RSD\%) \\  & & & **\(\pm\)RSD\% (\(\pm\) 0.01)** & (\(\pm\)RSD\%) \\ \hline \multirow{3}{*}{DES} & \multirow{3}{*}{6.57} & 267\(\rightarrow\)2252, & 86.0 \(\pm\) 5.42, & \multirow{3}{*}{1.05 \(\pm\) 6.52\%} & \multirow{3}{*}{5.0} \\  & & 267\(\rightarrow\)227 & 87.4 \(\pm\) 3.10, & \multirow{3}{*}{1.081 \(\pm\) 7.29\% *} & \\  & & 267\(\rightarrow\)237 & 95.3 \(\pm\) 7.71 & & \\  & & 269\(\rightarrow\)145, & 88.0 \(\pm\) 12.8, & \multirow{3}{*}{9.03 \(\pm\) 19.9\%} & \\  & & 269\(\rightarrow\)143, & 93.6 \(\pm\) 4.10, & \multirow{3}{*}{5.27 \(\pm\) 23.1\% *} & \\  & & 269\(\rightarrow\)159, & 98.3 \(\pm\) 5.45 & 8.30 \(\pm\) 19.4\% * & \\  & & 271\(\rightarrow\)145, & 89.7 \(\pm\) 6.55, & \multirow{3}{*}{5.0} \\ E2 & 6.95 & 271\(\rightarrow\)183, & 105 \(\pm\) 6.48, & \multirow{3}{*}{5.0} \\  & & 271\(\rightarrow\)271 & 105 \(\pm\) 1.39 & & \\ E3 & 3.98 & 287\(\rightarrow\)145, & 82.4 \(\pm\) 12.4, & \multirow{3}{*}{3.0} \\  & & 187\(\rightarrow\)171 & 98.3 \(\pm\) 5.46 & & \\  & & 295\(\rightarrow\)145, & 99.8 \(\pm\) 14.4, & \multirow{3}{*}{1.45 \(\pm\) 21.3\%} & \\ EE & 6.69 & 295\(\rightarrow\)195, & 112 \(\pm\) 14.2, & \multirow{3}{*}{10} \\  & & 295\(\rightarrow\)295 & 108 \(\pm\) 2.14 & & \\ BPA & 5.62 & 227\(\rightarrow\)212, & 89.7 \(\pm\) 4.23, & \multirow{3}{*}{1.0} \\  & & 227\(\rightarrow\)133 & 100 \(\pm\) 3.84, & \multirow{3}{*}{1.56 \(\pm\) 17.3\%} & \multirow{3}{*}{1.0} \\  & & & 112 \(\pm\) 3.28 & & \\  & & & 85.6 \(\pm\) 7.98, & \multirow{3}{*}{1.0} \\
4 OP & 13.13 & 205\(\rightarrow\)106, & 109 \(\pm\) 10.3, & \multirow{3}{*}{1.00 \(\pm\) 1.02\%} & \multirow{3}{*}{1.0} \\  & & 205\(\rightarrow\)205 & 912 \(\rightarrow\) 8.18 & & \\  & & 359\(\rightarrow\)359 & 80.5 \(\pm\) 9.9, & \multirow{3}{*}{1.00 \(\pm\) 1.22\%} & \multirow{3}{*}{2.0} \\
4 NP & 13.80 & 219\(\rightarrow\)106, & 80.5 \(\pm\) 13.0, & \multirow{3}{*}{1.00 \(\pm\) 1.22\%} & \multirow{3}{*}{10} \\  & & 219\(\rightarrow\)219 & 93.3 \(\pm\) 5.88 & & \\  & & 358\(\rightarrow\)327, & 84.3 \(\pm\) 5.53, & \multirow{3}{*}{1.0} \\ PRDN & 4.34 & 327\(\rightarrow\)300, & 96.9 \(\pm\) 31.0, & \multirow{3}{*}{1.8} \(\pm\) 14.5\% * & \\  & & 327\(\rightarrow\)327, & 90.0 \(\pm\) 4.56 & & \\  & & 359\(\rightarrow\)329, & 80.2 \(\pm\) 6.56, & \multirow{3}{*}{3.82 \(\pm\) 1.97\%} & \\ PRNL & 5.02 & 359\(\rightarrow\)259, & 91.1 \(\pm\) 8.14, & \multirow{3}{*}{10.86 \(\pm\) 4.45\% *} & \\  & & 359\(\rightarrow\)359 & 88.5 \(\pm\) 15.0 & & \\ \hline \end{tabular} For analytes with more than two sensitive selective reaction monitoring transitions (SRMs) * notes ratio response SRM1/SRM3 and ** notes SRM1/SRM4 where SRM1 is the most sensitive SRM (SRM1); SRM3 is the 3 rd most sensitive SRM; and SRM4 is the 4 th most sensitive SRM. 1 See Section 3.1 for listed analytes abbreviations.  
\end{table} 
Table 1: LC-ESI-MS/MS parameters and recoveries, and limits of the quantitation method. MS sensitivity of the target analytes, particularly BPA, 4 OP, and 4 NP were significantly lower when the organic modifier was acetonitrile as compared to methanol. The use of methanol allowed for a higher percentage of organic modifiers to be used in the mobile phase, which also improved MS sensitivity. As noted previously, the extract from the SPE stage contained acetonitrile, and these extracts were diluted in a 50/50 _v/v_% mixture of methanol/acetonitrile just prior to the analysis to minimize degradation while maintaining MS sensitivity for the LC-ESI-MS/MS analysis. Several deuterated standards were evaluated for internal standard, surrogate standard, and volume check standard (extract volume determination).