Level Febuxostat Impurity A Impurity B Impurity C Impurity D Conc.(µg/mL) Area (µV* sec) Conc.(µg/mL) Area (µV* sec) Conc.(µg/mL) Area (µV* sec) Conc.(µg/mL) Area (µV* sec) Conc.(µg/mL) Area (µV* sec) LOQ 0.4040 1237 0.4256 1310 0.4200 1281 0.4240 1197 0.4280 1365 80% 0.8080 2453 0.8512 2692 0.8400 2708 0.8480 2360 0.8560 2744 100% 1.0100 3143 1.0640 3712 1.0500 3532 1.0600 3185 1.0700 3383 120% 1.2120 3576 1.2768 4270 1.2600 4242 1.2720 3940 1.2840 4027 160% 1.6160 4749 1.7024 5524 1.6800 5296 1.6960 5073 1.7120 5437 Slope 2886 3341 3233 3115 3154 R2 0.9990 0.9960 0.9960 0.9980 1.0000 RRF 1.00 0.86 0.89 0.93 0.92

RRF-Relative Response factor, R2- Correlation Coefficient

Table 4: Linearity results.