RS (Sigma Aldrich 40133-U) to a 100 mL ˚ ask, dilute to volume with water, and mix. Prepare standard solutions for Class 1, Class 2 mix A, and Class 2 mix B residual solvents directly into the headspace (HS) vial as described by the method: • Class 1: Transfer 1 mL of Class 1 standard stock solution to a 20 mL HS vial; add 5 mL of water, cap