Q3 water purification system

The active pharmaceutical ingredient (API) and three coformers were purchased from Sigma–Aldrich (St. Louis, MO, USA): S–naproxen (NPX: ≥98.5%, USP testing specifications), nicotinamide (NA: ≥99.5%), isonicotinamide (INA: 99%), and picolinamide (PA: 98%). Ethanol (anhydrous, 99.9%) was from Samchun Chemical (Seoul, Korea).
Dissolution media were a fed state simulated intestinal fluid (FeSSIF) and a pH 5.0 buffer solution. FaSSIF/FeSSIF/FaSSGF powder was obtained from Biorelevant (London, UK). Sodium chloride (NaCl, ≥99.5%), sodium hydroxide (NaOH, ≥97%), and acetic acid (CH₃COOH, ≥99%) were from Sigma–Aldrich. Deionized (DI) water with a resistivity over 18.2 MΩ·cm was supplied from a Direct–Q3 water purification system (Millipore, Burlington, MA, USA). Lastly, 1 M HCl (aq) and 1 M NaOH (aq) were obtained from Samchun Chemical (Seoul, Korea) and Daejung Chemical (Gyeonggi, Korea), respectively.

Acetonitrile and methanol used for the preparation of calibration standards, spiking solutions, sample extraction, and mobile phases for LC separation were LC-MS grade (J.T. Baker, Gliwice, Poland). Mobile phase modifiers including ammonium formate and glacial acetic acid, and formic acid were of analytical grade (Merck KGaA, Darmstadt, Germany). QuEChERS extraction kits were supplied from Agilent. Deionized water was obtained using a Milli Q (Millipore, Molsheim, France) Direct Q3 water purification system.
Individual pesticide standards were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). Triphenyl phosphate (TPP, internal standard) and isotopically labeled internal standards (ILISs) of etephon D4, and fosetyl-Al D15 were supplied from Dr. Ehrenstorfer GmbH (Augsburg, Germany). The ILIS of ¹⁸O₃-phosphonic was obtained from Toronto Research Chemicals (Toronto, ON, Canada). The purity of the ILISs was >94%.