GB/T 31531-2015 "Determination of Quinoline in Dyestuffs and Textile Dyeing and Finishing Auxiliaries" is applicable to the determination of free quinoline content in various dosage forms of dyes, dye products, and textile dyeing and finishing auxiliaries. The sample is dissolved in an aqueous solution and then extracted with an organic solvent. Detection is performed using a gas chromatograph equipped with a hydrogen flame ionization detector, with separation achieved via a capillary chromatographic column. Quantification is based on the peak area using the external standard method. The minimum quantification limit of this method is 10 mg/kg, with recovery rates controlled within 70% to 130%, providing an accurate detection basis for the control of harmful quinoline substances in products.