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A novel and simple method to detect isothiazolinone-type biocides (2-methyl-3-isothiazolinone (MI), 5-chloro-2-methyl-3-isothiazolinone (CMI), 1,2-benzisothiazolinone (BIT) and 2-octyl-3-isothiazolinone (OIT)) in paper used for food packaging by ultrasonic extraction coupled with UPLC-MS/MS was developed. Parameters affecting process efficiency such as extraction solvents, UPLC mobile phase, gradient elution procedure and MS/MS conditions were studied to optimise the operating conditions. Using the optimised gradient elution procedure, the retention time was less than 6 min. The limits of detection (LODs) were found to be between 0.001 and 0.010 mg kg⁻¹, which was validated using actual concentrations. After diluting the standard solution with a blank matrix, the linear calibration curve ranges were 0.002-1.000 mg kg⁻¹ for BIT and OIT, 0.005-1.000 mg kg⁻¹ for MI, and 0.020-1.000 mg kg⁻¹ for CMI, with correlation coefficients higher than 0.9985 (n = 6). A good level of precision with a mean recovery greater than 81.3% and a relative standard deviation (RSD) less than 6.2% were also obtained. A methodology has been proposed for the analysis of isothiazolinones in paper.