A novel method for determining vitamin B1 in a wide variety of foodstuffs with or without polyphenols

► There are a few foodstuffs (green tea leaf, cocoa powder) that could not apply to official method in vitamin B1 analysis. ► Procedure of adding 10 mL of 2 mol/dm3 HCl was effective to remove the influence of these matrices. ► One of the compounds that caused the matrix influence was tannin. ► Accuracy and precision of the developed method was good enough regardless of the presence of the matrix influence.