Purity determination and uncertainty evaluation of folic acid by mass balance method

► This research established an improved Karl Fischer titration method for folic acid. ► RSD (2.9%) of the new KF method was significantly better than the old one (12%). ► New KF method could protect the sample from the moisture of air effectively. ► New KF method is suitable for thermally unstable or water-soluble substances. ► A mass balance method was built to determine the purity of folic acid.