A sensitive and specific hydrophilic interaction chromatography (HILIC) method for the separation and determination of dimethylamine (DMA) in active pharmaceutical ingredients (APIs) and in dosage forms of metformin (MET) has been developed and validated. A feasible analytical method based on HILIC coupled with mass spectrometry detection (HILIC-MS) was established using a simple sample preparation. The separation of MET was achieved on a Cortecs HILIC column using a mixture of 10 mmol/L ammonium formate adjusted to pH 4.8 and acetonitrile (25:75, v/v) at 0.8 mL/min flow rate. The a single-quadrupole mass detector was operated in positive ion mode. Quadrupole mass analyser was employed in selected ion monitoring mode using a target ion at m/z = 46 as [M+H]+. The HILIC-MS method was validated as per International Council on Harmonization (ICH) guidelines in terms of linearity, limit of detection, limit of quantification, selectivity, accuracy, precision and intermediate precision. The main benefit of the HILIC-MS method is a simple sample pretreatment and a quick and sensitive HILIC-MS analysis. The method was demonstrated to be applicable for the determination of DMA in routine quality control evaluation of commercial samples of metformin of both API and dosage forms. The HILIC-MS method was developed as a simpler and faster alternative to compendial method for determination of DMA (as specific impurity F) in MET described in European Pharmacopoeia.