Ultra-fast determination of caffeine, dipyrone, and acetylsalicylic acid by capillary electrophoresis with capacitively coupled contactless conductivity detection and identification of degradation products

• The proposed system (CE-C4D) allows fast and simultaneous determination of dipyrone, caffeine, acetylsalicylic acid, and its degradation products.
• It is the first time that methylamine was identified (CE–ESI–MS) as a hydrolysis product derived from dipyrone (metamizole).
• Fast stoichiometry determination of dipyrone sodium salt in raw material and in pharmaceutical samples without sodium as excipient.
• All information has been obtained with a single electropherogram (in less than 1 min).

Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) was used for fast, simultaneous determination of dipyrone (DIP), caffeine (CAF), and acetylsalicylic acid (ASA). In the same run and in less than 1 min, the degradation products from DIP and ASA were also detected. In addition, the usage of the CE-C4D system allowed, for the first time, the detection of methylamine as a degradation product of DIP. Capillary electrophoresis with electrospray mass spectrometry experiments were carried out in order to confirm the formation of methylamine. The limits of detection by CE-C4D were 5, 5, and 6 μmol L−1 for CAF, DIP, and ASA, respectively. The proposed method was applied to the analysis of these compounds in pharmaceutical formulations with similar results to those achieved by HPLC (p < 0.05).