Azithromycin "ghost peak": A solution degradation product of azithromycin via leaching from borosilicate glass volumetric flasks and vials

"Ghost peaks" in reversed-phase liquid chromatography separation of an electron-rich aniline compound: Mechanism and solution for this phenomenon

Two "ghost peaks" appeared in the process of developing an impurities analytical method for an electron-rich aniline compound by RP-HPLC. Surprisingly, the "ghost peaks" disappeared when the mobile phase was re-prepared. The "ghost peak" slowly began to reappear and gradually increased after increasing the injection volume or changing different instruments and columns. In this paper, the structures of two "ghost peaks" were analyzed by LC-MS/MS, which were identified as the dimer of the main peak and the oxidation products of the dimer. The mechanism was confirmed by studying the "ghost peaks" appearance phenomenon in the mobile phase with different pH values, different types of buffer salts, and different brand chromatographic columns. The potential chemical behavior of this type of compound on the column was clearly revealed in the process of RP-HPLC separation. The coupling reaction of electron-rich aniline compounds can be induced by partial or complete dissociation of the silanol group to Si-O-in the stationary phase of a reversed-phase chromatographic column under neutral and basic conditions of the mobile phase. Adding inorganic salts to the mobile phase can inhibit the reaction, and the higher salt concentration, the stronger the effect.

Advanced Dye Sorbents from Combined Stereolithography 3D Printing and Alkali Activation of Pharmaceutical Glass Waste

Additive manufacturing (AM) technologies enable the fabrication of objects with complex geometries in much simpler ways than conventional shaping methods. With the fabrication of recyclable filters for contaminated waters, the present work aims at exploiting such features as an opportunity to reuse glass from discarded pharmaceutical containers. Masked stereolithography-printed scaffolds were first heat-treated at relatively low temperatures (680 and 730 °C for 1 h) and then functionalized by alkali activation, with the formation of zeolite and sodium carbonate phases, which worked as additional adsorbing centers. As-sintered and activated scaffolds were characterized in terms of the efficiency of filtration and removal of methylene blue, used as a reference dye. The adsorption efficiency of activated printed glass was 81%. The 3D-printed adsorbent can be easily separated from the solution for reuse.

"Ghost peaks" of olmesartan medoxomil: Two solution degradation products of olmesartan medoxomil via oxidation mediated by metal ions

Two unknown solution degradants were found during the dissolution testing in 0.1-M HCl for olmesartan medoxomil (OLM) tablets. The structure of the degradants was identified and characterized by liquid chromatography-ultraviolet (LC-UV), liquid chromatography with tandem mass spectrometry (LC-MS/MS), and nuclear magnetic resonance (NMR) and demonstrated to be cyclization of tetrazole and benzene in the olmesartan (OL) and OLM structures. A series of studies including stress studies, simulation studies, and mechanism-based studies were performed to reveal the potential mechanisms that lead to the formation of the unknown degradants. The study results demonstrated that the degradation was catalyzed with radicals that originated from the metal ions leached from the inner surface of high-performance liquid chromatography (HPLC) glass vials with dissolved oxygen under acidic condition. Prerinsing the glass vials with acidic solution dissolved with EDTA can effectively avoid the generation of such oxidative impurities. The present work provides new insights into the understanding of degradation pathways of OLM, which might support the development of OLM tablets.