Conventional LC-MS/MS technique has become an indispensable tool in process of identification of isomers, drug metabolites, impurities, degradation products, reaction by-products, etc. Usually, the complete structural identification of undesirable by-product is a difficult and time consuming task. Often, separation of the impurity and its further analysis by complementary techniques, such as NMR, to fully assign a structure are strongly required. One way of overcoming these difficulties is the implementation of high resolution MS and ion trap MS in order to obtain the elemental composition and fragmentation of ions, which provides significant help in the structural identification process.

In this work, we test the identification of impurities of latanoprost by spectroscopic methods (MS and NMR). Unknown impurities in latanoprost samples have been detected by normal phase and reverse phase positive ion ESI and APCI LC-UV-MS/MS with the quadrupole / linear ion trap hybried system as shown on the chromatograms below. One of these impurities was isolated from sample of latanoprost using preparative HPLC and analyzed by NMR. Structural elucidation of compounds, proposed MS fragmentation pattern and possible ways of formation of latanoprost impurities have been discussed.

A.) Normal phase – UV chromatogram

B.) Reverse phase – TIC ion chromatogram

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