Abstract

Detection of iron oxide in pharmaceutical formulations using electrospray ionization mass spectrometry (ESI-MS) following iron complexation with 1,10-phenanthroline (Phen), 1-(2-pyridylazo)-2-naphthol (PAN), and 4-(2-pyridylazo)resorcinol (PAR) was evaluated. Complexation of Fe III with PAR was found to produce a distinctive and sensitive mass spectral signal when compared to the other ligands. In selected ion monitoring (SIM) scan mode, the signal at m/z 484 arising from the iron-PAR complex gave a limit of detection of 2 oM for total iron using a triple-quadrupole mass spectrometer. The range of the calibration curve was determined to be 2 - 43 oM total iron. Trace iron interferences from the labware and instrumentation were minimized considerably by selection of an optimized cleaning protocol and instrument replumbing using PEEK ® tubing. Figures of merit for total iron analysis (specificity, linearity, precision and accuracy, robustness, and stability) were within the acceptance criteria of the US FDA validation guidelines for the pharmaceutical industry. Recovery of 93% of the added iron indicated a satisfactory extraction procedure for tablets containing iron oxide pigment. There was no statistical difference between the results obtained by ESI-MS and a conventional method such as inductively coupled plasma-optical emission spectroscopy (ICP-OES). The proposed ESI-MS method was found to be specific, sensitive, and relatively inexpensive since it can be performed on a mass spectrometer equipped with an ESI source, which is standard instrumentation in the pharmaceutical industry. Thus, the method validated here provides an alternative to laboratories that do not have specialized and dedicated instrumentation for elemental analysis.