Optimization of triple quadrupole mass spectrometer for quantitation of trace degradants of pharmaceutical compounds

LC/MS-MS is a sensitive analytical technique capable of quantifying impurities and degradation products of pharmaceutical compounds at very low concentrations. Obtaining reproducible and reliable signals near the lower limit of quantitation (LLQ) from an LC/MS-MS system requires careful tuning of the instrument as there are significantly more tuning parameters for optimization of an LC/MS-MS than for an instrument with a single mass analyzer. Using response surface methodology in conjunction with sequential design strategy, a Micromass Quattro LC triple quadrupole mass spectrometer was optimized for LLQ based on the signal-to-noise ratio (SIN) using the model pharmaceutical compound Azithromycin, (2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13-[(2,6-dideoxy-3-C-methyl-3-O-methyl-(alpha)-L-ribo-hexopyranosyl) oxy]-2-ethyl-3,4,10-trihydroxy-3,5,6,8,10,12,14-hepta-methyl-11-[[3,4,6-trideoxy-3-(dimethylamino)-(beta)-D-xylo-hexopyranosyl]oxy]-1-oxa-6-azacyclopentadecan-15-one. Statistical analyses determined that the tuning parameters impacting the signal-to-noise ratio were cone, capillary, extractor, radio frequency (RF) lens voltages and high mass resolution (HM Res 1). A mathematical model was derived that can be used to predict the signal-to-noise ratio of Azithromycin [M + H](+) over a wide tuning range and to identify a setting which maximizes the signal-to-noise ratio. Based on this model, the optimal instrument parameters were found at low extractor voltage (17 V), medium capillary voltage (3 kV), medium cone voltage (48 V), high RF voltage (0.9 V), and medium HM Res 1 (2.5). Using the optimized settings determined for Azithromycin, a standard curve for the analysis of a structurally related trace degradant (pseudo-aglycone Azithromycin) was generated from which the LLQ was determined to be 39.1 ng/mL, suggesting that the initial rate method of shelf-life prediction of pharmaceutical compounds may be tenable using LC/MS-MS. (C) 2002 Elsevier Science B.V. All rights reserved.