Merja Gergov

Reproducibility of product ion spectra acquired using a liquid chromatography/triple‐quadrupole mass spectrometry (LC/MS/MS) instrument over a 4‐year period, and with three other LC/MS/MS instruments, one from the same manufacturer and two from a different manufacturer, was examined. The MS/MS spectra of 30 drug substances were generated in positive electrospray ionization mode at low, medium, and high collision energies (20, 35, and 50 eV). Purity and Fit score percentages against a 400‐compound LC/MS/MS spectral library were calculated using an algorithm in which fragment intensity ratios and weighting factors were included. The long‐term reproducibility study was conducted using a brand A instrument; after 4 years the reproducibility of the product ion spectra was still 94%, expressed as average Purity score. The inter‐laboratory study involved two parts. Firstly, two LC/MS/MS spectral libraries, created independently in separate laboratories using brand A instruments, were compared with each other. The average Fit and Purity scores of spectra from one library against the other were better than 93 and 91%, respectively, when the same collision energies were used. Secondly, for the comparison of product ion spectra between brand A and brand B instruments, fragmentation conditions were first standardized for amitriptyline as the standard analyte. The average Fit scores of brand B spectra against the brand A spectral library varied between 79 and 85% at all three collision energies. These results indicate that, after standardizing the instrumental conditions, LC/MS/MS spectral libraries of drug substances are suitable for inter‐laboratory use. Copyright © 2004 John Wiley & Sons, Ltd.

The present study describes a novel approach for utilizing liquid chromatography/time‐of‐flight mass spectrometry (LC/TOFMS) in qualitative screening analysis. An LC/TOFMS method was developed for screening toxicologically relevant substances in urine samples. After solid phase extraction and LC separation, the method included full spectrum acquisition followed by automatic internal calibration, searching against a target library, and reporting positive identifications. The target library, containing 433 toxicologically relevant substances in the mass range of 105–734 Da, was created simply by entering the elemental formulas of substances into the instrument software for the calculation of their respective monoisotopic masses. In addition to parent drugs, the library contained selected urinary drug metabolites, based on their structures available in the literature. Identification was based on the exact masses of the compounds. The LC/TOFMS method provided 5–10 ppm mass accuracy for a majority of identified compounds in authentic urine samples. Compared with established thin‐layer and gas chromatographic methods, the LC/TOFMS method produced similar findings in urine with the additional advantage of metabolite identification without actual reference substances. Copyright © 2001 John Wiley & Sons, Ltd.

An automated liquid chromatographic/tandem mass spectrometric (LC/MS/MS) method is presented for the screening and confirmation of 16 β‐blocking drugs in clinical and autopsy urine samples. The described method involved C₁₈ solid phase extraction, LC separation and MS analysis on a triple‐stage quadrupole mass analyser. Samples were initially pre‐screened for the presence of any β‐blocking drugs using LC/MS with selected ion monitoring. Any compounds tentatively identified as β‐blocking drugs on the basis of their LC retention time and protonated molecular ion were then automatedly subjected to a second analysis in which the relevant MS/MS product ion mass spectra were acquired. These product ion mass spectra were then automatically searched against a 400‐substance mass spectral library containing previously acquired β‐blocking drugs. The results demonstrated that library search of β‐blocking drugs in urine with MS/MS product ion mass spectra was more reliable and produced fewer false negatives than library searching with mass spectra derived from single‐stage quadrupole MS. The limits of identification in the MS/MS product ion scan ranged from 0.02 mg l⁻¹ for carvedilol to 1.2 mg l⁻¹ for pindolol, the majority of the values being below 0.2 mg l⁻¹. Copyright © 2000 John Wiley & Sons, Ltd.