Quantitative analysis of small pharmaceutical drugs using a high repetition rate laser matrix‐assisted laser/desorption ionization source

Abstract

In this work, a high repetition rate laser matrix-assisted laser desorption/ionization (MALDI) source is studied on a quadrupole-time-of-flight (QqTOF) and a triple quadrupole (QqQ) mass spectrometer for rapid quantification of small pharmaceutical drugs. The high repetition rate laser allows an up to 100-fold higher pulse frequency as compared with regular MALDI lasers, resulting in much larger sample throughput and number of accumulated spectra. This increases the reproducibility of signal intensities considerably, with average values being around 5% relative standard deviation after taking into account the area ratio of the analyte to an internal standard. Experiments were conducted in MS/MS mode to circumvent the large chemical background due to MALDI matrix ions in the low mass range. The dynamic range of calibration curves on the QqTOF mass spectrometer extended over at least two orders of magnitude, whereas on the QqQ it extended over at least three orders of magnitude. Detection limits ranged from 60-400 pg/microL on the QqTOF and from 6-70 pg/microL on the QqQ for a series of benzodiazepines. The benzodiazepine content of commercial pill formulations was quantified, and less than 5% error was obtained between the present method and the manufacturer's certified values. Furthermore, a high sample throughput was achieved with this method, so that a single MALDI spot could be quantitatively scanned in as little as 15 s, and an entire 96-well MALDI plate in 24 min.

Biomedical application of MALDI mass spectrometry for small‐molecule analysis

“…A triple quadrupole instrument, however, reaches a higher duty cycle of almost 100%, which results in highly sensitive measurements. Direct comparison of MALDI-QqTOF and MALDI-triple quadrupole showed indeed that MALDI-triple quadrupole offers $10-fold better detection limits than MALDI-QqTOF (Hatsis et al, 2003). Furthermore, the dynamic ranges of the calibration curves obtained with MALDI-triple quadrupole were $1 order of magnitude larger than those obtained with MALDI-QqTOF.…”

“…In MALDI-MS, however, the sample analysis time is primarily determined by the number of laser shots needed to generate an average mass spectrum of high quality and the repetition rate of the laser used. Dwell time of the ions does not contribute significantly to the analysis time, although the detection time of ions can take second(s) per scan in Fourier-transform ion cyclotron resonance (FTICR) MS and Orbitrap MS. With a high repetition rate laser that fires at 1,000-2,000 Hz, an averaged mass spectrum of high quality can be obtained in a few seconds with MALDI-time-of-flight (TOF) MS or MALDI-triple quadrupole MS (Hatsis et al, 2003;McLean, Russell, & Russell, 2003;Moskovets et al, 2006;Rathore et al, 2008). For quantitative analysis of, for instance, HIV protease inhibitors, analysis times for a single spot on the target plate have been reported of $3 min for MALDI-FTICR MS (20 Hz laser), $30 sec for MALDI-TOF MS (50 Hz laser), and $5 sec for MALDI-triple quadrupole MS (1,000 Hz laser; van Kampen et al, 2006Kampen et al, , 2008aKampen et al, ,b, 2009b.…”

“…MS/MS is widely used for bioanalysis with LC-MS/MS, and triple quadrupoles are regarded as the cornerstone mass analyzer for targeted quantitative analysis of small molecules. Recently, a MALDItriple quadrupole mass spectrometer was developed (Hatsis et al, 2003;Corr et al, 2006). In the selected reaction-monitoring (SRM) mode of a triple quadrupole instrument, isobaric matrix ion interferences can be removed by monitoring only compoundspecific precursor/product ion transitions.…”

“…In this respect, firing the laser at a higher frequency is advantageous to obtain a good precision without compromising sample analysis times. Comparison between laser firing at 20 and 1,000 Hz for analysis of clonazepam and nordiazepam showed that the higher laser frequency improved the within spot and spot-to-spot precisions by at least a factor of 5 (Hatsis et al, 2003).…”

Interpretation of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra of transition metal complexes in the presence of matrix adducts

“…However, accuracy of intensities is not a strong point of MALDI-TOF data in usual practice. 8 To test the reliability of the isotope patterns observed in this work, we ran ten spectra of the same Ru(bpy) 3 (PF 6 ) 2 /ATT sample (each spectrum an average of 50 shots). We examined the intensities of the peaks in the undistorted m/z 570 cluster, [Ru(bpy) 3 ] þ , normalized to 100 for the largest peak, and calculated the average deviation for each peak in the cluster relative to the intensity of that peak.…”