Comparison between liquid chromatography–time-of-flight mass spectrometry and selected reaction monitoring liquid chromatography–mass spectrometry for quantitative determination of idoxifene in human plasma

This study compares HPLC electrospray time-of-flight mass spectrometry and selected reaction monitoring (SRM) LC–MS for high throughput quantitative determination of a small molecule drug in biological samples. A high throughput LC–MS method was developed for quantitatative determination of idoxifene in human plasma and the evaluation was accomplished with the cross-validation of the developed LC–MS method between the time-of-flight mass spectrometer, and a triple quadrupole mass spectrometer operated in the SRM mode. A simple one-step semi-automated 96-well liquid–liquid extraction procedure was used to prepare 96 samples in approximately 30 min and a rapid gradient was used to shorten the LC run time. Time-of-flight mass spectrometry provides acquisition of full-scan mass spectra and extracted ion current chromatograms, which may be extracted from the total ion current chromatogram for peak area determination. The limit of quantitation for idoxifene in human plasma obtained with the time-of-flight mass spectrometer was 5 ng/ml based on 100-μl aliquots of human plasma, and the linear dynamic range was from 5 ng/ml to 2000 ng/ml. The quantitative LC–MS results from the time-of-flight mass spectrometer demonstrated that precision did not exceed 7.1% and accuracy did not exceed 1.7% with reference to quality control samples at three concentration levels in replicates of six. In contrast, the limit of quantitation for idoxifene in human plasma using a tandem triple quadrupole mass spectrometer was 0.5 ng/ml with a linear dynamic range to 1000 ng/ml. The results from the triple quadrupole instrument show that the precision did not exceed 2.2% and accuracy did not exceed 2.9%. The overall results suggest time-of-flight mass spectrometry may be a viable technique for high throughput bioanalytical work for the quantitative determination of a representative small molecule drug in the low ng/ml range in human plasma.