Quantification and confirmation of identity of analytes in various matrices with in-source collision-induced dissociation on a single quadrupole mass spectrometer

Abstract

Mass spectrometry is often used for the quantification of target analytes. When liquid chromatography (LC) is interfaced with mass spectrometry, it is generally accepted that tandem mass spectral (MS/MS) techniques are required to quantify an analyte with confirmation of identity in a complex matrix. In such applications LC is generally used to deliver the sample to the mass spectrometer with minimal separation, and the bulk of the separation is downloaded to the tandem mass spectrometer. However, LC is also a powerful separations tool, and a tandem mass spectrometer is not required to gain fragmentation data. In-source collision-induced dissociation (IS-CID) on a single stage mass spectrometer will generate rich fragmentation patterns that are often used for qualitative identification and rarely for quantitative confirmation of identity. Quantification with confirmation of identity on a single stage quadrupole mass spectrometer can be done by concurrently monitoring for the expected parent and fragment ions using multiple selected ion recording (SIR) channels. Although such methods have been used to quantify analytes with confirmation of identity in simple matrices, only isolated examples of such work with complex matrices are published. We will extend upon the previous work and discuss the utility of using single quadrupole mass spectrometers for the quantification of an analyte with concurrent confirmation of identity in complex matrices. The analysis of methomyl in spinach extract demonstrates the ability of simple LC/MS to separate out interferences and give accurate relative abundances of fragments. Sulfometuron methyl was quantified accurately out of apple matrix at a level of 200 pg/μL, even with a calibration curve run in pure solvents. β-Lactam antibiotics and lincomycin were analyzed out of bovine milk extract. The limits of detection (LOD) for the β-lactam antibiotics ranged from 15.5 to 105 pg of material on-column, and although these LODs were higher than observed with a triple quadrupole mass spectrometer, they were actually superior to those observed on an ion trap mass spectrometer. Lincomycin gave an LOD of 0.83 pg on-column, despite the fact that trifluoroacetic acid (TFA) was required to give adequate chromatography. In our final example, we demonstrate the quantification of ritonavir out of blood plasma extract. The LOD of ritonavir under these conditions was 2.2 pg on-column. For both lincomycin and ritonavir we achieve confirmation of identity even at the lowest concentrations we ran.