Research On The Theory And Applications Of Chemometric Methods For Quantitative Liquid Chromatography-mass Spectrometry

Tandem mass spectrometry coupled to liquid chromatography (LC-MS/MS) is apowerful technique and has been used in many applications due to its high sensitivityand selectivity. However, the problem of signal instability associated with massspectrometry limits the quantitative application of LC-MS/MS. Factors contributing tosignal instability include the gradual fouling of the ion source, vacuum instability, andaging of the ion multiplier and the headspace sampler, which could lead to changes insensitivity and gradual drifting of baseline signal intensity over time. Variations insensitivity and baseline signal intensity could significantly deteriorate the predictioncapability of calibration models established for LC-MS/MS. Therefore, how tomaintain the long term stability of a calibration model is of utmost important for therouting quantitative application of LC-MS/MS. In this thesis, a multiplicative effectsmodel with a parameter accounting for the variations in overall sensitivity over timewas proposed to reduce the effects of signal instability on quantitative results ofLC-MS/MS and hence realize accurate quantitative analysis using calibration modelsestablished on LS-MS/MS data constructed from large standard samples withouthaving to repeat their measurement even when variations occur in sensitivity andbaseline signal intensity. The main contents of this thesis are as follows:In Chapter2, the interface technologies of LC-MS/MS and the principle of ESIsource was discussed in detail. Ionization efficiency of ESI source was investigatedthrough the analysis of the hydrolysates of a specific peptide sequence(TTVSKTETSTVASKTEGALSK). Experimental results showed that ionizationefficiency of ESI sources is roughly consistent for peptide hydrolysates.In Chapter3, the impacts of signal instability associated with mass spectrometryon quantitative results of LC-MS/MS assays were explicitly studied. A novelmultiplicative effects model for mass spectrometry (MEMMS) was proposed to solvethe problem of signal instability in quantitative liquid chromatography-massspectrometry. The performance of the proposed method was tested on aproof-of-concept model system, i.e., determination of the target peptide in two sets ofmixtures of peptide digests (the experimental time interval between the two sets ofsamples is15days).In Chapter4, the MEMMSmodel was applied to the quantification of melamine and metronidazole in two sets of milk powder samples. Experimental results revealedthat MEMMScould provide quite satisfactory concentration predictions for bothmelamine and metronidazole in milk powder samples.