| Ambient pressure ion mobility spectrometry(AP-IMS)is an efficient analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas.Though IMS heavily employed for military and security purposes,such as detecting drugs and explosives,the technique also has many laboratory analytical applications,recently being coupled with mass spectrometry and high-performance liquid chromatography.IMS coupled to HPLC with an electrospray ionization interface suffered from some bottle necks such as high noise level,prolonged sampling time because of signal average,and incompatible to gradient elution.When coupled to mass spectrometry,IMS also showed some drawbacks such as low sensitivity,limited resolving power.This dissertation trying to improve the performance of ion mobility hyphenated to HPLC and mass spectrometry by using multi emitter array electrospray ionization source to improve the ionization efficiency and hence improve the signal intensity,and using Hadamard Transform to improve the ducy cycle of ion mobility mass spectrometry.The developed technique and method were then applied to separate natural products,such as plant extract,anthocyanins,and herbal supplements.This dissertation also proposed a sensitive and high efficacy method for ion mobility mass spectrometry by inverting the gate pulse of IMS,which only lead to about 1%ion loss during IMMS experiments.1.Describes the first application of multi emitter electrospray array ionization source to ion mobility spectrometry aimed to improve the analytic performance of atmospheric pressure ion mobility spectrometry.Twelve emitters were aligned in a circle with 0.5 cm to improve the electrospray voltage homogeneity and decrease the shielding effect.Sildenafil and Sudan ? were used for the optimization of signal intensity and signal to noise ratio using various composition of methanol and water,and the electrospray flow were in the range of 2?30?L.min-1,the electrospray voltage were in the range of 2.5?7KV.Experimental results shows under optimized conditions,multi emitter electrospray array ionization improved the signal intensities effectively,decreased the noise level thus improved the signal to noise level up to 4.33 times.Furthermore,multi emitter electrospray array improved the tolerance both to water and to higher solvent flowrate.Multi emitter electrospray ionization efficiency improved 3.76 times on average compared to single emitter electrospray ionization under the same conditions.By interfacing HPLC and IMS with this multi ESI source,the sensitivity of HPLC-IMS analysis of PDE5 inhibitors is successfully achieved.2.The use of Hadamard transform ion mobility mass spectrometry(HT-IMMS)in the profiling of anthocyanins from different fruits is developed.Samples extracted with acidic methanol and purified with solid phase extraction,were analyzed with direct IMMS infusion.The separation of various anthocyanins was achieved within 30 seconds with resolving powers up to 110.The ion mobility drift times correlated with their mass-to-charge ratios with a correlation coefficient of 0.979 to produce a trend line for distinguishing the anthocyanins.Isomers with the same anthocyanidin but different monosaccharides were differentiated by high resolving power ion mobility spectrometry.Furthermore,mobility separated ions underwent collision induced dissociation to provide MS/MS spectra for the identification of anthocyanidin through fragmentation of the anthocyanins via loss of the saccharide group.IMMS appears to be a rapid and efficient approach for profiling and identifying anthocyanins.3.A high performance liquid chromatograph was interfaced to an atmospheric drift tube ion mobility time of flight mass spectrometry.The power of multidimensional separation was demonstrated using chili pepper extracts.The ambient pressure drift tube ion mobility provided high resolving powers up to 105 for the HPLC eluent.With implementation of Hadamard transform(HT),the duty cycle for the ion mobility drift tube was increased from 1%to 50%,thus the ion transmission efficiency was improved by over 200 times compared to pulsed mode,improving signal to noise ratio 10 times.HT ion mobility and TOF mass spectrometry provides an additional dimension of separation for complex samples without increasing the analysis time compared to conventional HPLC.4.Proposed a new method of ambient pressure ion mobility operation in which inverse ion mobility spectrometry is coupled to a time of flight mass spectrometer to improve sensitivity and decrease the gate depletion effect.In this mode of operation,the duty cycle is improved up to more than 99%from a typical value of less than 1%,improving the signal intensity by over 100 times.Another advantage of inverse ion mobility mass spectrometry is the reduction of the ion depletion effect of traditional linear ion mobility mass spectrometry,producing a sensitivity gain for low mobility molecules.Differences of sensitivity,resolving power,and ion discrimination are compared between the inverse and normal modes of operation using tetraalkylammonium standards.These results show that the sensitivity is improved significantly for various compounds and the resolving power mainly remained unchanged or slightly improved.Due to the reduction of ion discrimination as a result of the ion gate depletion effect,molecules with different mobilities possess similar sensitivity,however,the noise level in the inverse mode is highly influenced by the stability of ionization... |
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