Liquid chromatography coupled with electrospray-ionization mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry method development and applications for the analysis of food and medicinal herbs

Malachite green (MG) is a cationic triphenylmethane dye misused in fish farming industry and stores as its major metabolite, leucomalachite green (LMG) in fish tissues. Aristolochic acid (AA) referring to the major components AA-I and AA-II is a mixture of structurally related nitrophenanthrene carboxylic acids derived from herbal species Aristolochia and Asarum. Glucosinolates are ss-D-thioglucoside-N-hydroxysulfates with different aglycone moieties found abundantly in herbal species Cruciferae. This thesis focuses on the application of liquid chromatography coupled with electrospray-ionization tandem mass spectrometry (LC-ESI-ITMS/MS) methods for the analyses of food and medicinal herbs, respectively, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) methods for the direct herbal tissue analysis.;The members of the triphenylmethane dyes have shown to cause the human or animal cancers. The determination of MG and LMG in fish tissues is important for monitoring the illegal use of MG in aquaculture industry. We described in the present thesis, a LC-ESI-ITMS/MS method with "time segments" for the determination of MG and LMG in edible goldfish muscle. The homogenized fish muscle tissues were extracted and cleaned up by solid-phase extraction (SPE). The determination of MG and LMG was achieved by LC-MS/MS in multiple-reaction monitoring (MRM) mode. The developed method for MG and LMG in fish tissues met the minimum required performance limits of 2 ng/g for the sum of MG and LMG which is currently regulated by the European Commission.;For the high carcinogenicity and nephrotoxicity of AA, identification of AA-containing herbs is important. A new, sensitive and specific LC-ESI-ITMS/MS method with "time segments" has been established for the determination of AA-I and AA-II in eight Chinese medicinal herbs. The determination of AA-I and AA-II was achieved by LC-MS/MS in MRM mode. The quantitation was achieved with the internal standard method. This method was applied in the differentiation protocol and quality control for the easily confused herbs.;Different aglycone moieties in glucosinolates vary the biological activities and physical properties. A rapid screening method using LC-ESI-ITMS/MS was developed for screening different structural classes of intact glucosinolates in six Chinese medicinal herbs. The screening of intact glucosinolates was based on the detection of constant neutral loss and confirmed by the presence of group-specific product ions in their corresponding MS/MS spectra. Differentiation of intact glucosinolates was achieved through the detection of retention times and molecular masses as well as the characteristic product ions. The limits of detection were low nano-gram levels for constant neutral loss per injection. Significant variation in compositions of glucosinolates was identified in the cruciferous herbs. This method was also applied in the differentiation protocol and quality control for the easily confused herbs.;Direct tissue analysis using MALDI technique takes advantages over the conventional sample preparations for the LC-MS analysis. A MALDI-TOFMS method has been developed for the direct tissue analysis of AA-I and AA-II in seven Chinese medicinal herbs. The salts associated with the herbal sections interfering with MALDI analysis were reduced by the matrix rinsing process using MALDI matrix 2,5-dihydroxybenzoic acid (DHB) prior to matrix application. Experimental results demonstrated that the direct MALDI-TOFMS analysis coupled with matrix rinsing process allowed rapid and reliable characterization of the components in the herbal sections. The obtained results showed good agreement with analyses using the developed LC-ESI-ITMS/MS method of AA.;Direct tissue analysis of intact glucosinolates using MALDI-TOFMS method is often not sufficient for the conclusive identification. In the present study, the feasibility and capability to in situ analysis and structural characterization of the naturally occurring glucosinolates in Chinese medicinal tissues using MALDI-TOFMS with postsource decay (PSD) fragment ion mass analysis were explored. The glucosinolate profiles in the herbal sections were directly examined by the developed MALDI-TOFMS method. Mass spectrometric structural characterization of the identified glucosinolates was conducted by the optimized MALDI conditions combined with PSD fragment ion mass analysis. MALDI-PSD-TOFMS method was proved reliable for the determination of glucosinolates in two herbal sections. The obtained results showed good agreement with analyses using the developed LC-ESI-ITMS/MS method of glucosinolates.