Sdudy On Rapid Surface Mass Spectrometry Analysis And Its Application

Desorption electrospray ionization mass spectrometry (DESI-MS) and desorptioncorona beam ionization mass spectrometry (DCBI-MS)，two rapid analysis techniques forsamples on surface, have recently been found by Cook group （Purdue University,Department of Chemistry, West Lafayette, USA.）in2004and by Ding group (ShimadzuResearch Laboratory (Shanghai) Co., Ltd, Shanghai, China) in2006, respectively. In DESI/DCBI-MS experiment, the charged spray solvent/corona beam splashed onto sample surface(on the substrate) and picked up the analyte to mass spectrometry to detect. The sample canbe directly analysed at ambient with a little pretreatment. At present, DESI and DCBI havefervidly been studied. Some research progress and achievement about ionization mechanismand efficiency including qualitative analysis, quantitative analysis and so on, were reported,but more complement research needs to be done. In this paper, the influence of substratematerial and surface geometry appearance on ionization efficiency, detection of diabetesmellitus biomarker with derivative DESI-MS, rapid identification of illegal additives in theslimming health products and the capture of organic reaction intermediates with reactionDESI-MS and DCBI-MS have been studied. The details are as follows:1. Studying the substrate effect on ionization and desorption on the basis of the relativeion source mechanism. By means of three desorption ionization mechanisms on DESIproposed by Cook group, the mode and time of spray solvent contact with sample waschanged by employing different substrate materials and surface geometry appearance of toincrease the desorptive ionization of sample molecules. Another analogous enhancement ofDESI ionization was completed by gas molecules “hold up”. The gas came from thereaction between substrate additive and doping spray solvent, and the seamless contact of gasmolecules with the analyte and the substrate additive benifited the desorption of analyte ionsunder the action of vaporization.2. Directly probing the reactive intermediates by reaction DESI-MS. Here a novelapplication of DESI-MS was demonstrated for direct probing the reactive intermediates inEschweiler–Clarke reaction. In the reductive amination reaction a primary (or secondary)amine is successively N-methylated using excessive formaldehyde and formic acid. In theexperiment, one reactant was included in the DESI spray solution and the other was put on themultilayer filter paper surface to keep the homogeneous reaction being occurred in the liquidphase. The reactive intermediates can be directly detected and unambiguously characterizedby liquid-phase reactive DESI-MS with minimal sample preparation, which could help theclues elucidation of organic reaction mechanisms. 3. Detecting diabetes mellitus(DM) biomarker by derivative DESI-MS. A biomarkeracetone in plasma sample was derived and placed on the substrate. The DESI-MS signalwas recorded. The spray solvent was methanol-water (2:1,v/v) containing acetic acid. Tandemmass spectrometry is used to confirm product ions. Qualitative and quantitative analysis ofacetone can be performed with short beforehand preparation and a few seconds analysis time.This method can achieve fast, high-throughput analysis of acetone in DM patients withspecificity and high sensitivity, which contributed to speedy diagnosis of DM.4. Rapidly identifying sibutramine as illegal additive and its derivatives in the slimminghealth products. Influencing factors on signal of DESI-MS were optimized and explorated forqualitative identification of the sibutramine, N-Monodesmethyl sibutramine andN,N-Didesmethylsibutramine. The rapid qualitative identification by MS and MS/MS andsemi-quantitative analysis of these illegal additives in food from surpermarket was realizedby our DESI-MS method.5. Monitoring intermediates in Leuckart reaction by DCBI-MS. The thermal coronabeam ion current was impacted on the reactant surface under defined temperature. Thereaction was started and the intermediates in ambient were synchronously detected byDCBI-MS. A series of intermediates of Leuckart reaction including acetone, methyl isobutylketone, ethylbutyl ketone, cyclopentanone, hyptanone and2-butanone, were determined. Itindicates that the DCBI ion source was an effective tool for MS detection of reactionintermediates. Here, inferential mechanism of Leuckart reaction was also provided as directevidence to validate the rationality.