Rapid Determination 1-deoxynojirimycin In Mulberry Leaves By DART-MS And The Study Of The Ionization Behavior Of Cyclic Polyhydroxy Compound In DART-MS

DNJ, namely 1-deoxynojirimycin, is a kind of polyhydroxy piperidine alkaloid. DNJ has many biological activities, such as lowering blood sugar, antitumor, antiviral, and so on. Mulberry leaves are the major natural plant source of DNJ. There are many reports about the detecting of DNJ in mulberry leaves. Direct analysis in real time ionization source is a kind of novel non-contact surface thermal desorption atmospheric pressure ionization source. The operation of the ion source is simple. You can analyse your sample directly, rapidly, intactly and in situ. It is the first report to use DART-MS/MS to measure the content of DNJ and identify some components in mulberry leaves. Cyclic Polyhydroxy Compound(CPHC) is a kind of component that widely present in plants and animals, such as sugars, flavonoids, alkaloids, etc. We study the ionization behavior of 20 CPHCs using DART-MS/MS in positive mode. This experiment not only provides a thought for the study of CPHC, but also can provide experimental evidence for investigating the ionization mechanism of compound when using DART as ionization source. The main study in this paper summarizes as follows:1. A new method based on Direct Analysis in Real Time(DART) ionization source coupled with triple quadrupole tandem mass spectrometry(Qq Q-MS/MS) has been developed for rapid qualitative and quantitative analysis of DNJ in mulberry leaves. Two ions produced from DNJ, [M+H]+(m/z 164)and [M-2H+H]+(m/z 162), are observed using DART-MS in positive mode. The spectra are more complicated and the mass response is much lower in negative ion mode than that in positive ion mode. Therefore, the peak areas of two ions([M+H]+(m/z 164) and [M-2H+H]+(m/z 162)) are integrated to determine the peak area of DNJ in the quantitative analysis. With the help of standard substance and the analysis of tandem mass spectrometry, Fagomine(another polyhydroxy piperidine alkaloid) and hexoses in mulberry leaves were identified. A reasonable linear regression equation is obtained in the range of 1.01-40.50 μg/m L, and the linear coefficient(R2) is 0.996. The limits of detection(LOD) and quantification(LOQ) of the method are 0.25 and 0.80 μg/m L, respectively. The range of recovery in a sample is shown to be 87.73-95.61%. The results derived from the developed DART-Qq Q-MS method agree well with those from the conventional HPLC-FLD method, which indicated that DART-QqQ-MS is an effective and reliable approach in quantifying DNJ content from mulberry leaves. The present method is of great advantage for rapid screening the mulberry leaves that contain high DNJ content.2. We used DART-MS/MS to investigate the ionization behavior of 20 different cyclic polyhydroxy compounds under the positive mode. The results indicated that cyclic polyhydroxy compounds including oxygen heterocyclic compounds were ionized to form the ammonium adduct ions [M+NH4]+. Cyclic polyhydroxy compounds containing nitrogen were ionized to generate the protonated ions [M+H]+. The spectra of compounds are different when He and N2 were used as desorbed gas. The ammonium adduct ions with 2H loss [M-2H+NH4]+ or [M-2H+H]+ were observed when using N2 to ionized the vast majority of compounds but not nearly for He. In addition, oxygen attachment ion [M+n O+NH4]+(n=1,2) or [M+n O+H]+(n=1) were seen in the spectra of some compounds while using N2 as desorbed gas. It was assumed that the formation of oxygen attachment ion was associated with the chemical structure of the compounds.3. We simulated the ionization process of the 3 types of CPHCs with different structure to deeply study the preference of forming positive ions in DART-MS. In this work, glucose, inositol and DNJ were selected as the representative molecule of the each type of CPHCs. The 3 molecules were used to react with the H+ and NH4+ ion to obtain the stable reaction product by quantum chemical calculation. The results indicated that glucose can combined with the ion NH4+ by forming hydrogen bond. The stable reaction product of glucose reacting H+ was also obtained. However, the ion [glucose+H]+ was not observed in spectra of glucose. The explanation of the phenomenon needed to further investigation of the kinetics of the reaction. Inositol reacted with NH4+ easily but hardly with H+. Inositol molecule can also combine with the ion NH4+ through hydrogen bond. The stable reaction product of DNJ reacting with the H+ and NH4+ ion were both obtained,but the ion [DNJ+ NH4]+ was observed in the spectra of DNJ. The phenomenon can be attributed to the thermodynamics and kinetics of the reaction of DNJ and NH4+. On the one hand, the results indicated that the enthalpy change of the reaction of DNJ and H+ was larger than the reaction of DNJ and H+. In addition, it was assumed that the energy barrier of the reaction of DNJ and H+ was much lower than the reaction of DNJ and H+. For the above-mentioned reasons, the reaction of DNJ and H+ was more prone to occur.