Browsing by Author "Wu, Min-Li"

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Carbon fiber ionization mass spectrometry coupled with solid phase microextraction for analysis of Benzo[a]pyrene
(2019-02-21)
Wu, Min-Li
;
Chen, Te-Yu
;
Chen, Wen-Jie
;
Baig, Mirza Muhammad Fahad
;
Wu, Yi-Cheng
Solid phase micro-extraction (SPME) is an effective technique that can be used to selectively enrich trace analytes of interest from complex samples. Owing to its high sensitivity and high selectivity, mass spectrometry (MS) has been widely used as the detection tool to confirm the analytes enriched on SPME fibers. Generally, thermal desorption or solvent desorption is used to desorb analytes from SPME fibers for MS analysis. A straightforward ionization method called carbon fiber ionization (CFI), which uses a single carbon fiber (diameter: similar to 10 mu m) as ionization emitter in MS, has been demonstrated lately. Analytes adsorbed on the carbon fiber, which is placed close (similar to 5 mm) to the inlet of a mass spectrometer, can be readily ionized through corona discharge and detected by the mass spectrometer. One unique feature regarding this approach over other existing ambient ionization methods is that no additional electric contact is applied directly on the carbon fiber. Nevertheless, on the basis of the electric field provided by the mass spectrometer, corona discharge can readily occur for ionizing analytes on the carbon fiber. Carbon fiber has high affinity toward polycyclic aromatic hydrocarbons due to its graphite-like surface structure. We herein explore a hyphenated-technique by combining carbon-fiber based SPME with CFI-MS for extraction of benzo[a]pyrene (BaP), a carcinogen, from aqueous samples. After BaP are adsorbed on a carbon fiber through SPME, the SPME carbon fiber can be readily placed in front of the mass spectrometer for MS analysis. The ions at m/z 252 derived from BaP adsorbed on the carbon fiber can be immediately acquired by the mass spectrometer without the requirement of applying heating or solvent. The limit of detection of BaP using the developed method was as low as similar to 60 pM. It is also feasible to detect BaP from complex serum sample. The feasibility of using the approach for quantitative analysis of BaP was also demonstrated. The linear dynamic range toward BaP was 0.2-5 nM. The extraction efficiency using this approach for aqueous samples was similar to 91%. (C) 2018 Elsevier B.V. All rights reserved.
Carbon Fiber Ionization Mass Spectrometry for the Analysis of Analytes in Vapor, Liquid, and Solid Phases
(2017-12-19)
Wu, Min-Li
;
Chen, Te-Yu
;
Chen, Yen-Chun
;
Chen, Yu-Chie
;
應用化學系
Various ionization methods in mass spectrometry (MS) are available for the analysis of analytes with different properties. Nonetheless, the use of a single ionization method to analyze mixtures containing analytes with different polarities and volatilities in different phases at atmospheric pressure remains a challenge. Exploring an ionization method that can ionize small organics and large biomolecules with different properties for MS analysis is advantageous. Carbon fiber ionization mass spectrometry (CFI-MS), which uses a carbon fiber bundle as the ion source, is useful for the analysis of small organics with low polarities. Voltage needs to be applied on the carbon fiber bundle to initiate corona discharge for ionization of analytes. In this study, we explore the suitability of using CFI-MS in the analysis of analytes in vapor, liquid, and solid phases using a single carbon fiber (length : similar to 1 cm; diameter: similar to 10 mu m) as the ion source. Furthermore direct electric contact on the carbon fiber is not required. We demonstrate that CFI-MS is useful for analyzing not only small and low-polarity organics but also polar biomolecules, such as peptides and proteins. The limits of detection for analytes with high polarities such as dodecyl trimethylammonium bromide and bradykinin are estimated to be similar to 16 and similar to 53 pM, respectively. Ionization mechanisms, including corona discharge and electrospray, are involved in the ionization of analytes with the polarity from low to high. Furthermore, sesame oil containing aromatic volatiles and compounds with different polarities is used as a model sample to demonstrate the capability of the developed ionization method to provide comprehensive chemical information from a complex sample. In addition, the feasibility of using the developed method for quantitative analysis of nonpolar as well as medium and high polarity analytes is also demonstrated. The sensitivity of the developed method toward analytes with high polarity is higher than those with low polarity. The method precision was estimated to be similar to 7.8%.
Detection of pesticide residues on intact tomatoes by carbon fiber ionization mass spectrometry
(2019-02-01)
Wu, Min-Li
;
Wu, Yi-Cheng
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
Trace and toxic pesticide residues may still remain on crops after harvest. Thus, maximum residual levels (MRLs) of pesticides on crops have been regulated. To determine whether the remaining pesticide residue level is below MRL, time-consuming sample pretreatment is needed prior to analysis of crop samples by suitable analytical tools. By elimination of sample pretreatment steps, a high-throughput method can be developed to determine the presence of pesticide residues directly on intact crops. Carbon fiber ionization mass spectrometry (CFI-MS) is effective in determining analytes with different polarities in solid, liquid, and vapor phases in open air. Moreover, the vapor derived from solid or liquid samples possessing high vapor pressure can be readily detected by CFI-MS. The setup of CFI-MS is straightforward. A carbon fiber (diameter of similar to 10m and length of similar to 1cm) is placed close (similar to 1mm) to the inlet of the mass spectrometer applied with a high voltage (-4.5kV). No direct electrical contact applied on the carbon fiber is required. When placing the sample with certain vapor pressure underneath the carbon fiber, analyte ions derived from the sample can be readily detected by the mass spectrometer. Given that most pesticides possess a certain vapor pressure (similar to 1.33x10(-5)-similar to 1.33x10(-4)Pa), we herein develop a qualitative and quantitative analysis method to determine pesticide residues on intact fruits such as tomato based on CFI-MS without requiring any sample pretreatment. Atrazine, ametryn, carbofuran, chlorpyrifos, isoprocarb, and methomyl were selected as model samples. Low limits of detection (at nM range) were achieved for the model pesticides using the current approach. Moreover, we demonstrated that the precision and accuracy of quantitative analysis of similar to 5% and similar to 2%, respectively, could be achieved using this approach.
Selective extraction of n-butylidenephthalide from Angelica sinensis (Danggui) by using functionalized iron oxide magnetic nanoparticles as trapping probes
(2018-04-14)
Wu, Ching-Yi
;
Wu, Min-Li
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
n-Butylidenephthalide (BP) is an active compound in Angelica sinensis (Danggui) and a potential anti-cancer drug. Thus, purification of BP from complex herb extract samples is important. In this study, we develop a facile method for selective purification of BP from complex samples by using iron oxide magnetic nanoparticles (Fe3O4 MNPs) immobilized with riboflavin-50-phosphate (RFMP) as affinity probes. RFMP is a polyaromatic compound that contains a phosphate, which can readily chelate with the metal center on the surface of Fe3O4 MNPs. The aromatic rings on RFMP can interact with BP (K-d = similar to 6.73 x 10(-5) M) through pi-pi stacking. Thus, Fe3O4@RFMP MNPs are fabricated by simply mixing Fe3O4 MNPs with RFMP under microwave heating (power: 540 W) for 3 min. The as-prepared Fe3O4@RFMP MNPs can be used as affinity probes to selectively concentrate BP from an acidic solution; BP is then released from the MNPs by using acetonitrile. The recovery of BP from the Fe3O4@RFMP MNP-BP conjugates is estimated to be similar to 100%. This study also demonstrates the feasibility of using the proposed approach to selectively extract BP from complex A. sinensis extract samples.
Ultrasonication-assisted spray ionization-based micro-reactors for online monitoring of fast chemical reactions by mass spectrometry
(2019-01-01)
Chen, Te-Yu
;
Wu, Min-Li
;
Chen, Yu-Chie
;
應用化學系
;
Department of Applied Chemistry
Microfluidics can be used to handle relatively small volumes of samples and to conduct reactions in microliter-sized volumes. Electrospray ionization can couple microfluidics with mass spectrometry (MS) to monitor chemical reactions online. However, fabricating microfluidic chips is time-consuming. We herein propose the use of a micro-reactor that is sustained by two capillaries and an ultrasonicator. The inlets of the capillaries were individually immersed to two different sample vials that were subjected to the ultrasonicator. The tapered outlets of the two capillaries were placed cross with an angle of similar to 60 degrees close to the inlet of the mass spectrometer to fuse the eluents. On the basis of capillary action and ultrasonication, the samples from the two capillaries can be continuously directed to the capillary outlets and fuse simultaneously to generate gas phase ions for MS analysis through ultrasonication-assisted spray ionization (UASI). Any electric contact applied on the capillaries is not required. Nevertheless, UASI spray derived from the eluents can readily occur in front of the mass spectrometer. That is, a micro-reactor was created from the fusing of the eluent containing different reactants from these two UASI capillaries, allowing reactions to be conducted in situ. The solvent in the fused droplets was evaporated quickly, and the product ions could be immediately observed by MS because of the extreme rise in the concentration of the reactants. For proof of concept, pyrazole synthesis reaction and cortisone derivatization by Girard T reagent were selected as the model reactions. The results demonstrated the feasibility of using UASI-based micro-reactor for online MS analysis to detect reaction intermediates and products.