Chengdui Yang

Imaging mass spectrometry with a low-temperature plasma probe for the analysis of works of art.

DESI-MSI allows direct analysis of the sample withlittle or no sample pretreatment under ambient conditions.However, for analysis ofpaintings,the electrosprayedorganicsolvents may result in contamination and damage to thesample.Herein, we present a novel IMS method that uses a low-temperature plasma (LTP) probe as an ion source for theanalysis of paintings and calligraphy. For the evaluation ofartworks, the following requirements should be satisfied.First, to avoid damage and contamination of sample, nosolvent or matrix should be introduced into the ion source orsamples during the experiment. Second, analysis by the probeshould be carried out in a preparation-free approach, andtherefore an ambient ionization technique amenable to directanalysis is desirable. Finally, the spatial resolution of the IMStechnique should be sufficiently high to allow characteriza-tion of the spatial distribution of analytes. The experimentalsetup and the configuration of LTP probe are shown inFigure 1A and B, respectively (painting study provided in theSupporting Information, Figure S1). The probe is animproved version based upon the previously reported dielec-tric barrier discharge ionization (DBDI) source.

Desorption electrospray tandem MS (DESI-MSMS) analysis of methyl centralite and ethyl centralite as gunshot residues on skin and other surfaces.

Abstract:  A direct and sensitive method for the detection of methyl centralite (MC) and ethyl centralite (EC) as gunshot residues (GSRs) has been developed. This method uses desorption electrospray ionization (DESI)‐tandem mass spectrometry and directly desorbs and detects analytes from surfaces without any sampling process. Typical transitions for MC and EC, m/z 241 to m/z 134 and m/z 269 to m/z 148, respectively, were used to improve the assay sensitivity. It has been shown that MC and EC can be detected on various surfaces, with detection limits of 5–70 pg/cm2. Interferences, detection time after shooting and the number of times hands were washed after shooting were also evaluated. None of the materials interfered with the results and the detection window for organic GSRs was up to 12 h and hands could be washed at least six times. Further samples were analyzed to confirm the reliability of this method, and showed that it could discriminate shooters from nonshooters. This method should be of significance in forensic science, especially in analyzing GSRs, because of its simplicity, high throughput, and the direct detection of MC and EC on suspects’ hands, clothes, and hair.

Rapid screening of clenbuterol in urine samples by desorption electrospray ionization tandem mass spectrometry

Rapid screening of clenbuterol in urine was performed by combining desorption electrospray ionization (DESI) and tandem mass spectrometry (MS/MS). Optimization experiments were carried out including the selection of substrates, spray solutions, nebulizing gas pressures, high-voltage power supplies and flow rates of spray solution. The limit of detection (LOD), defined as the lowest quantity that can be detected, was 5.0 pg for the pure compound. Using DESI coupled with solid-phase extraction (SPE), the linear response range was from 10 to 400 ng/mL (R(2) = 0.993) and the concentration LOD for urine sample was 2.0 ng/mL. The analysis for one spiked urine sample was achieved within 4 min. In addition to the fast analysis speed, MS/MS provided structural information for the confirmation of clenbuterol. Urine samples from different people were investigated and the recoveries were within 100 +/- 20%. The developed method can potentially be used for screening of clenbuterol in doping control.

Versatile Platform Employing Desorption Electrospray Ionization Mass Spectrometry for High-Throughput Analysis

A simple and easy-to-build high-throughput analysis system was constructed. The system consisted of three major components: (1) a multichannel device with 16 parallel capillaries, (2) a desorption electrospray ionization (DESI) source, and (3) a linear ion trap mass spectrometer. When analyses were performed, the multichannel device was moved horizontally on a translation stage controlled by a step motor. Our design expands the functions of DESI, in which the liquid sample in capillary was driven out by the nebulizing gas, ionized, and then transferred to a mass spectrometer. To assess the high-throughput performance of the system, 5 mg/L 1,3-diethyl-1,3-diphenylurea (DDU) solution and 10 mg/L angiotensin I solution were alternatively loaded into the reservoirs and capillaries in the multichannel device. Results indicated that analyses of the all the samples in 16 capillaries were completed within 1.6 min, which means a throughput of 600 samples/h. Reactive DESI experiment was also successfully performed with this system to show the feasibility of online derivatization. The relative standard deviations for a single capillary and five identical capillaries were 7.6 (n = 16) and 12.3%, respectively. Linear relative abundance response was achieved for DDU (r = 0.9971).

In Vivo Nanoelectrospray for the Localization of Bioactive Molecules in Plants by Mass Spectrometry

The method for the localization of bioactive molecules in plants is highly needed since it provides a fundamental prerequisite for understanding their physiological and ecological functions. Here, we propose a simple method termed in vivo nanoelectrospray for the localization of bioactive molecules in plants without sample preparation. A capillary is partly inserted into the plant to sample liquid from a highly located region, and then, a high voltage is applied to the plant to generate an electrospray from the capillary tip for mass spectrometry analysis. Using this method, bioactive molecules such as saccharides, glycoalkaloids, flavonoids, organic acids, and glucosinolates (GLs) are detected in the target regions of living plants or fresh fruits. Original information for endogenous chemicals including liable molecules in plant can be obtained. A sketchy three-dimensional distribution of glycoalkaloids in a cherry tomato has been obtained. The present work provides a powerful tool for the study of bioactive molecules in a living plant by mass spectrometry.

Rapid Removal of Matrices from Small-Volume Samples by Step-Voltage Nanoelectrospray†

Matrix unloaded: By changing from fixed-voltage (left) to step-voltage nanoelectrospray (right), the mass-spectrometric analysis of small-volume physiological samples is possible. Separation and ionization are achieved in one process, which avoids sample loss and dilution and prevents interference by the matrix. The result is high sensitivity even for samples at the nanoliter level.

Simultaneous quantitative determination of norgestrel and progesterone in human serum by high-performance liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization.

A selective, reliable and rapid method for the simultaneous determination of progesterone and norgestrel concentrations in human serum after taking oral contraceptive tablet has been developed using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) with atmospheric pressure chemical ionization (APCI) interface. The norethisterone was used as the internal standard. Selected transitions of m/z 313/245 for norgestrel, m/z 315/97 for progesterone and m/z 299/109 for norethisterone were monitored using multiple reaction monitoring (MRM) mode for quantitation. The assay was linear over the concentration range of 0.2-50 ng mL-1 for norgestrel and progesterone. The lower level of quantitation in human serum was obtained at 0.2 ng mL-1 for both norgestrel and progesterone using optimum tuning parameters. The intra-assay precision and inter-assay precision do not exceed 10 and 9%, respectively. The method has been applied to the determination of norgestrel and progesterone in serum of female volunteers.

Development of a graphite low‐temperature plasma source with dual‐mode in‐source fragmentation for ambient mass spectrometry

A new low-temperature plasma (LTP), based on dielectric barrier discharge (DBD), has been developed as an alternative ionization source for ambient mass spectrometry. For organic samples, the source is able to produce two different fragmentation patterns which are selectable by an electrical switch. The two source modes are different only in the second electrodes: in configuration (A), bar-plate and in configuration (B), coaxial bar-cylinder shapes are used. A disposable graphite probe is used as the first electrode, the same in both configurations, and a copper foil is used as the second electrode. The ionization source is applicable to gas and liquid samples, without any change being necessary in its design. Under optimal conditions, to take ethylbenzene as an example, a detection limit of less than 25 ng was obtained and a relative standard deviation (RSD) of 13.36% has been demonstrated for 50 ng of ethylbenzene (n = 11). We have found several interesting differences in the mass spectra of the tested volatile organic compounds (VOCs) in the two modes, which might be applicable in identification studies. We have investigated the effect of variation of the first electrode material and the second electrode length in mode B. Moreover, in this design the graphite electrode is capable of acting as a sample adsorbent, which is a new sampling method for LTP mass spectrometry (MS). This capability was investigated by adsorption of the selected VOCs onto the surface of the graphite electrode in a headspace solid-phase microextraction (SPME) system, and direct desorption and ionization of the samples by LTPMS.

The Utilization of MS-MS Method in Detection of GSRs

This paper describes a novel method to detect gunshot residues (GSRs). The components contained in the double-based smokeless powder were separated by using a HPLC system with UV detection at 223 nm. The result indicated that there are mainly two kinds of organic ingredients in the double-base smokeless powder used. These two organics do not include nitrocellulose because it has no evidential value in the HPLC-UV trace of the smokeless powder sample. By matching retention times of these two compounds with that of the five standards occurring in smokeless powder, the compounds are tentatively identified as methyl centralite (MC) and nitroglycerin (NG). These two compounds were finally identified by using MS spectrum. This MS-MS method was developed to detect MC since MC is less commonly found in the environment than NG. In Chinese ammunition, MC is widely used as a stabilizer instead of EC. Sixteen samples were used to evaluate the reliability of the method. The mean (±SD) MC level in the eight samples is 520.1 ± 271.9 pg/µL and that in the blanks is 31.0 ± 20.8 pg/µL. The result (P = 0.0007) shows that there is a significant difference between the two serial data. Sampling hands over a 24 h period showed that GSR could be detected even after 8 h with a 75% decrease in the level of MC. The result of the washing test shows that it is still possible to apply the proposed method to detect GSRs on a shooters hands even if their hands have been washed three times. Another test shows that if the shooters wear gloves while firing, MC on the gloves can be easily detected using the proposed method.

Controlling Charge States of Peptides through Inductive Electrospray Ionization Mass Spectrometry

A novel ionization device for controlling the charge states of peptides based on an inductive elecrospray ionization technique was developed. This ion source keeps the major capabilities of electrospray ionization (ESI) which is compatible with liquid separation techniques (such as liquid chromatography (LC) and capillary electrophoresis (CE)) and can be potentially used to control the charge states of peptides accurately by simply varying the AC voltage applied. In comparison with conventional ESI, inductive ESI successfully simplifies the mass spectrum by reducing the charge states of peptide to a singly charged one, as well as eliminating the adduct ions.