Author
Huanwen Chen
Bio: Huanwen Chen is an academic researcher from Purdue University. The author has contributed to research in topics: Mass spectrometry & Extractive electrospray ionization. The author has an hindex of 11, co-authored 11 publications receiving 1648 citations.
Papers
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TL;DR: On-line droplet-droplet extraction occurs when a sample spray intersects a reagent electrospray; this allows continuous analysis of trace amounts of compounds directly in complex matrices including undiluted urine, milk and polluted water over extended periods of time.
437 citations
TL;DR: Desorption electrospray ionization (DESI) mass spectrometry is used to detect trace amounts of explosives present on a variety of ambient surfaces in 5-second analysis times without any sample preparation.
423 citations
TL;DR: Positive and negative ion DESI are used to characterize the active ingredients in pharmaceutical samples formulated as tablets, ointments, and liquids, and carryover effects are minimized in high-throughput on-line analysis of pharmaceutical samples.
Abstract: Desorption electrospray ionization (DESI) allows mass spectrometry to be used for on-line high-throughput monitoring of pharmaceutical samples in the ambient environment, without prior sample preparation. Positive and negative ion DESI are used to characterize the active ingredients in pharmaceutical samples formulated as tablets, ointments, and liquids. Compounds of a wide variety of chemical types are detected in these complex matrices. The effects on analytical performance of operating parameters, including the electrospray high voltage, heated capillary temperature, solvent infusion rate, and solvent composition, are evaluated and optimized. In addition to experiments in which a simple solvent is sprayed onto the solid analyte samples, reactive desorption is performed by adding reagents to the solvent spray to generate particularly stable or characteristic ions with the analytes of interest. A variable-speed moving belt was built for high-throughput sampling and used to provide rapid qualitative and s...
332 citations
TL;DR: The combined approach discussed here may prove useful in the rapid screening of biological fluids from sick patients and may help to improve the understanding of these rare diseases.
Abstract: Urine metabolic profiles of patients with inborn errors of metabolism were examined with nuclear magnetic resonance (NMR) and desorption electrospray ionization mass spectrometry (DESI-MS) methods. Spectra obtained from the study of urine samples from individual patients with argininosuccinic aciduria (ASA), classic homocystinuria (HCY), classic methylmalonic acidemia (MMA), maple syrup urine disease (MSUD), phenylketonuria (PKU) and type II tyrosinemia (TYRO) were compared with six control patient urine samples using principal component analysis (PCA). Target molecule spectra were identified from the loading plots of PCA output and compared with known metabolic profiles from the literature and metabolite databases. Results obtained from the two techniques were then correlated to obtain a common list of molecules associated with the different diseases and metabolic pathways. The combined approach discussed here may prove useful in the rapid screening of biological fluids from sick patients and may help to improve the understanding of these rare diseases.
152 citations
TL;DR: Principal component analysis (PCA) is used to shortlist compounds with potential for biomarker screening which are responsible for significant differences between control urine samples and samples from diseased animals.
Abstract: Desorption electrospray ionization mass spectrometry (DESI-MS) and nuclear magnetic resonance (NMR) spectroscopy are used to provide data on urine examined without sample preparation to allow differentiation between diseased (lung cancer) and healthy mice. Principal component analysis (PCA) is used to shortlist compounds with potential for biomarker screening which are responsible for significant differences between control urine samples and samples from diseased animals. Similar PCA score plots have been achieved by DESI-MS and NMR, using a subset of common detected metabolites. The common compounds detected by DESI and NMR have the same changes in sign of their concentrations thereby indicating the usefulness of corroborative analytical methods. The effects of different solvents and surfaces on the DESI mass spectra are also evaluated and optimized. Over 80 different metabolites were successfully identified by DESI-MS and tandem mass spectrometry experiments, with no prior sample preparation.
139 citations
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TL;DR: In DESI as discussed by the authors, electrically charged droplets are directed at the ambient object of interest; they release ions from the surface, which are then vacuumed through the air into a conventional mass spectrometer.
Abstract: A recent innovation in mass spectrometry is the ability to record mass spectra on ordinary samples, in their native environment, without sample preparation or preseparation by creating ions outside the instrument. In desorption electrospray ionization (DESI), the principal method described here, electrically charged droplets are directed at the ambient object of interest; they release ions from the surface, which are then vacuumed through the air into a conventional mass spectrometer. Extremely rapid analysis is coupled with high sensitivity and high chemical specificity. These characteristics are advantageously applied to high-throughput metabolomics, explosives detection, natural products discovery, and biological tissue imaging, among other applications. Future possible uses of DESI for in vivo clinical analysis and its adaptation to portable mass spectrometers are described.
1,307 citations
TL;DR: An overview of how the underlying philosophy of chemometrics is integrated throughout metabonomic studies is provided, including the tools applied for linear modeling, for example, Statistical Experimental Design (SED), Principal Component Analysis (PCA), Partial least-squares (PLS), Orthogonal-PLS, and dynamic extensions thereof.
Abstract: We provide an overview of how the underlying philosophy of chemometrics is integrated throughout metabonomic studies. Four steps are demonstrated: (1) definition of the aim, (2) selection of objects, (3) sample preparation and characterization, and (4) evaluation of the collected data. This includes the tools applied for linear modeling, for example, Statistical Experimental Design (SED), Principal Component Analysis (PCA), Partial least-squares (PLS), Orthogonal-PLS (OPLS), and dynamic extensions thereof. This is illustrated by examples from the literature. Keywords: Statistical Experimental Design (SED) • PCA • OPLS • Class-specific studies • Dynamic studies • Multivariate Design
1,194 citations
TL;DR: Examples of applications to small and large molecules, to in situ analysis, and to high-throughput analyses are presented and evidence is provided for both a heterogeneous charge-transfer mechanism and a droplet pick-up mechanism of ionization.
Abstract: Analytical characteristics of DESI are summarized. Examples of applications to small and large molecules, to in situ analysis, and to high-throughput analyses are presented. Evidence is provided for both a heterogeneous charge-transfer mechanism and a droplet pick-up mechanism of ionization. The speed, lack of the need for sample preparation, selectivity, and sensitivity of DESI are all demonstrated and discussed. Instrumentation is also discussed. Forensic applications as well as emerging areas of application including tissue imaging are given emphasis.
799 citations
TL;DR: A low-temperature plasma (LTP) probe has been developed for ambient desorption ionization and demonstration applications include direct analysis of cocaine from human skin, determination of active ingredients directly in drug tablets, and analysis of toxic and therapeutic compounds in complex biological samples.
Abstract: A low-temperature plasma (LTP) probe has been developed for ambient desorption ionization. An ac electric field is used to induce a dielectric barrier discharge through use of a specially designed electrode configuration. The low-temperature plasma is extracted from the probe where it interacts directly with the sample being analyzed, desorbing and ionizing surface molecules in the ambient environment. This allows experiments to be performed without damage to the sample or underlying substrate and, in the case of biological analysis on skin surfaces, without electrical shock or perceptible heating. Positive or negative ions are produced from a wide range of chemical compounds in the pure state and as mixtures in the gaseous, solution, or condensed phases, using He, Ar, N2, or ambient air as the discharge gas. Limited fragmentation occurs, although it is greater in the cases of the molecular than the atomic discharge gases. The effectiveness of the LTP probe has been demonstrated by recording characteristi...
647 citations
TL;DR: It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins, as well as to mass spectrometric analysis of complex mixtures.
Abstract: Paper spray is developed as a direct sampling ionization method for mass spectrometric analysis of complex mixtures. Ions of analyte are generated by applying a high voltage to a paper triangle wetted with a small volume (<10 μL) of solution. Samples can be preloaded onto the paper, added with the wetting solution, or transferred from surfaces using the paper as a wipe. It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins. Procedures are developed for analysis of dried biofluid spots and applied to therapeutic drug monitoring with whole blood samples and to illicit drug detection in raw urine samples. Limits of detection of 50 ng/mL (or 20 pg absolute) are achieved for atenolol in bovine blood. The combination of sample collection from surfaces and paper spray ionization also enables fast chemical screening at high sensitivity, for example 100 pg of heroin distributed on a surface and agrochemicals on fr...
620 citations