Ambient Sampling/Ionization Mass Spectrometry: Applications and Current Trends

Current trends in explosive detection techniques

1. Scope of this Review 2270 2. Ambient Ionization Techniques 2272 2.1. Solid−Liquid Extraction-Based Techniques 2272 2.1.1. Desorption Electrospray Ionization (DESI) 2272 2.1.2. Desorption Ionization by Charge Exchange (DICE) 2277 2.1.3. Easy Ambient Sonic-Spray Ionization (EASI) 2278 2.1.4. Liquid Micro Junction Surface Sampling Probe (LMJ-SSP) 2279 2.1.5. Liquid Extraction Surface Analysis (LESA) 2279 2.1.6. Nanospray Desorption Electrospray Ionization (nanoDESI) 2280 2.1.7. Desorption Atmospheric Pressure Photoionization (DAPPI) 2280 2.2. Plasma-Based Techniques 2281 2.2.1. Direct Analysis in Real Time (DART) 2282 2.2.2. Flowing Atmospheric-Pressure Afterglow (FAPA) 2286 2.2.3. Low Temperature Plasma (LTP) & Dielectric Barrier Discharge Ionization (DBDI) 2286 2.2.4. Chemical Sputtering/Ionization Techniques 2287 2.3. Two-Step Thermal/Mechanical Desorption/ Ablation (Non-Laser) Techniques 2288 2.3.1. Neutral Desorption Extractive Electrospray Ionization (ND-EESI) 2288 2.3.2. Beta Electron-Assisted Direct Chemical Ionization (BADCI) 2288 2.3.3. Atmospheric Pressure Thermal Desorption-Secondary Ionization (AP-TD/SI) 2289 2.3.4. Probe Electrospray Ionization (PESI) 2289 2.4. Two-Step Laser-Based Desorption Ablation Techniques 2290 2.4.1. Laser-Based Hybrid Techniques Coupled to ESI or Plasma Ionization 2290 2.4.2. Laser Electrospray Mass Spectrometry (LEMS) 2292 2.4.3. Laser Ablation Atmospheric Pressure Photoionization (LAAPPI) 2293 2.4.4. Laser Ablation Sample Transfer 2293 2.5. Acoustic Desorption Techniques 2294 2.5.1. Laser-Induced Acoustic Desorption (LIAD) 2294 2.5.2. Radiofrequency Acoustic Desorption Ionization (RADIO) 2295 2.5.3. Surface Acoustic Wave-Based Techniques 2295 2.6. Multimode Techniques 2296 2.6.1. Desorption Electrospray/Metastable-Induced Ionization (DEMI) 2296 2.7. Other Techniques 2296 2.7.1. Rapid Evaporative Ionization Mass Spectrometry (REIMS) 2296 2.7.2. Laser Desorption Ionization (LDI) 2297 2.7.3. Switched Ferroelectric Plasma Ionizer (SwiFerr) 2297 2.7.4. Laserspray Ionization (LSI) 2297 3. Remote Sampling 2298 3.1. Nonproximate Ambient MS 2298 3.2. Fundamentals of Neutral/Ion Transport 2298 3.3. Transport of Neutrals 2298 3.4. Transport of Ions 2299 4. Future Directions 2300 Author Information 2300 Corresponding Author 2300 Author Contributions 2300 Notes 2300 Biographies 2300 Acknowledgments 2301 References 2301

Mass Spectrometry: Recent Advances in Direct Open Air Surface Sampling/Ionization

Ambient ionization mass spectrometry allows the rapid analysis of samples or objects in their native state in the open environment with no prior preparation. Over the past six years, the ability of these techniques to provide selective analyte desorption and ionization, in combination with mass spectrometry (MS), has provided a growing number of powerful analytical alternatives across broad application areas, both quantitative and qualitative in nature, including pharmaceutical analysis, process chemistry, biological imaging, in vivo analysis, proteomics, metabolomics, forensics, and explosives detection. With the emergence of new ambient ionization methods, and the complementary nature of existing desorption and/or ionization techniques, additional hyphenated methods have been devised, which pushes the total number of documented methods to almost thirty. To cover all current ambient ionization techniques in detail would be too complex and detract from the main objective of this review. Rather, an overview of the field of ambient ionization MS will be given, followed by broad classification to allow detailed discussion of theory and common mechanistic factors underpinning a number of key techniques. Consideration will be given to experimental design, ease of implementation and analytical performance, detailing subsequent impact on a number of application areas, both established and emerging.

Ambient ionization mass spectrometry: current understanding of mechanistic theory; analytical performance and application areas

Dalton T. Snyder,† Christopher J. Pulliam,† Zheng Ouyang,‡ and R. Graham Cooks*,† †Department of Chemistry and Center for Analytical Instrumentation Development, Purdue University, West Lafayette, Indiana 47907, United States ‡Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, United States ■ CONTENTS Ambient Ionization and Sampling 2 Vacuum Systems 4 Analyzers and Configurations 6 MEMS and Other Alternative Fabrication Methods 8 Simulations 9 Electronics and Data Systems 12 Portable Systems 19 Mesoscale Systems 20 Planetary and Space Science Systems 21 Practical Applications 22 Expectations 23 Author Information 23 Corresponding Author 23 Notes 23 Biographies 23 Acknowledgments 24 References 24

Miniature and Fieldable Mass Spectrometers: Recent Advances.

Detection of explosives is important for public safety. A recently developed low-temperature plasma (LTP) probe for desorption and ionization of samples in the ambient environment ( Anal. Chem. 2008 , 80 , 9097 ) is applied in a comprehensive evaluation of analytical performance for rapid detection of 13 explosives and explosives-related compounds. The selected chemicals [pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), cyclo-1,3,5-trimethylenetrinitramine (RDX), tetryl, cyclo-1,3,5,7-tetramethylenetetranitrate (HMX), hexamethylene triperoxide diamine (HMTD), 2,4-dinitrotoluene, 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,6-dinitrotoluene, and 4-nitrotoluene) were tested at levels in the range 1 pg-10 ng. Most showed remarkable sensitivity in the negative-ion mode, yielding limits of detection in the low picogram range, particularly when analyzed from a glass substrate heated to 120 °C. Ions typically formed from these molecules (M) by LTP include [M + NO(2)](-), [M](-), and [M - NO(2)](-). The LTP-mass spectrometry methodology displayed a linear signal response over three orders of magnitude of analyte amount for the studied explosives. In addition, the effects of synthetic matrices and different types of surfaces were evaluated. The data obtained demonstrate that LTP-MS allows detection of ultratrace amounts of explosives and confirmation of their identity. Tandem mass spectrometry (MS/MS) was used to confirm the presence of selected explosives at low levels; for example, TNT was confirmed at absolute levels as low as 0.6 pg. Linearity and intra- and interday precision were also evaluated, yielding results that demonstrate the potential usefulness and ruggedness of LTP-MS for the detection of explosives of different classes. The use of ion/molecule reactions to form adducts with particular explosives such as RDX and HMX was shown to enhance the selectivity and specificity. This was accomplished by merging the discharge gas with an appropriate reagent headspace vapor (e.g., from a 0.2% trifluoracetic acid solution).

Detection of explosives and related compounds by low-temperature plasma ambient ionization mass spectrometry.

A miniature mass spectrometer was modified by incorporating a conversion dynode detector system and the appropriate electronics to allow the detection of negatively charged ions. The system was fitted with a discontinuous atmospheric pressure interface to allow external ionization by desorption electrospray ionization (DESI). It was used to identify the explosives 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenyl-N-methylnitramine (Tetryl), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) present in trace amounts on surfaces (500 pg/cm2 to 1 μg/cm2) both individually and as components of mixtures. Detection of explosives was demonstrated in the presence of an interfering matrix. A large surface (5 cm ×15 cm) on which 1 μg/cm2 samples of TNT, Tetryl, and HMX had been spotted randomly was interrogated in 22 s in the full scan mode, and signals characteristic of each of the explosives were observed in the DESI mass spectrum.

Detection of explosives as negative ions directly from surfaces using a miniature mass spectrometer.

Ambient ionization methods such as desorption electrospray ionization (DESI) allow the analysis of chemicals adsorbed at surfaces without the need for sample (or surface) pretreatment. A limitation of current implementations of these ionization sources is the small size of the area that can be sampled. This makes examination of surfaces of large areas time-consuming because of the need to raster across the surface. This paper describes a DESI source that produces a spray plume with an effective desorption/ionization area of 3.6 cm2, some 200 times larger than given by conventional DESI sources. Rhodamine 6G and several drugs of abuse (codeine, heroin and diazepam) were used to demonstrate the ability to use large-area DESI MS to perform rapid (a few seconds) representative sampling of areas of the order of several square centimetres without scanning the probe across the surface. The large area ion source displayed high sensitivity (limits of detection in the high nanogram range) and high reproducibility (∼20 to 35% relative standard deviation). The rapid analysis of even larger surfaces (hundreds of cm2) for traces of explosives is possible using a sorbent surface wipe followed by large-area DESI interrogation performed directly on the wipe material. The performance of this mass transfer dry wipe method was examined by determination of the limits of detection of several explosives. Surfaces with different topographies and compositions were also tested. Using this method, absolute limits of detection observed for HMX and RDX from plastic surfaces and skin were found to be as low as 10 ng cm−2. The concentration of residue from large surface areas in this technique allowed the detection of 100 ng of explosives from surfaces with areas ranging from 1.00 × 103 cm2 to 1.40 × 104 cm2.

Trace detection of non-uniformly distributed analytes on surfaces using mass transfer and large-area desorption electrospray ionization (DESI) mass spectrometry

Desorption electrospray ionization (DESI) is a droplet-based ionization method that is applied to samples in the ambient environment with little or no sample preparation. Its utility for industrial applications is explored here for the case of pharmaceutical cleaning validation. A non-proximate large-area DESI system was built to examine representative areas of the surfaces of reaction vessels used in active product ingredient (API) manufacturing. A large-area sprayer capable of sampling an area of ∼2.5 cm2 was coupled with a transport tube to allow sensitive, representative sampling of APIs from a stainless steel surface 1 m away from the mass spectrometer. The system was used to detect the APIs neostigmine, acebutolol, amiloride, amiodarone, ibuprofen, montelukast, potassium clavulanate, and β-estradiol, at levels as low as 30–10 ng/cm2, easily satisfying the general acceptable limits set by the pharmaceutical industry. These levels were achieved from surfaces resembling the equipment used in API manufacturing processes at a rate of 30 s per analysis. Copyright © 2008 John Wiley & Sons, Ltd.

Pharmaceutical cleaning validation using non-proximate large-area desorption electrospray ionization mass spectrometry.

https://nsuworks.nova.edu/cgi/viewcontent.cgi?article=1189&context=cnso_chemphys_facarticles

Gary A. Salazar

Papers

Detection of explosives and related compounds by low-temperature plasma ambient ionization mass spectrometry.

Detection of explosives as negative ions directly from surfaces using a miniature mass spectrometer.

Trace detection of non-uniformly distributed analytes on surfaces using mass transfer and large-area desorption electrospray ionization (DESI) mass spectrometry

Pharmaceutical cleaning validation using non-proximate large-area desorption electrospray ionization mass spectrometry.

Rephasing ion packets in the orbitrap mass analyzer to improve resolution and peak shape