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Micro and Nanopipettes for Electrochemical Imaging and Measurement
Published in Allen J. Bard, Michael V. Mirkin, Scanning Electrochemical Microscopy, 2022
Kristen Alanis, Sasha Elena Alden, Lane Allen Baker, Edappalil Satheesan Anupriya, Henry David Jetmore, Mei Shen
Local electrochemical analysis with complimentary MS for product quantification is a promising future for scanning droplet-contact methods.18 In addition to the soft push-pull SECM method previously described, glass pipettes utilized as push-pull probes have been used to collect, deliver and subsequently analyze products by MS from local electrochemical reactions.30 With advances in desorption electrospray ionization (DESI) for analysis of products from electrochemical reactions, intermediates formed on the order of milliseconds can be quantified.315–317 In one method, droplets containing an electrochemically active analyte were propelled from a spray probe at a rotating electrode covered in a thin film of electrolyte solution, termed “waterwheel” WE. After ET events were detected, droplets at the surface of the electrode and were immediately driven into an MS inlet for analysis.315,318 Scanning capabilities of DESI are continuing to improve and could one day be used in tandem with a micro or nanoscale scanning electrochemical methods for real-time, high-resolution correlative electrochemistry and MS analysis imaging.316,319
Emerging Biomedical Analysis
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
Many variants of ESI have been developed in recent years. Ambient ionization is a family of techniques that was derived from ESI to enable rapid MS analysis at lower cost. Ambient ionization techniques generate ions under ambient conditions for subsequent MS analysis directly on the sample with minimum sample preparation (Cooks et al. 2006, Nyadong et al. 2007). Representative ambient ionization techniques are desorption electrospray ionization (DESI) and direct analysis in real time (DART). In the DESI technique, an electrospray of charged solvent droplets hits the sample surface and extracts analyte molecules to form secondary droplets (Fig. 2). The secondary droplets undergo a similar ionization process with ESI and eventually are delivered to the inlet of a mass spectrometer (Takats et al. 2004). In the DART methodology, an electrical potential is applied to a helium gas stream to generate metastable species. These excited-state gas molecules subsequently react with the analyte surface to form ions (Cody et al. 2005). Due to the simple and cost-effective experimental setup, DESI, DART and other ambient ionization techniques, such as paper spray ionization, liquid microjunction surface sampling probe (LMJ-SSP) and rapid evaporative ionization mass spectrometry (REIMS), were used in several clinical studies (Li et al. 2017). Examples of clinical applications of ambient ionization MS will be discussed later in this chapter.
Thin Layer Chromatography
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Łukasz Cieśla, Monika Waksmundzka-Hajnos, Joseph Sherma
The on-line TLC–MS solutions are further subdivided into vacuum-based spectrometry and ambient ionization mass spectrometry approaches. The following vacuum-based desorption/ionization techniques have been applied in direct sampling TLC–MS: fast atom bombardment (FAB), liquid secondary ion mass spectrometry (LSIMS), laser desorption/ionization (LDI), matrix-assisted laser desorption/ionization (MALDI), and surface assisted laser desorption/ionization (SALDI) (Cheng et al., 2011). The development of atmospheric pressure ionization MS can be considered as another step ahead in the development of TLC–MS hyphenation. In atmospheric pressure techniques, the TLC plate does not have to be placed in a vacuum chamber for ionization. The following techniques have been applied for the ambient ionizing of compounds adsorbed on solid surfaces: laser desorption/atmospheric pressure chemical ionization (LD/APCI), laser ablation inductively coupled plasma (LA-ICP), desorption electrospray ionization (DESI), direct analysis in real time (DART), electrospray laser desorption ionization (ELDI), and laser-induced acoustic desorption/electrospray ionization (LIAD/ESI) (Cieśla and Kowalska, 2013).
Detection of RDX traces at the surface with sonic aerosol flow desorption
Published in Aerosol Science and Technology, 2018
Viktor V. Pervukhin, Yuri N. Kolomiets
The search for ways to simplify the preparation of samples led to the development of a number of methods, commonly called ambient mass spectrometry (Monge et al. 2013). These methods, in which analyte ions are formed by the action of charged droplets, particles, ions, or metastable atoms on the surface, include: Desorption Electrospray Ionization (DESI, Cotte-Rodriguez et al., 2005; Cotte-Rodríguez and Cooks 2006; Takáts et al. 2005; Justes et al. 2007), Direct Analysis in Real Time (DART, Petucci et al. 2007; Cody, Laramée, and Durst 2005), and Desorption Atmospheric Pressure Chemical Ionization (DAPCI, Chen et al. 2007). The methods have a great potential for analyzing surfaces, as they bypass the stage of sample preparation. However, since the MS is used as an analyzer, the methods become expensive and not always applicable in the field. On the other hand, the DESI simulation shows that the hydrodynamic forces play an important role in the desorption of the analyte from the surfaces in this process (Costa and Cooks 2008). Therefore, it seems reasonable to separate desorption and analysis in this case. Such approach allows collecting microparticles without manual sampling and using a simple device for analysis (e.g., gas chromatograph).