Nanospray electrospray ionization

Miniaturized ESI interfaces (nanospray electrospray ionization, nanoESI) match the dimensions of microfluidic chips. On-line couphng of microchips with ESI can be accomplished using different interface geometries blunt end, comer outlet, external capillary, external emitter, or monolithic emitter [27], some of which resemble the nanoESI emitters used in CE-MS (see also Chapter 6). In fact, on-chip capillary channels are often used as CE or LC separation columns, and directly linked with the nanoESI emitters. Atmospheric pressure chemical ionization (APCI) and photoionization (APPI) have also been subject to miniaturization but they have not attracted as much attention when it comes to hyphenation with microchips [28]. This situation may change when the novel nanoAPCI interfaces [29] are perfected, providing the way to transmit and ionize non-polar analytes at low flow rates. 

Many studies of biomolecules carried out by ESI-MS assume that, in the gas-phase conditions, ions retain elements of liquid-phase structures [22]. This assumption is supported by experimental results and molecular dynamics simulations. It has been suggested that solution-phase conformers of some proteins may be preserved for several tens of milliseconds after the ESI [21, 23, 24]. Because of the soft character ofESI, some protein-ligand complexes and large protein assemblies may also maintain non-covalent bonding in the gas phase [16, 24-29]. For example, nanospray electrospray ionization (nanoESI)-MS enabled the formation of complexes between a heat shock protein and an unfolding luciferase (client) to be monitored in the course of a few minutes [30]. 

The HPLC system comprised a 75 ftm x 15 cm PepMap column with a linear gradient of acetonitrile/0.1% aqueous formic acid (5 to 50% acetonitrile over 45 min) at a flow rate of 250 nlmin . Positive-ion electrospray ionization was employed using a nanospray interface. MS-MS specna were acquired over the range m/z 40 to 2000 at a rate of 1 s per scan. 

Wetterhall, M., Nilsson, S., Markides, K. E., and Bergquist, J. (2002). A conductive polymeric material used for nanospray needle and low-flow sheathless electrospray ionization applications. Anal. Chem. 74, 239-245. 

Wetterhall, M. Nillson, S. Markides, K.E. Bergquist, J. A Conductive Polymeric Material Used for Nanospray Needle and Low-Flow Sheathless Electrospray Ionization Applications, Anal. Chem. 74,239-245 (2002). 

The most common instrumentation for the analysis of biomarkers includes microbore and capillary reversed-phase chromatography coupled to a triplestage quadrupole (TSQ) mass spectrometer or ion trap, with an atmospheric pressure ionization source such as electrospray ionization (ESI), nanospray ionization (NSI), or atmospheric pressure chemical ionization (APCI). Ion trap mass spectrometers provide higher sensitivity in full-scan mode, which is useful for product ion identification of a metabolite however, TSQs are used most often due to improved sensitivity for quantification in multiple reaction... 

MS, MS/MS and MS experiments were performed with a LTQ-Orbitrap (Thermo Fisher Scientific Inc., San Jose, CA, USA) mass spectrometer equipped with a Triversa Nanomate (Advion Biosciences Inc., Ithaca, NY, USA). Compound solutions were infused with a nanospray chip. The mass spectrometer was first calibrated externally with a mixture containing caffeine, L-methionyl-arginyl-phenylalanyl-alanine (MRFA) and Ultramark 1621 in ACN, MeOH, HjO, acetic acid. Sub-ppm mass accuracy was finally achieved using an internal calibration (lock mass) in both MS and MS/MS mode. The resolution of Orbitrap MS was set to 100,000 (FWHM) at m/z 400. Electrospray ionization (ESI) was used. For MS/MS experiments, an isolation width of 1.5 Da was used. The normalized collision energy was set to the value when the precursor ion was exhausted. Helium was used as the collision gas. 

Roach, P.J., Laskin, J., Laskin, A. (2010) Nanospray Desorption Electrospray Ionization An Ambient Method for Liquid-Extraction Surface Sampling in Mass Spectrometry. Analyst 135 2233-2236. 

Figure 4.6 Online coupling of an electrochemical flow cell with nanospray desorption electrospray ionization MS. (a) Scheme showing the configuration of the EC/nanospray desorption electrospray ionization MS with an electrochemical flow cell. Nanospray desorption electrospray ionization MS spectra acquired when the dopamine solution flowed through the thin-layer electrochemical cell with an applied potential of (b) 0.0 and (c) 1.5 V. (d) EIC of m/z 152 acquired when the dopamine solution flowed through the thin-layer electrochemical cell [ 175]. Reprinted with permission from Liu, R, Lanekoff, I.T., Laskin, ]., Dewald, H.D., Chen, H. (2012) Study of Electrochemical Reactions Using Nanospray Desorption Electrospray Ionization Mass Spectrometry. Anal. Chem. 84 5737-5743. Copyright (2012) American Chemical Society...

Liu, R, Lanekoff, I.T., Laskin, J Dewald, H.D., Chen, H. (2012) Study of Electrochemical Reactions Using Nanospray Desorption Electrospray Ionization Mass Spectrometry. Anal. Chem. 84 5737-5743. 

Laskin, J., Heath, B.S., Roach, P.J., Cazares, L., and Semmes, O.J. 2012, Tissue imaging using nanospray desorption electrospray ionization mass spectrometry. Anal. Chem., 84 141-148. 

Watrous J, Roach P, Heath B, Alexandrov T, Laskin J, Dorrestein PC. Metabolic profiling directly from the petri dish using nanospray desorption electrospray ionization imaging mass spectrometry. Anal Chem. 2013 85 10835-391. 

Lanekoff I, Thomas M, Carson JP, et al. Imaging nicotine in rat brain tissue by use of nanospray desorption eleetrospray ionization mass spectrometry. Anal Chem. 2013 85 882-9. Cotle-Rodriguez I, Takats Z, Talaty N, et al. Desorption eleetrospray ionization of explosives on surfaces sensitivity and selectivity enhancement by reactive desorption electrospray ionization. Anal Chem. 2005 77 6755-64. 

In order to definitively establish that two fiber samples are of identical origin, it is i.a. necessary to demonstrate that their dye components are identical, and that those dyes are present in the same proportions in each fiber. The qualitative comparison is necessary because fiber manufacturers often use identical dyes in different proportions to create differently colored fibers. The combination of electrospray ionization mass spectrometry and tandem mass spectrometry has been shown to provide both the qualitative and quantitative information required such comparisons. The technique is sufficiently specific and sensitive to allow comparison of two fibers, one of which is available lengths of as little as one millimeter. The use of more sophisticated electrospray techniques (microspray and nanospray) would further enhance both specificity and sensitivity. 

Electrospray ionization mass spectrometry can be carried out over a wide range of flow rates. Technically, the term electrospray can be applied to any flow rate (it refers to the method of ionization), but additional terms have been coined to describe low-flow electrospray. Microspray describes electrospray conducted at intermediate flow rates ( 0.1-10pL/ min), and nanospray refers to very low flow electrospray (typically < lOOnL/min). 

A number of investigators have observed that there are differences in performance of nanospray versus electrospray ionization. The very different conditions (temperature, capillary diameter, use of nebulizer gas) typically employed for conventional and low-flow electrospray make absolute comparisons of sensitivity at widely different flow rates difficult. The current perception, however, is that very low flow rate systems have greater mass sensitivity than higher-fiow-rate systems. 

Nanospray is a miniaturized version of electrospray. In the original setup of Wilm and Mann (8) it is utilized as an off-line technique using disposable, finely drawn (1 -gm tip), metallized glass capillaries to infuse samples at 10-30 nL/min flow rates. This allows more than 50 min analysis time with just a 1-pT sample. Due to the formation of much smaller droplets and the more effective ionization, there is often no need for LC separation, since the separation is accomplished in m/z or by MS/MS. However, limited reproducibility with respect to quantification and a more complex sample preparation can be seen as drawbacks. An on-line version for hyphenation with capillary and nano-LC as well as CE (slightly modified) is now commercially available. 

Nanoelectrospray ionization (nanoESI), also known as nanospray, nanoflow electrospray, and micro-electrospray, is a low flow/high sensitivity approach to ESI. NanoESI15 is a slight variation on ESI such that the spray needle has been made very small and is positioned close to the entrance of the vacuum of the mass spectrometer and the mass analyzer (Figure 6). This greatly reduces required sample amounts allowing nanoliter flow rates and femto-mole sample consumption. The end result is increased efficiency since the flow rates for... 

Figure 14.5 Modified-ESI source for the direct infusion of undiluted ILs. A stainless steel wire is placed in the spray, leading to the optimal vaporization of the IL. Additionally, an orthogonal ESI source is used. Only a part of the IL ions is transferred into the MS, thus minimizing pollution of the source. (Modified from Dyson, R J. et al.. Direct probe electrospray (and nanospray) ionization mass spectrometry of neat ionic liquids. Chem. Commun., 2204, 2004. Reproduced by permission of the Royal Society of Chemistry.)...

Dyson, P. J. et al.. Direct probe electrospray (and nanospray) ionization mass spectrometry of neat ionic liquids. Chem. Commun., 2204, 2004. 

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