Electrospray micro

Liu S, Sjovall J, Griffiths WJ. 2001. Analysis of neurosteroids in brain by nanoscale capillary liquid chromatography/ micro-electrospray mass spectrometry. J Am Soc Mass Spectrom 14 390-400. 

R. H. Negative ionization micro electrospray mass spectrometry of oligodeoxyribonucleotides and their complexes. Rapid Commun Mass Spectrom 1996, 10, 47-50. 

EM Javerfalk, A Amini, D Westerlund, PE Andren. Chiral separation of local anaesthetics by a capillary electrophoresis/partial-filling technique coupled online to micro-electrospray mass spectrometry. J Mass Spectrom 33 183-186, 1998. 

Appropriate modifications of the capillary allow the nebulization at flow rates lower than 1 pL/ min (nano and micro electrospray). As reported in Table 8.1, the electrospray can be successfully used at different flow rates, accomplishing hyphenation with LC and CE. 

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... 

M. R. Emmet and R. M. Caprioli, Micro-electrospray mass spectrometry Ultra-high-sensi-tivity analysis of peptides and proteins, J. Am. Soc. Mass Spectrom., 5 (1994) 605-613. 

PE Andren, RM Caprioli. In vivo metabolism of substance P in rat striatum utilizing microdialysis/liquid chromatography/micro-electrospray mass spectrometry. J Mass Spectrom 30 817—824, 1995. 

Emmett, M.R. Caprioli, R.M. Micro-Electrospray Mass Spectrometry Ultra-High-Sensitivity Analysis of Peptides and Proteins, J. Am. Soc. Mass Spectrom. 5,605-613(1994). 

Shimoyama, M., Tatsuoka, H., Ohtori, S., Tanaka, K. and Shimoyama, N., Change of dorsal horn neurochemistry in a mouse model of neuropathic cancer pain. Pain, 114, 221-230 (2005). Andr6n, P.E. and Caprioli, R.M., In vivo metabolism of substance-P in rat striatum utilizing in vivo microdialysis liquid chromatography— micro-electrospray mass spectrometry. J. Mass Spectrom., 30, 814-824 (1995). 

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

The ionspray (ISP, or pneumatically assisted electrospray) LC-MS interface offers all the benefits of electrospray ionisation with the additional advantages of accommodating a wide liquid flow range (up to 1 rnl.rnin ) and improved ion current stability [536]. In most LC-MS applications, one aims at introducing the highest possible flow-rate to the interface. While early ESI interfaces show best performance at 5-l() iLrnin, ion-spray interfaces are optimised for flow-rates between 50 and 200 xLmin 1. A gradient capillary HPLC system (320 xm i.d., 3-5 xLmin 1) is ideally suited for direct coupling to an electrospray mass spectrometer [537]. In sample-limited cases, nano-ISP interfaces are applied which can efficiently be operated at sub-p,Lmin 1 flow-rates [538,539]. These flow-rates are directly compatible with micro- and capillary HPLC systems, and with other separation techniques (CE, CEC). 

The mass spectrometer is a very sensitive and selective instrument. However, the introduction of the eluent into the vacuum chamber and the resulting significant pressure drop reduces the sensitivity. The gas exhaust power of a normal vacuum pump is some 10 ml min-1 so high capacity or turbo vacuum pumps are usually needed. The gas-phase volume corresponding to 1 ml of liquid is 176 ml for -hexane, 384 ml for ethanol, 429 ml for acetonitrile, 554 ml for methanol, and 1245 ml for water under standard conditions (0°C, 1 atmosphere). The elimination of the mobile phase solvent is therefore important, otherwise the expanding eluent will destroy the vacuum in the detector. Several methods to accomplish this have been developed. The commercialized interfaces are thermo-spray, moving-belt, electrospray ionization, ion-spray, and atmospheric pressure ionization. The influence of the eluent is very complex, and the modification of eluent components and the selection of an interface are therefore important. Micro-liquid chromatography is suitable for this detector, due to its very small flow rate (usually only 10 p min - ). 

Wang C., Oleschuk R., Ouchen F., Li J., Thibault R, and Harrison D.J. (2000), Integration of immobilized trypsin bead beds for protein digestion within a micro-fluidic chip incorporating capillary electrophoresis separations and an electrospray mass spectrometry interface, Rapid Commun. Mass Spectrom. 14(15), 1377-1383. 

Utilization of capillary columns in conjunction with micro ESI devices is becoming a new trend in the field of LC/MS. Capillary HPLC has become a particularly important technique in situations where the supply of analyte is limited, such as in proteomic analysis. According to studies conducted by Smith et al., only one in a hundred thousand of analyte molecules present in solution eventually reach mass detection in a conventional ESI interface. Smith et al. attributed this poor electrospray... 

Sabatini, L., Barbieri, A., Tosi, M., Roda, A., and Violante, F. S., A method for routine quantitation of urinary 8-hydroxy-2 -deoxyguanosine based on solid-phase extraction and micro-high-performance hquid chromatography/electrospray ionization tandem mass spectrometry, Rapid Communications in Mass Spectrometry 19(2), 147-152, 2005. 

For the determination of organotin compounds (tributyltin, triphenyltin, triethyltin, and tetra-ethyltin) a MAE is proposed before the normal phase (NP) HPLC/UV analysis [35], In organotin and arsenic speciation studies, hydride generation is the most popular derivatization method, combined with atomic absorption and fluorescence spectroscopy or ICP techniques [25,36], Both atmospheric pressure chemical ionization (APCI)-MS and electrospray ionization ESI-MS are employed in the determination of butyltin, phenyltin, triphenyltin, and tributyltin in waters and sediments [37], A micro LC/ESI-ion trap MS method has been recently chosen as the official EPA (Environmental Protection Agency) method (8323) [38] it permits the determination of mono-, di-, and tri- butyltin, and mono-, di-, and tri-phenyltin at concentration levels of a subnanogram per liter and has been successfully applied in the analysis of freshwaters and fish [39], Tributyltin in waters has been also quantified through an automated sensitive SPME LC/ESI-MS method [40],... 

EPA Method No 8323 Determination of organotins by micro-liquid chromatography-electrospray ion trap mass spectrometry. 

The development of mass spectrometric ionization methods at atmospheric pressures (API), such as the atmospheric pressure chemical ionization (APCI)99 and the electrospray ionization mass spectrometry (ESI-MS)100 has made it possible to study liquid-phase solutions by mass spectrometry. Electrospray ionization mass spectrometry coupled to a micro-reactor was used to investigate radical cation chain reaction is solution101. The tris (p-bromophenyl)aminium hexachloro antimonate mediated [2 + 2] cycloaddition of trans-anethole to give l,2-bis(4-methoxyphenyl)-3,4-dimethylcyclobutane was investigated and the transient intermediates 9 + and 10 + were detected and characterized directly in the reacting solution. However, steady state conditions are necessary for the detection of reactive intermediates and therefore it is crucial that the reaction must not be complete at the moment of electrospray ionization to be able to detect the intermediates. 

Micro- and nano-HPLC systems (Fig. 15.11) rely on small-diameter and capillary columns packed with high-efficiency packing materials and very slow flow rates to produce concentrated solutions and sharp chromatography peaks to feed electrospray interfaces for mass spectrometers. 

Raynor, M.W., Dawson, G.D., Balcerzak, M., Pretorius, W.G. and Ebdon, L. (1997) Electrospray nebulisation interface for micro-high performance liquid chromatography inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom., 12, 1057-1064. 

Licklider, L. Wang, X.-Q. Desai, A. Tai, Y.-C. Lee, T. D. 2000. A micro-machined chip-based electrospray source for mass spectrometry. Anal. Chem., 72,367-375. 

The first mode to interface the sample effluent from a microchip to a mass spectrometer (MS) was based on electrospray ionization (ESI). For electrospray generation, a sharp tip is usually used as an emitter. For instance, a sheath flow micro-ion sprayer was used to interface a microchip to a mass spectrometer (see Figure 7.30). CE separation was first carried out, and then the separated components were transferred to the mass spectrometer for MS analysis [812]. 

Wen, J., Lin, Y.H., Xiang, F., Matson, D.W., Udseth, H.R., Smith, R.D., Micro-fabricated isoelectric focusing device for direct electrospray ionization-mass spectrometry. Electrophoresis 2000, 21, 191-197. 

Lazar, L.M., Karger, B.L., Microchip integrated analysis systems for electrospray analysis of complex peptide mixtures. Micro Total Analysis Systems, Proceedings 5th lTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 219-221. 

Svedberg, M., Veszelei, M., Axelsson, J., Vangbo, M., Nikolajeff, F., Fabrication of open PDMS electrospray tips integrated with microchannels using replication from a nickel master. Micro Total Analysis Systems 2003, Proceedings 7th pTAS Symposium, Squaw Valley, CA, Oct. 5-9, 2003, 375-378. 

---