Electrospray ionization instruments

Schematic diagram of an orthogonal Q/TOF instrument. In this example, an ion beam is produced by electrospray ionization. The solution can be an effluent from a liquid chromatography column or simply a solution of an analyte. The sampling cone and the skimmer help to separate analyte ions from solvent, The RF hexapoles cannot separate ions according to m/z values and are instead used to help confine the ions into a narrow beam. The quadrupole can be made to operate in two modes. In one (wide band-pass mode), all of the ion beam passes through. In the other (narrow band-pass mode), only ions selected according to m/z value are allowed through. In narrow band-pass mode, the gas pressure in the middle hexapole is increased so that ions selected in the quadrupole are caused to fragment following collisions with gas molecules. In both modes, the TOF analyzer is used to produce the final mass spectrum.

Cole, R.B., Electrospray Ionization Mass Spectrometry Fundamentals, Instrumentation and Applications, Wiley, Chichester, U.K., 1997. 

Cole R. B. (Ed.), Electrospray Ionization Mass Spectrometry - Fundamentals, Instrumentation... 

As with GC/MS, LC/MS offers the possibility of unequivocal confirmation of analyte identity and accurate quantiation. Similarly, both quadrupole and ion-trap instruments are commercially available. However, the responses of different analytes are extremely dependent on the type of interface used to remove the mobile phase and to introduce the target analytes into the mass spectrometer. For pesticide residue analyses, the most popular interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Both negative and positive ionization can be used as applicable to produce characteristically abundant ions. 

Wang, G. Cole, R. B. In Electrospray Ionization Mass Spectrometry Fundamentals Instrumentation and Applications. Cole, R. B. (Ed.). New York Wiley, 1997, pp. 137-174. 

Z. Takats, J. M. Wiseman, and R. G. Cooks. Ambient Mass Spectrometry Using Desorption Electrospray Ionization (DESI) Instrumentation, Mechanisms and Applications in Forensics, Chemistry, and Biology. J. Mass Spectrom., 40(2005) 1261-1275. 

There are many reviews on specific MS or ionization techniques that will be referenced in the following sections, but electrospray is one of the newest ionization methods that are fast becoming an important technique in inorganic and organometallic chemistry. A review (17) on electrospray applied to inorganic and organometallic chemistry appeared in 1995 and the rapid growth of this area probably warranted another review (18). A useful book entitled Electrospray Ionization Mass Spectrometry, Fundamentals, Instrumentation, and Applications has... 

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 - ). 

Electrospray Ionization Mass Spectrometry - Fundamentals, Instrumentation and Applications 1st ed. Dole, R.B., editor John Wiley Sons Chichester, 1997. Fenn, J.B. Electrospray Wings for Molecular Elephants (Nobel Lecture). Angew. Chem., Int. Ed. 2003, 42, 3871-3894. Fuerstenau, S.D. Benner, W.H. Molecular Weight Determination of Megadalton DNA Electrospray Ions Using Charge Detection Time-of-Flight-MS. Rapid Commun. Mass Spectrom. 1995, 9, 1528-1538. 

In general the commercial TOP instruments have two detectors one for the linear mode and one for the reflectron mode. The combination of MALDI with TOP is ideal because both techniques are pulsed techniques. However, it is also possible to arrange a continuous beam as generated by electrospray ionization. Por that purpose orthogonal acceleration was developed [65]. The ion beam is introduced perpendicularly to the TOP and packets are accelerated orthogonally (oa-TOP) at similar frequencies improving the sensitivity. While a packet of ions is analyzed, a new beam is formed in the orthogonal acceleration. 

R. G. Ambient mass spectrometry using desorption electrospray ionization (DESI) instrumentation, mechanisms and applications in forensics, chemistry, and biology. 

Jorgensen, T. J. D., Hvelplund, P., Andersen, J. U., Roepstorff, P. Tandem mass spectrometry of specific vs. nonspecific noncovalent complexes of vancomycin antibiotics and peptide ligands. Int J Mass Spectrom 2002, 219, 659-670. Tahallah, N., Pinkse, M., Maier, C. S., Heck, A. J. The effect of the source pressure on the abundance of ions of noncovalent protein assemblies in an electrospray ionization orthogonal time-of-fiight instrument. Rapid... 

A home-built spray ion source, operable in both the sonic-spray ionization (SSI) and electrospray ionization (ESI) modes, was used instead of the standard ESI source of the Einnigan LCQ instrument. (Erom Takats et al., 2003b)... 

General Methods. The instrument that will be used to execute the gas-phase experimental portion of the proposed research is a Finnigan 2001 dual-cell Fourier transform ion cyclotron resonance mass spectrometer (FTMS or FTICR), equipped with both electron impact (FI) and electrospray ionization (FSl). FTMS is a high-resolution, high-sensitivity technique that allows the entrapment and detection of gas-phase species. Gas-phase ions are trapped in a magnetic field, much like a reactant sits in a flask in solution. The instrument is a mass spectrometer therefore, we will often refer to the mass-to-charge (m/z) ratio of ions, which is the method we use to identify species. (M-l) or (M-H) refers to a molecule M that has been deprotonated for example, HjO has an (M-f) ion of m/z 17 (HO ). 

R.B. Cody, Electrospray ionization mass spectrometry History, theory, and instrumentation. In B.N. Pramanik, A.K. Ganguly, M.L. Gross (Eds.) Applied Electrospray Mass Spectrometry, Marcel Dekker, Inc., New York, 2002, pp. 1-104. 

G. Wang, R.B. Cole, Solution, gas-phase, and instrumental parameter influences on charge-state distributions in electrospray ionization mass spectrometry. In R.B. Cole (Ed.) Electrospray Ionization Mass Specrmmerty, Wiley, New York, 1997, pp. 137-174. 

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