Ion Sources for ESI

Micromass Quatro II triple stage quadrupole fitted with an electrospray ion source for ESI MS and ESI MS/MS (MRM mode) analysis... 

Polymeric microfluidic systems coupled to a microfabricated planar polymer tip can be used as a stable ion source for ESI-MS. A parylene tip at the end of the microchannel delivers fluid which easily produces a stable Taylor cone at the tip via an applied voltage. The described device appears to facilitate the formation of a stable spray current for the electrospray process and hence offers an attractive alternative to previously reported electrospray emitters. When this interface was employed for the quantification of methylphenidate in urine extracts via direct infusion MS analysis, this system demonstrated stable electrospray performance, good reproducibility, a wide linear dynamic range, a relatively low limit of quantification, good precision and accuracy, and negligible system carryover. We believe polymeric devices such as described in this report merit further investigation for chip-based sample analysis employing electrospray MS in the future. 

Applied Biosystems Q q TOF analyser equipped with a nanoelectrospray ion source for nano ESI MS and nano ESI MS/ MS analysis... 

Pulsed ion sources for axial injection such as MALDI and SIMS, and earlier plasma desorption are suitable for TOF analyzers. For continuous ion sources such as ESI the oa configuration is suitable. 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

The TOF mass analyser requires high-frequency (kHz) pulsed ion introduction (Ch. 2.4.3). For optimum mass resolution, orthogonal acceleration is preferred. Boyle et al. [109] first reported an API ion source for a linear TOF analyser via the on-axis ESI source from Analytica of Branford. Later, orthogonal acceleration and a reflectron TOF analyser was applied [110]. Similar systems were subsequently described by others. 

The AP MALDI PDF+ ion source can be flanged to the atmospheric pressure interface (API) of ion trap-, ion trap-Orbitrap-, or bench-top Orbitrap instruments. The ion source is equipped with a frequency-tripled Nd YAG laser operating at 355 nm with 3 ns pulse duration, while the laser beam is typically coupled into a 400 pm core diameter fiber forming a spot size of 500 x 600 pm on the plate (a smaller-diameter fiber can also be applied). The ease-of-use of this ion source for regular MALDI applications, and the possibility ofa rapid source exchange between MALDI and ESI, have led to this source becoming an excellent tool for today s analytical studies. Details on the coupling of this source with the Exactive series instrumentation are available from the manufacturer. 

It is a universal and versatile interface to any given HPLC-MS system and can be installed to various ion sources, for example, ESI, APCI, APPI, inductively coupled plasma (ICP), and MALDI. After collection in... 

At the same time, mass spectrometry offered exquisite details on the mass and structure of small (<5000 Da) molecules but was unable to efficiently ionize larger ones. The dilemma of the mid-1980s is illustrated in Fig. 1. The results of a two-dimensional gel electrophoresis separation of kidney proteins showed a wealth of information in the >5000 Da range. Results from mass spectrometry, however, left off all molecular species in this region. The lack of efficient ion sources for these molecules started a decade-long race to produce gas-phase ions from ever larger molecules. This quest culminated in the discovery of electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) by the end of the decade. Almost overnight, molecules with masses in excess of 100 kDa could be studied by... 

The minimal in-source CID inherent in the ion source of ESI not only dramatically enhances the ionization sensitivity of ESI/MS, but also makes ESI/MS a powerful tool for quantitative applications since colUsion-induced fragmentation is a process that depends on the molecular structure of the analytes. Accordingly, ESI has currently become the method... 

Table 6 List of ions monitored for imidazolinone herbicides using in-source CID (HPLC/ESI-MS)...

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

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