Nano APCI

Raterink, R.J., de Korte, M., van der Linden, H., Hankemeier, T. (2010) Chip-based Heaterless Nano-APCI-MS. 14th International Conference on Miniaturized Systems for Chemistry and Life Sciences, October 3-7, 2010, Groningen. 

ESI and APCI are soft ionisation techniques which usually result in quasi-molecular ions such as [M + H]+ with little or no fragmentation molecular weight information can easily be obtained. However, experimental conditions can also be chosen in such a way that a sufficiently characteristic pattern is obtained, allowing verification [540]. ESI is amenable to thermally labile and nonvolatile molecules. Both ESI and APCI are much more sensitive than PB and very well suited for quantitative analysis, but less so for unknown samples. The choice among the two is usually determined by the application. Recently, nanoscale LC-ESI-MS has been developed [541]. The nano-electrospray ion source offers the highest sensitivity available for LC-MS (atto-to femtomole range) and can also be used as an off-line ion source. 

The dynamic development of mass spectrometry has had a huge impact on lipid analysis. Currently, a variety of suitable mass spectrometers is available. In principal, a mass spectrometer consists of an ion source, a mass analyzer, and an ion detector. The typical features of each instrument (Fig. 2) result mostly from the types of ion source and mass analyzer. To date, the ionization techniques apphed to lipid analysis include Electrospray Ionization (ESI or nano-ESI), Atmospheric Pressure Chemical Ionization (APCI), Matrix-Assisted Laser Desorption/Ionization... 

Farwanah H, Pierstorff B, Schmelzer CEH, Raith K, Neu-bert RHH, Kolter T, Sandhoff K. Separation and mass spec-trometric characterization of covalently bound skin ceramides using LC/APCI-MS and nano-ESI-MS/MS. J. Chromatogr. B. 2007 852 562-570. 

The specific design of the various sample introduction devices or spray probes depends to a large extent on the technique applied, i.e., ESI, APCI, or other. With respect to ESI, systems have been described for conventional pure ESI, pneumatically-assisted ESI or ionspray, ultrasonically-assisted ESI, thermally-assisted ESI, and micro- and nano-ESI (Ch. 5.5). The heated-nebulizer system (Ch. 5.6.2) is used in APCI and atmospheric-pressure photoionization (APPI). 

From a practical point of view, the discussion on flow-rate can be summarized as follows. In LC-APCI-MS, the typical flow-rate is 0.5-1.0 ml/min. For routine applications of LC-ESI-MS in many fields, extreme column miniaturization comes with great difficulties in sample handling and instrument operation. In these applications, LC-MS is best performed with a 2-mm-ID column, providing an optimum flow-rate of 200 pFmin, or alternatively with conventional 3-4.6-mm-ID columns in combination with a moderate split. In sample limited cases, further reduction of the column inner diameter must be considered. Packed microcapillary and nano-LC columns with micro-ESI and nano-ESI are rontinely applied inproteomics stndies (Ch. 17.5.2). 

Some analyte fragmentation can be induced with APCI-MS and ESI-MS by collision-induced dissociation (CID) on octapole, hexapole, or cone devices at the input of the mass spectrometer. The newly developed direct electron ionization interface (DEI) involves the direct introduction of a nano-LC system working with a mobile phase flow rate of between 0.3 and 1.5 /rl/min into a mass spectrometer equipped with an electron ionization interface. It has been used to determine and identify several OPPs in water samples. Electron ionization generates spectra that can be interpreted using commercially available documentation (Wiley or NIST). 

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