Atmospheric pressure photoionization applications

The most important techniques belonging to this class are electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and, more recently, atmospheric pressure photoionization (APPI). At present the latter does not have applications in cultural heritage, so it will be not described here. 

The two most common LG/MS interfaces used for routine quantitative analyses are APCI and APT electrospray. The principles of these techniques in direct infusion analyses have been described earlier (see Sections 3.3 and 3.4). As APTelectrospray has a broader application profile, its use is more widespread than APCI. Other configurations including El, atmospheric pressure photoionization (APPl), and thermospray interfaces with liquid chromatographs are available but are less commonly used for high throughput or routine analysis. 

Bos, S. J., Leeuwen, S. M., and Karst, U. (2006). Erom fundamentals to applications recent developments in atmospheric pressure photoionization mass spectrometry. Anal. Bioanal. Chem. 384, 85-99. 

Quenzer, T.L. Greig, M.J. Robinson, J.M. Bolanos, B. Pham, C. Atmospheric pressure photoionization mass spectrometry High throughput applications. In Lab Automation 2003 Palm Springs CA, 2003 104. 

Haapala M, Pol J, Saarela V, Arvola V, Kotiaho T, Ketola RA, Franssila S, Kauppila TJ, Kostiainen R (2007) Desorption atmospheric pressure photoionization. Anal Chem 79 7867-7872 Hsieh Y, Li F-B, Korfmacher WA (2010) Mapping pharmaceuticals in rat brain sections using MALDI imaging mass spectrometry. Methods Mol Biol 656 147-158 Hu LG, Xu SY, Pan CS, Zou HF, Jiang GB (2007) Preparation of a biochip on porous sihcon and application for label-free detection of small molecule-protein interactions. Rapid Commun Mass Spectrom 21 1277-1281... 

APCI), atmospheric pressure photoionization (APPI), and direct electron ionization (El). Sancho et al. [4] discuss the advantages and limitations of the various mass-analyzer technologies, and Anacleto et al. [5] describes the applications of various MS sources. 

Lagalante AF, Oswald TD. Analysis of polybrominated diphenyl ethers (PBDEs) by liquid chromatography with negative-ion atmospheric pressure photoionization tandem mass spectrometry (LC/Nl-APPl/MS/MS) application to house dust. Anal Bioanal Chem 2008 391(6) 2249-56. 

Desorption electrospray ionization (DESI) [1] was introduced at the end of 2004, and direct analysis in real time (DART) [2] soon after in 2005. The apparent potential of both DESI and DART in high-throughput applications soon led to the development of some derivatives with the intention to broaden the field of applications or to adapt the underlying methodology to specific analytical needs. Now, the repertoire of methods includes variations of the DESI theme such as desorption sonic spray ionization (DeSSI) [3], later renamed easy sonic spray ionization (EASI) [4] or extractive electrospray ionization (EESI) [5,6]. Then, there are the DESI analogs of APCI and APPI, i.e., desorption atmospheric-pressure chemical ionization (DAPCI) [7,8] and desorption atmospheric pressure photoionization (DAPPI) [9]. 

Currently, there are four commercial companies offering handheld and portable gas phase time-of-flight ion mobility spectrometers, with drift tubes shorter than 5 cm Smiths Detection, Bruker-Daltonics, GE-Interlogix, and G.A.S. Gesellschaft fiir analytische Sensorsysteme mbH. Table 1 presents their respective instruments and their major applications. These instruments generally use an applied electric field of around 250 Vcm , and they operate at either ambient or elevated temperature and at atmospheric pressure. The samples are ionized by radioactive nickel-63 source mostly but also by corona discharge and photoionization source. 

In terms of the hardware, TRMS methods described in this book use most common types of ion sources and analyzers. Electrospray ionization (ESI), electron ionization (El), atmospheric pressure chemical ionization (APCI), or photoionization systems, and their modified versions, are all widely used in TRMS measurements. The newly developed atmospheric pressure ionization schemes such as desorption electrospray ionization (DESI) and Venturi easy ambient sonic-spray ionization (V-EASI) have already found applications in this area. Mass analyzers constitute the biggest and the most costly part of MS hardware. Few laboratories can afford purchasing different types of mass spectrometers for use in diverse applications. Therefore, the choice of mass spectrometer for TRMS is not always dictated by the optimum specifications of the instrument but its availability. Fortunately, many real-time measurements can be conducted using different mass analyzers equipped with atmospheric pressure inlets - with better or worse results. For example, triple quadrupole mass spectrometers excel at quantitative capabilities however, in many cases, popular ion trap (IT)-MS instruments can be used instead. On the other hand, applications of TRMS in fundamental studies often require a particular type of instrument (e.g., Fourier transform ion cyclotron resonance mass spectrometer for photodissociation studies on trapped ions). 

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