Paper spray ionization

Sukumar, H. Stone, J.A. Nishiyama, T. Yuan, C. Eiceman, G.A., Paper spray ionization with ion mobility spectrometry at ambient pressure, Int. J. Ion Mobil. Spectrom. 2011, 14,51-59. 

Liu, W., Wang, N., Lin, X., Ma, Y., Lin, J.-M. (2014) Interfacing Microsampling Droplets and Mass Spectrometry by Paper Spray Ionization for Online Chemical Monitoring of Cell Culture. Anal. Chem. 86 7128-7134. 

Salentijn, G.I.J., Permentier, H.P, Verpoorte, E. (2014) 3D-Printed Paper Spray Ionization Cartridge with Fast Wetting and Continuous Solvent Supply Features. Anal. Chem. 86 11657-11665. 

By combining microdialysis with nanoESI-MS, low-volume, low-concentration releases of small proteins in a three-dimensional neural cell culture system could be detected [78]. While microdialysis removes interferents, it also has an effect on the temporal resolution of the device ( 1 min). Alternatively, a microdialysis probe can be coupled with paper-spray ionization MS which enables the monitoring of glucose in a cell culture medium [79]. 

Methods Ambient ionization methods, of which there are now over 20, e.g., desorption electrospray ionization (DESI), desorption atmospheric pressure chemical ionization (DAPC), desorption atmospheric pressme photo-ionization (DAPPI), and direct analysis in real time (DART), are now joined by paper spray, a method where ESI is initiated at the pointed tip of a piece of filter paper. A drop of blood ( 15 pi) is dried on the paper, and then the paper is moistened with 25 pi of a solvent suited to both the extraction of the analytes from the blood and the ESI process (e.g., 90% methanol 10% water with either 100 ppm acetic acid or 200 ppm sodium acetate). When the paper is exposed to high voltage (3-5 kV) while held close ( 5 mm) to the entrance of the mass analyzer, a spray (similar to electrospray) is induced at the tip of the paper as capillary action carries extracted compounds through the paper (Figure 4.5). The spray is maintained for 30-90 s at a flow rate comparable to that used in nano-electrospray. 

In another application, paper used to wipe a surface contaminated with heroin and cocaine was cut to provide the necessary emission point both drugs were detected. Paper spray was also shown to ionize various other compounds effectively, including methyl violet (a dye), phosphatidylcholine (a lipid), angiotensin (a peptide), and the protein cytochrome C. 

Desorption electrospray ionization was implemented on this portable mass spectrometer [23], DESI experiments were carried out at ambient capillary temperature, at a spray voltage of 3kV and a nebulizing N2 gas flow of 80-120 psi. Detection of RDX from three different surfaces (paper, plastic, and metal) was demonstrated with this portable instrument in the positive-ion mode, with an analysis time of 5-10 s. The result obtained for 10 ng of RDX deposited on 1-cm2 paper is shown in Fig 11(a). Figure 11(b) shows... 

Desorption electrospray ionization (DESI), an ambient MS technique, was used for trace detection of the explosive RDX, directly from a wide variety of surfaces (metal, plastic, paper, polymer) without sample preparation or pretreatment. Increased selectivity was obtained both by MS/MS and by performing additional experiments in which additives were included in the spray solvent. Pure water could be used as the spray solution for DESI, and it showed ionization efficiencies for RDX in the negative ion mode similar to those given by methanol/water <2005ANC6755>. 

Like DART, DESI has received widespread acceptance as evidenced by more than 750 papers and conference presentations till mid-2014, referring to the technique since its introduction in 2004 by Cooks and coworkers [195, 196]. The technique makes use of electrospray ionization (ESI) that is widely used in the mass spec-trometiy of larger molecules in which a solution is nebulized to create a fine spray of very small droplets. In DESI, a standard electrospray of charged droplets hits the surface where the molecules of interest are present or adsorbed (including larger biomolecules), detaches them from the siuface, and delivers them as desolvated ions in the mass spectrometer. DESI is thus similar to DART (Sect. 8.4) where the gaseous plasma of ions from the ion source desorbs molecules from a surface. A schematic diagram of the main aspects of a DESI ion source is shown in Fig. 8.9. 

The combination of HPLC separation and MS is described in several papers and the number of applications where HPLC-MS is used is rapidly increasing with the availability of less-expensive benchtop instruments. The superiority of the mass spectrometer compared to other HPLC detectors is imdisputed, for it offers unsurpassed selectivity and also, to some degree, structure identification, thus being a powerful tool for the characterization of complex water samples. Several ionization techniques, such as atmospheric pressure chemical ionization (APCI), electrospray/ion spray (ESP/ISP), and thermospray (TSP) [76], have been employed in the MS determination of phenols at low concentration. 

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