Electrospray deposition interface

Applying semi-on-line coupling techniques, particularly spraying, provides reproducible results. The coupling to an electrospray deposition interface is shown in Figure 5.11. The matrix can be added to the eluent stream by an injection pump with flow rates of 5—10 pi/min" or it can be predeposited on the target in a preceding step. 

FIGURE 5.11 Electrospray deposition interface. Source Reprinted with permission from S. M. Weidner,. Falkenhagen, LC-MALDI-TOF Itmging MS A New Approach in Combining Chromatography and Mass Spectrometry of Copolymers, Analytical Chemistry, 83 (2011) 9153—9158. (2011) American Chemical Society (Ref. [126]). 

Morota, K., H. Matsumoto, T. Mizukoshi, Y. Konosu, M. Minagawa, A. Tanioka, Y. Yamagata, and K. Inoue (2004). Poly(ethylene oxide) thin films produced by electrospray deposition morphology control and additive effects of alcohols on nanostmcture. Journal of Colloid and Interface Science 279(2) 484-492. 

Matsumoto H, Wakamatsu Y, Minagawa M, Tanioka A. Preparation of ion-exchange fiber fabrics by electrospray deposition. J Colloid Interface Sci 2006 293 143-50. 

Matsumoto, H., Yako, H., Minagawa, M., and Tanioka, A. (2007) Characterization of chitosan nanofiber fabric by electrospray deposition electrokinetic and adsorption behavior. /. Colloid Interface Sci., 310, 678-681. 

An involatile ion-pairing reagent would be deposited in the electrospray interface and lead to a reduction in performance. Some interfaces have been specifically designed to minimize this by removing the line-of-sight between the spray and the entrance to the mass spectrometer, and are thus more tolerant to involatile buffers. The performance of the interface will be improved by the use of volatile alternatives. 

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

---