DESI mechanism

Z. Takats, J. M. Wiseman and R. G. Cooks, Ambient mass spectrometry using desorption electrospray ionization (DESI) instmmentation, mechanisms and applications in forensics, chemistry, and biology, J. Mass Spectrom., 40, 1261 1275 (2005). 

R. G. Ambient mass spectrometry using desorption electrospray ionization (DESI) instrumentation, mechanisms and applications in forensics, chemistry, and biology. 

A new ionization method called desorption electrospray ionization (DESI) was described by Cooks and his co-workers in 2004 [86]. This direct probe exposure method based on ESI can be used on samples under ambient conditions with no preparation. The principle is illustrated in Figure 1.36. An ionized stream of solvent that is produced by an ESI source is sprayed on the surface of the analysed sample. The exact mechanism is not yet established, but it seems that the charged droplets and ions of solvent desorb and extract some sample material and bounce to the inlet capillary of an atmospheric pressure interface of a mass spectrometer. The fact is that samples of peptides or proteins produce multiply charged ions, strongly suggesting dissolution of the analyte in the charged droplet. Furthermore, the solution that is sprayed can be selected to optimize the signal or selectively to ionize particular compounds. 

You haye been usii pens and mechanical pencils for many years now. Invesdgate the design of at least five different pens and mechanical pencils. Discuss what you think are important desi parameters. Discuss the advantage and disadvantage associated with each des n. Write a brief report explaining your findings. 

Takats, Z., Wiseman, J.M., Cooks, R.G. (2005) Ambient Mass Spectrometry Using Desorption Electrospray Ionization (DESI) Instrumentation, Mechanisms and Applications in Forensics, Chemistry, and Biology. J. Mass Spectrom. 40 1261-1275. 

The product ions produced from the sodium adduct of TATP formed by ESI were similar to those previously reported to form by CID following DESI [27,51]. Low nanogram LODs have been reported for complex formation between TATP on different surfaces and a variety of cations. The CID of TATP and TrATrP were also reported to proceed by a loss of ethane for all the metal cation adducts. Ammonia led to different products, analogous to the mechanisms discussed for ESI [51]. 

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