Supersonic LC-

Isotope abundance and elemental information is exhibited in cold El mass spectra, due to the enhanced molecular ion and the ionisation of isolated molecules without Cl-type reactions. Supersonic LC-MS provides a linear response, unlike LC-PB-MS. LC-SMB-MS is expected to compete with APPI, APCI and PB LC-MS modes (Scheme 7.8 and Figure 6.4). 

Nowadays, there are two groups working constantly on the development of an efficient El-based LC-MS interface the group directed by Prof. Cappiello at the University of Urbino (Italy) who developed the Direct-EI interface, and the one directed by Prof. Amirav at Tel Aviv University (Israel) who developed the supersonic LC-MS. Each group is following a distinctive pathway to achieve this common goal. 

Another promising approach to the use of El coupled with LC is represented by the supersonic LC-MS. This interfacing mechanism was realized at Tel Aviv University by the group directed... 

FIGURE 8.12 The supersonic LC-EI-MS apparatus. (Reproduced from Amirav, A. et al., Rapid Commun. Mass Spectrom., 15, 811, 2001. Copyright 2001. With permission from Elsevier.)... 

FIGURE 8.14 A comparison of the cold El mass spectrum of corticosterone obtained with the supersonic LC-EI-MS system and its fitted NIST library mass spectrum, including the NIST library-matching factors and the probability of identification. Note the enhanced molecular ion (m/z = 346) exhibited. The NIST library-matching factors and the probability of identification are included. Corticosterone was flow injected using a 200pL/min methanol solvent flow rate with a 1 ng/pL corticosterone sample concentration. (Reproduced from Amirav, A. et al, Rapid Commun. Mass Spectrom., 15, 811, 2001. Copyright 2001. With permission from Elsevier.)... 

Enhanced molecular ion implies reduced matrix interference. An SMB-El mass spectrum usually provides information comparable to field ionisation, but fragmentation can be promoted through increase of the electron energy. For many compounds the sensitivity of HSI can be up to 100 times that of El. Aromatics are ionised with a much greater efficiency than saturated compounds. Supersonic molecular beams are used in mass spectrometry in conjunction with GC-MS [44], LC-MS [45] and laser-induced multiphoton ionisation followed by time-of-flight analysis [46]. 

Recently, a revival of electron ionisation LC-MS has been proposed by development of LC-SMB-MS [529]. In this system, the LC output (50-250 p,Lmin 1) is vaporised at atmospheric pressure and expanded from a supersonic nozzle into the vacuum system... 

The LC-MS with a supersonic molecular beam (LC-SMB-MS) apparatus, which is schematically shown in Figure 8.13, is based on a modified homemade GC-MS with an SMB system that was previously described [76]. The heart and soul of this system is the soft thermal vaporization nozzle (STVN) chamber. The STVN accepts the liquid flow from the LC or the flow injection liquid... 

Thermospray was in several ways the forerunner of electrospray and atmospheric pressure chemical ionization sources, and in current practice has largely been superseded by them. Thermospray (TSP) is a combination of interface and ion source for LC-MS and other liquid-phase sample introduction systems [7,31-33]. A continuous flow of liquid is rapidly vaporized in a resistively heated metal capillary tube forming a supersonic... 

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