Thermospray interface filament

Thermospray interface. Provides liquid chromatographic effluent continuously through a heated capillary vaporizer tube to the mass spectrometer. Solvent molecules evaporate away from the partially vaporized liquid, and analyte ions are transmitted to the mass spectrometer s ion optics. The ionization technique must be specified, e.g., preexisting ions, salt buffer, filament, or electrical discharge. 

The next major advance in LC-MS interfacing was developed by Blakely and Vestal (55, 56). To circumvent the solvent elimination problem, Blakely et al. (55) developed the thermospray interface that operates with aqueous-organic mobile phase at typical 4.6-mm i.d. column flow rates, 1-2 mL/min. The thermospray technique works well with aqueous buffers. This feature is an advantage when the versatility of the reversed-phase mode is considered. In fact, with aqueous buffers, ions are produced when the filament is off. A recent improvement in the thermospray technique is the development of an electrically heated vaporizer that permits precise control of the vaporization (56). This... 

In thermospray interfaces, the column effluent is rapidly heated in a narrow bore capillary to allow partial evaporation of the solvent. Ionisation occurs by ion-evaporation or solvent-mediated chemical ionisation initiated by electrons from a heated filament or discharge electrode. In the particle beam interface the column effluent is pneumatically nebulised in an atmospheric pressure desolvation chamber this is connected to a momentum separator where the analyte is transferred to the MS ion source and solvent molecules are pumped away. Magi and Ianni (1998) used LC-MS with a particle beam interface for the determination of tributyl tin in the marine environment. Florencio et al. (1997) compared a wide range of mass spectrometry techniques including ICP-MS for the identification of arsenic species in estuarine waters. Applications of HPLC-MS for speciation studies are given in Table 4.3. 

The two electron-initiated ionization modes are filament-on and discharge-on ionization. In these modes, the thermospray interface is used as a solvent introduction device, providing nebulization and soft... 

In a thermospray interface (Figure 3B), the column effluent is rapidly heated in a narrow bore capillary such that partial (ca. 90%) evaporation of the solvent is achieved inside the capillary. As a result, a mist of vapour and small droplets is formed in which the heated droplets further evaporate and ions are generated, either by the thermospray ionization process based on ion evaporation or by solvent-mediated chemical ionization initiated by electrons from a heated filament or a discharge electrode. The excess vapour is pumped away directly from the ion source. 

The sensitivity of the interface is compound-dependent but generally high sensitivity is possible by using one of the ionization methods available (thermospray, filament and discharge). 

Nebulization ionization is the process involved in the analyte ionization in thermospray [16] and electrospray [17] interfacing. No primary ionization, i.e., a filament or a discharge electrode, is applied. The ionization mechanism is not fully understood (Ch. 6.3). The general understanding can be snmmarized as follows Upon nebulization, charged droplets of a few pm ID are generated. The fate of these droplets is determined by a nnmber of competing processes, the relative importance of which may dependent on the natnre of the analyte ... 

Detector MS, Finnigan MAT TSQ 700 tandem quadrupole, MAT TSP-2 interface, thermospray, selective reaction monitoring m/z 340-266, collision offset -6 V, repeller 100 V, vaporizer 130°, source 200°, filament on 200 jjuA, argon 2.5 mTerr, multiplier 1500 V, dynode 15 kV, scan time 1.20 s, MSMSC factor 10... 

The option of high flow rates, combined with TSP ionisation, helped to improve the sensitivity because of the quantitative transfer of analytes in the column effluents into the mass spectrometer. High flow rates under reversed-phase conditions (RP) as well as normal-phase separations (NP) were amenable to this interface type. Thermospray ionisation takes place by means of a solvent-mediated chemical ionisation (Cl) process, where a filament or discharge electrode is employed, or by an ionisation process which is enabled, and supported by a volatile buffer such as, for example, ammonium acetate, that is added to the eluent to improve positive ionisation. 

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