Best Anode Temperature and Thermal Decomposition

Example The FD spectrum of a ruthenium-carbonyl-porphyrin complex shows an isotopic pattern very close to the theoretical distribution (Chap. 3.2.8). The loss of the carbonyl ligand chiefly results from thermal decomposition. A spectmm accumulated close to BAT (scans 19-25, EHC = 25-30 mA) is nearly free from CO loss while a spectrum accumulated of scans 30-36 (35 0 mA) 

In FD mode, the sensitivity (Chap. 5.2.4) of actual magnetic sector instruments is about 4 X 10 C pg for the quasimolecular ion of cholesterol, m/z 387, at R = 1000. This is 10 times less than specified for those instruments in El mode and 10 times less than for Cl mode. 

At first sight, FI and FD produce a disadvantageous variety of ions depending on the polarity of the analyte and on the presence or absence of impurities such as alkali metal ions. However, with some knowledge of the ions formed, the signals can be deconvoluted without difficulty (Table 8.2). 

Note One alkali adduct ion almost never occurs exclusively, i.e., [Mh-H] , [MH-Na] and [Mh-K] (Mh-1, M+23 and Mh-39) are observed with varying relative intensities at 22 u and 16 u distance, respectively. This makes the recognition of those peaks straightforward and effectively assists the assignment of the molecular weight. 

The analyte may be neutral or ionic. However, anions are usually detected solely in an indirect manner, i.e., from corresponding cluster ions. Solutions containing metal salts, e.g., from buffers or excess of non-complexed metals, are to be avoided, because sudden desorption of the metal ions at higher emitter current often leads to rupture of the emitter. A mass range up to 3000 u is easily covered by FD, examples reaching up to 10,000 u have been presented. 

Example The FD spectrum of a ruthenium-carbonyl-porphyrin complex shows an isotopic pattern very close to the theoretical distribution (Chap. 3.2.8). The loss of the carbonyl ligand chiefly results from thermal decomposition. A spectrum accumulated close to BAT (scans 19-25, EHC 25-30 mA) is nearly devoid of CO loss, while a spectrum accumulated of scans 30-36 (35-40 mA) shows significant CO loss (Fig. 8.20). This is demonstrated by comparison of the total ion chromatogram (TIC) with the reconstructed ion chromatogram (RIC) of IVE and [M-CO] (Chap. 5.4). The FD spectrum of a lower-mass complex was essentially devoid of signals of CO loss because lower emitter currents were sufficient to effect desorption [117]. 

Numerous analytes could be good candidates for FD-MS, but undergo immediate decomposition by reacting with ambient air and/or water during conventional emitter loading. Emitter loading under inert conditions such as in a glove box does not really avoid the problem, because the emitter still needs to be mounted to the probe before insertion into the vacuum lock. 

The majority of LIFDI applications either deals with sensitive compounds such as transition metal conplexes [30,123,124] or belongs to the group of petroleomics applications [33,125-127]. Using an extremely low liquid flow rate even allows to continuously deliver sample solution to an emitter at high voltage, permiting continuous-flow (CF-)LIFDI experiments [34,128]. More recently, an automated LIFDI system has been introduced [129]. 

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