Thermospray positive-ion

A typical thermospray ionization mass spectrum for a sulfonylurea contains a weak protonated molecular ion and three to four characteristic fragment ions. Figure 2 shows the thermospray positive ion mass spectrum for HARMONY. The spectrum contains a protonated molecular ion at m/z 388, the sulfonamide ammonium adduct ion at m/z 239 and the protonated triazine urea fragment ion at m/z 184. At the same time, Figure 3 shows the positive ion thermospray mass spectrum for LONDAX. It contains the protonated pyrimidine amine at m/z 156, the protonated pyrimidine urea is at m/z 199 and the sulfonamide ammonium adduct ion at m/z 247. LONDAX (bensulfuron methyl) is a sulfonylurea rice herbicide and it elutes between EXPRESS and CLASSIC if we use the LC conditions outlined in Figure 1. HARMONY and LONDAX thermospray spectra were generated with the thermospray vaporizer tip temperature at 150°C and the source block temperature at 320°C. 

Figure 2. The thermospray positive ion mass spectrum of HARMONY.

Thermosprav Operation. Figures 2 and 3 show the thermospray positive ion mass spectra of HARMONY and LONDAX. The spectra contain three to four structurally informative ions. For quantitation at the method detection level in each case, we selected the most intense ions. 

Most of the ions produced by either thermospray or plasmaspray (with or without the repeller electrode) tend to be very similar to those formed by straightforward chemical ionization with lots of protonated or cationated positive ions or negative ions lacking a hydrogen (see Chapter l).This is because, in the first part of the inlet, the ions continually collide with neutral molecules in the early part of their transit. During these collisions, the ions lose excess internal energy. 

As with conventional Cl, this is a very mild form of ionization leading to molecular species with little or no fragmentation, i.e. (M + H)+ and (M — H) . This is not, however, always the case. The use of chromatographic modifiers may change the composition of the Cl plasma to such a state that, as in Cl and thermospray, other ions may be formed, e.g. the presence of ammonium acetate may lead to (M - - NH4)+ and (M - - CHsCOO)" ions in the positive- and negative-ion modes, respectively. The chemistry of the analyte may also have an effect, as has been discussed for ESI, with, for example, the spectra of fullerenes extracted from soot particles yielding an M+ molecular species [16],... 

Figure 6.10 Production of positive ions by thermospray ionisation. After Ashcroft [35]. From A.E. Ashcroft, Ionization Methods in Organic Mass Spectrometry, The Royal Society of Chemistry, Cambridge (1997). Reproduced by permission of The Royal Society of Chemistry...

MS, Mass spectrometry El, electron impact Cl, chemical ionization MID, multiple ion detection PICI, positive-ion chemical ionization NICI, negative-ion chemical ionization SIM, selected ion nmonitoring TSP, thermospray PPINICI, pulsed positive ion-negative ion chemical ionization ECD, electron-capture detector NPD, nitrogen/phosphorous detector NSTD, nitrogen-selective thermionic detector FT-IR, Fourier transform infrared spectrometry. 

Coupling of liquid chromatography with mass spectrometry can provide unequivocal on-line spectrometric identification of anthelminthic residues in animal-derived foods. Typical applications of such techniques include the confirmation of moxidectin residues in cattle fat by liquid chromatography-thermospray mass spectrometry (352), and the confirmation of eprinomectin residues in bovine liver tissue by liquid chromatography, electrospray ionization, and multiple reaction monitoring in the MS-MS mode with positive ion detection (370). 

The coupling of HPLC to a mass spectrometer (MS) has provided for the ultimate in detection systems in terms of sensitivity and versatility. Betourski and Ballard (227) have used the techniques of thermospray TSP-LC-MS and tandem LC-MS-MS to obtain positive-ion mass spectra of two cationic dyes, Basic red 14 and Basic orange 14. According to Yinon et al. (228), TSP-LC-MS has been found to be a suitable technique for the analysis of dyes. It is sensitive and specific, and the ionization process is soft. One of the drawbacks, however, is that one obtains... 

A simple assay was used for the separation and MS detection of TMP in tissue. The frozen pulverized tissue sample was homogenized with chloroform acetone, and the extract was evaporated. The residue was dissolved with MeOH acetic acid, and lipids were removed by washing with hexane. An aqueous layer was injected, and TMP was detected and identified using a thermospray LC-MS system. The MS detection was accomplished in the positive-ion mode with SIM of the ion m/z 291 (178). 

For the confirmation of PMFs in Valencia orange peel oil and juice, an HPLC method coupled with a thermospray mass spectrometry (HPLC-TSP-MS) detection system was utilized (112). A C 8 column (/zBondapak, 300 X 6-mm ID) was used with a mobile phase of H20-ACN (60 40, v/v) at a flow rate of 1.0 ml/min. Extract (20 fi1) was injected into the HPLC-TSP-MS system, and positive-ion spectra from m/z 100 to 700 were recorded at 1360 ms. Mass spectro-metric identification was done using positive chemical ionization (ICP). This technique allowed confirmation of the presence of eight flavones in the peel oils and seven flavones in the juice. 

Diagram of a thermospray source. The chromatographic effluent comes in at (a) the transfer line is suddenly heated at (b) and the spray is formed under vacuum at (c). At (d) the spray goes between a pusher with a positive potential and a negative cone for positive ions. The ions are thus extracted from the spray droplets and accelerated towards the spectrometer (f). At (e), a high-capacity pump maintains the vacuum. 

This approach was pioneered by Hayward et al. [2] for the automated analysis of potential agricultural chemicals by means of eoluttm-bypass thermospray (TSP) MS-MS. The method was found to provide the required information in approximately 70% of the MS stmetural confirmations performed at the Agricultural Research Division of American Cyanamid. Subsequently, an automated routine MS eharaeterization of potential drug eompounds was reported by Tiller and Lane [3] at Glaxo. Both particle-beam (PBl) in positive-ion chemical ionization (Cl) mode and TSP interfaeing were investigated. The TSP system was found to be more robust, to require less maintenance, and to be easier to use. 

Under thermospray LC-MS conditions, thermally-induced hydrolytic ringopening of the betalactam ring was observed, followed by the loss of COj [16]. This is also observed in APCI. Betalactams are generally analysed in positive-ion or negative-ion LC-ESI-MS. 

Conventional positive-ion and negative-ion modes (PI and NI. respectively), the use of ammonium acetate and ammonium formate and the addition of 2% chloroacetonitrile in the liquid chromatographic eluent using filament-on thermospray LC-MS have been applied for the determination of selected herbicides. By using aoetonitrile-vater and 0.05 M anmonium acetate mixtures, the chlorotriazine herbicides shoved [M + (Cl CN) ] and... 

A method that uses high performance liquid chromatography/ mass spectrometry (HPLC/MS) for the analysis of chlorinated phenoxyacid herbicides is described. During method development different techniques were used to increase both the sensitivity and the specificity of thermospray HPLC/MS for chlorinated acid herbicides. These included the operation of the instrument in the negative chemical ionization (NCI) mode initiated by discharge and the use of a wire-repeller in the ion source for efficient extraction of positive ions. Single quadrupole repeller-induced and multiple quadrupole collision activated dissociation (CAD) experiments were also performed to increase the structural information of the mass spectra. 

Eight of the nine compounds are chlorinated phenoxyadds dalapon is a chlorinated aliphatic acid. The positive ion thermospray mass spectra of these pesticides are summarized in Table I. The base peak in all cases is the (M+NH4)+ ion for 2,4-DB the (M+H) ion is present No ions were detected for dalapon. Since the protonated molecule is present for 2,4-DB this compound has the highest apparent proton affinity among these herbicides. 

Since two ions per compound at most are generated in the positive ion mode, little structural information is obtained from these spectra. Consequently, three options to the single quadrupole positive ion thermospray mode were tested (1) NCI initiated by discharge (2) daughter ion CAD in the MS/MS mode of the (M+NH4)+ ions and (3) repeller-induced fragmentation in the positive ion single quadrupole mode. 

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