Thermospray Ionization Mass

K. Straub and K. Chan, Molecular weight determination of proteins from multiply charged ions using thermospray ionization mass spectrometry. Rapid Commun. Mass Spectrom., 4 (1990) 267. 

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. 

One of the reasons for lack offlterature was probably because environmental analysis depends heavily on gas chromatography/mass spectrometry, which is not suitable for most dyes because of their lack of volatility (254). However, significant progress is being made in analyzing nonvolatile dyes by newer mass spectral methods such as fast atom bombardment (EAB), desorption chemical ionization, thermospray ionization, etc. 

See footnote cto Table3 LC/PB/MS = hquid chromatography/particle beam mass spectrometry LC/APcl/ESl-MS/MS = liquid chromtography/atmospheric pressure chemical ionization/electrospray ionization tandem mass spectrometry LC/FTIR = Fourier transform infrared LC/TSP-MS/MS = liquid chromatography/thermospray tandem mass spectrometry LC/TSP-MS = liquid chromatography/thermospray mass spectrometry. 

Yinon et al. (228) used an HPLC interfaced with a triple-quadrupole mass spectrometer by means of a particle beam for the identification of several azo dyes. Characterization of the dyes was achieved by observing typical fragment ions formed by cleavage of the N-C and C-N bond on either side of the azo linkage and/or cleavage of the N=N double bond with the transfer of two hydrogen atoms to form an amine. Sensitivity was observed to be two to three orders of magnitude worse than with thermospray ionization. 

LD Betouski, JM Ballard. Identification of dyes by thermospray ionization and mass spectrome-try/mass spectromelogy. Anal Chem 56 2604 -2609, 1984. 

Fischer, J. and J. Michael (1995). Thermospray ionization liquid chromatography-mass spectrometry and chemical ionization gas chromatography-mass spectrometry of hexazione metabolites in soil and vegetation extracts. J. Chromatogr. A, 704(1) 131-139. 

The LC/MS analyses were performed with either thermospray ionization (TSI) or particle beam (PB) interfaces. These systems successfully analyzed the labile, polar, or higher mass compounds, whereas a complementary gas chromatography (GC)/MS system was used for volatile compounds. The LC/MS system proved to be widely applicable to a range of chemically diverse compounds. The TSI and PB systems were both successful for 80-90% of the compounds analyzed. Automated, open-access LC/MS analyses performed well because sample throughput was expected to reach 250,000 in 1995. This throughput corresponds to approximately 1000 samples per day. 

An ideal interface should not cause extra-column peak broadening. Historical interfaces include the moving belt and the thermospray. Common interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Several special interfaces include the particle beam—a pioneering technique that is still used because it is the only one that can provide electron ionization mass spectra. Others are continuous fiow fast atom bombardment (CF-FAB), atmospheric pressure photon ionization (APPI), and matrix-assisted laser desorption ionization (M ALDl). The two most common interfaces, ESI and APCI, were discovered in the late 1980s and involve an atmospheric pressure ionization (API) step. Both are soft ionization techniques that cause little or no fragmentation hence a fingerprint for qualitative identification is usually not apparent. 

This fact can be attributed to its lower number of substituents and consequently lower proton affinity in comparison with the other two triazines. In contrast, it has been reported that when filament-off or thermospray ionization is employed [M + H]+ is the base peak for different chloroatrazines (21,6) similarly as when DLI LC-MS was used (13). Such a difference in the relative abundance of the different adducts in the mass spectrum between filament-on and filament-off has been previously observed for other groups of pesticides (22,23). For ohlorotriazines a [M + 60]+-ion was the base peak using an eluent of methanol-water and ammonium... 

Thermospray LC/MS has been extensively used for the study of sulfonylurea herbicides (1-2). These compounds are thermally labile and can not be successfully analyzed by conventional GC/MS. Early applications of thermospray LC/MS included metabolite identification and product chemistry studies. We have recently evaluated the use of thermospray LC/MS for multi-sulfonylurea residue analysis in crops and have found the technique to meet the criteria for multiresidue methods. LC/MS offers both chromatographic separation and universal mass selectivity. Our study included optimization of the thermospray ionization and LC conditions to eliminate interferences and maximize sensitivity for trace level analysis. The target detection levels were SO ppb in crops. Selectivity of the LC/MS technique simplified sample extraction and minimized sample clean up, which saved time and optimized recovery. Average recovery for these compounds in crop was above 85%. 

Thermospray mass spectra often provide excellent molecular weight information, with some additional structural information being provided by fragment ions, via an ionization mechanism similar in "softness" to chemical ionization ( Cl ) Q) Spectra obtained by previous researchers from 22,23 dihydroavermectin Bia, a macrolide similar in structure to the nemadectins, demonstrated that chemical ionization mass spectrometry (A) and thermospray LC/MS (5.) provided excellent results. We anticipated, therefore, that the nemadectins would also be amenable to thermospray LC/MS analysis. 

Thermospray ionization has also been used with quadrupole mass spectrometry to investigate the novel anticonvulsant topiramate in rat brain [16]. Topi-ramate crosses the blood—brain barrier and the concentration of the drug remains in the micromolar range for more than 6 hr. Samples were collected every 15 min over this time period, and the authors planned to analyze the dialysate without further sample cleanup. Distilled water was used as the perfusion medium to minimize the effect of dialysis salts on the mass spectrometer. I lowcver, it is important to note that microdialysis is best performed with matching ionic... 

In recent years, several techniques have been developed for mass spectrometry, whereby samples are ionized and analysed from a condensed phase, without prior volatilization. These desorption techniques have permitted the extension of mass spectrometric analyses to sulfate and glutathione conjugates, as well as to underivatized and labile glucuronic acid conjugates. Primary among these techniques are field desorption 6, plasma desorption (7), laser desorption (8), fast atom bombardment (or secondary ion mass spectrometry with a liquid sample matrix) ( ) and thermospray ionization ( O). The latter can also serve to couple high pressure liquid chromatography and mass spectrometry for analysis of involatile and thermally labile samples. 

HA, heterocyclic amine AA, aromatic amine PA, polyamine Al, aliphatic amine N, nitrosamine BCD, electrochemical UV, ultraviolet FL, fluorescence TSI, thermospray ionization ESI, electrospray ionization MS, MS-tandem mass spectrometry SIM, selected ion monitoring A, air H, water W, waste. 

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