Positive ion chemical ionisation

Greaves and Unger [218] have used chemical ionisation mass spectrometry with positive ion chemical ionisation to qualitatively (full scan) and quantitatively (SRMS) determine tributyl tin, dibutyltin and mobutyltin in environmental waters. Detection... 

The positive ion chemical ionisation process using ammonia as reagent gas... 

J.E.P. Syka in Positive Ion Chemical Ionisation with an Ion Trap Mass Spectrometer, Finnegan MAT IDT Publication No.l9. 

The combination of both modes of operation, positive and negative offers complementary information. This is why most modern instruments offer the possibihty of recording what is known as a PPINICI spectrum, the acronym being derived from pulsed positive ion/ negative ion chemical ionisation. This method allows for the automated quasi-simultaneous recording of positive ion and negative ion spectra. 

Kallio, H. and Currie, G. (1993a) Analysis of low erucic acid turnip rapeseed oil (Brassica campesteris) by negative ion chemical ionisation tandem mass spectrometry. A method giving information on the fatty acid composition in positions sn-2 and sn- /3 of triacylglycerols. Lipids, 28, 207-15. 

The first step in most chemical reactions involves the breaking of a bond. In the reactions considered so far, both electrons of a pair are transferred from the bond to one of the fission products, which since it has an electron in excess of its requirements, becomes a negative ion. The other fission product is electron deficient and becomes a positive ion. The ionisation of water (Equation 22) is an... 

Bowadt, F.E. et al (1993) Combined positive and negative ion chemical ionisation for the analysis of PCB S, in ISth International Symposium on Capillary Chromatography, Riva del Garda, May 1993 (ed. P. Sandra), Huethig. 

Barcelo [13] characterised selected pesticides by negative ion chemical ionisation thermospray high performance liquid chromatography-mass spectrometry. Ions observed in the negative ion chemical ionisation spectra corresponded to mechanisms of anion attachment ([M + acetate], electron capture ([M] ) and dissociative electron capture ([M-R] ). Sensitivity was lower in the negative ion chemical ionisation mode than in the positive ion mode. 

Study of application of negative ion chemical ionisation MS, selected ion monitoring and pulsed positive ion/negative ion chemical ionisation MS Gas chromatography-mass spectrometry... 

Detection of M2D-C3-0-(E0)n-CH3 was possible by both positive ion mode atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) MS methods, with good response down to absolute injections of 0.1 ng. However, ionisation in the negative ion mode was negligible at all concentrations analysed, as the polyether-modified structure has no sites capable of adducting with anions, nor has it any moieties capable of cleavage to yield anionic species. 

In one study, however, atmospheric pressure chemical ionisation (APCI)-MS was applied for the simultaneous determination of LAS and octylphenol ethoxylates (OPEO) in surface waters after preconcentration by solid-phase extraction (SPE) on Cis cartridges [1]. In the chromatogram from a Ci-reversed phase (RP) column, peaks arising from both the anionic LAS and the non-ionic OPEO were detected after positive ionisation, while in negative ionisation mode, OPEO were discriminated and only the anionic surfactant was observed. Surprisingly, the relative sensitivity for detection of LAS was approximately five times higher in positive ion mode, which led the authors to the conclusion that this ionisation mode was desirable for quantitative work. 

Chemical ionisation results from the gas-phase collision between the analyte and species formed from the reagent gas introduced concomitantly in the ion source and bombarded by electrons. Methane, ammonium or isobutane are often used as reagent gases (Fig. 16.17). The reagent gas is introduced into the ion source at a pressure of a few hundred pascals, which reduces the mean free path and favours collision. Chemical ionisation produces positively and negatively charged species. 

Secondary electrons, i.e. those that have been ejected from atoms by incident radiation, will cause further ionisations or excitations until their energy is reduced to — kT, when they are said to be thermalised. They may then be captured by positive ions or neutral molecules. Since all ionising radiations then basically give rise to these secondary electrons, it is to be expected that their chemical effects will be essentially similar. 

Lacorte and Barcelo [36] have described a procedure for the determination of nanogram per litre levels of organophosphorus pesticides in ground waters based on automated online liquid-solid extraction followed by liquid chromatography. The detection used on the liquid chromatograph is an atmospheric pressure chemical ionisation mass spectrometer using negative and positive ion modes of operation. 

Figure 6. Reconstructed ion current LC/APCI/MS (positive ion) chromatogram of a mixture of 19 analytes (each 10 J.g/ml in water). l.MPA, 2. TDGO, 3. triethanolamine, 4. jV-methyldiethanolaminc, 5. EPA, 6. iV-ethyldietha-nolamine, 7. thiodiglycol sulfone, 8. 3-quinuclidinol, 9. EMPA, 10. TDG, 11. n-PrPA, 12. diisopropylaminoethanol, 13. EEPA, 14. r -PrMPA, 15. tert-BuPA, 16. w-BuPA, 17. cHexMPA, 18. Pin MPA, 19. benzilic acid. (Reprinted from Journal of Chromatography A, 759, R.M. Black and R.W. Read, Application of liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry, and tandem mass spectrometry, to the analysis and identification of degradation products of chemical warfare agents, pp. 79-92 (1997), with permission from Elsevier)...

R.W. Read and R.M. Black, Rapid screening procedures for the hydrolysis products of chemical warfare agents using positive and negative ion liquid chromatography-mass spectrometry with atmospheric pressure chemical ionisation, J. Chromatogr., A, 862, 169-177 (1999). 

Detection atmospheric pressure chemical ionisation (positive or negative mode), selected ion mode. 

Since the background ion current of the positive ion methane chemical ionisation mass spectrum in the region of 10-60 m/z was intense, no attempt was made to monitor the evolution of hydrogen chloride ( H Cl, m/z 36). Protonated molecular ions were observed for the major fragments with the exception of methylnaphthalene, methylanthracene, and ethylanthracene. The nominal structures for the fragments that result from the thermal degradation of the polyene are shown in Table 4.1. 

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