Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Chemical ionization

Chemical ionization (CI) is an ionization technique used in mass spectrometry.Munson, M.S.B.; Field, F.H. J. Am. Chem. Soc. 1966, 88, 2621-2630. Chemical Ionization Mass Spectrometry. I. General Introduction.Fales HM, Milne GW, Pisano JJ, Brewer HB, Blum MS, MacConnell JG, Brand J, Law N Biological applications of electron ionization and chemical ionization mass spectrometry Recent Prog. Horm. Res. 28 591–626 1972 4569234 Dougherty RC Negative chemical ionization mass spectrometry: applications in environmental analytical chemistry Biomed. Mass Spectrom. 8 7 283–92 1981 7025931 10.1002/bms.1200080702 Chemical ionization is a lower energy process than electron ionization. The lower energy yields less fragmentation, and usually a simpler spectrum. A typical CI spectra has an easily identifiable molecular ion.de Hoffmann Edmond Vincent Stroobant Mass Spectrometry: Principles and Applications John Wiley & Sons, Ltd. Toronto 2003 Second 0471485667 14 Mechanism In a CI experiment, ions are produced through the collision of the analyte with ions of a reagent gas that are present in the ion source. Some common reagent gases include: methane, ammonia, and isobutane. Inside the ion source, the reagent gas is present in large excess compared to the analyte. Electrons entering the source will preferentially ionize the reagent gas. The resultant collisions with other reagent gas molecules will create an ionization plasma. Positive and negative ions of the analyte are formed by reactions with this plasma. Primary Ion Formation Secondary Reagent Ions Product Ion Formation (protonation) ( abstraction) (adduct formation) (charge exchange) Self chemical ionization occurs when the reagent ion is an ionized form of the analyte. 10.1021/ac00226a011 Chemical ionization in Fourier transform mass spectrometry 1981 Sahba. Ghaderi; P. S. Kulkarni; Edward B. Ledford; Charles L. Wilkins; Michael L. Gross Analytical Chemistry 53 428 Variations Negative chemical ionization (NCI) Chemical ionization for gas phase analysis is either positive or negative. Almost all neutral analytes can form positive ions through the reactions described above. In order to see a response by negative chemical ionization, the analyte must be capable of producing a negative ion (stabilize a negative charge) for example by electron capture ionization. Because not all analytes can do this, using NCI provides a certain degree of selectivity that is not available with other, more universal ionization techniques (EI, PCI). NCI can be used for the analysis of compounds containing acidic groups or electronegative elements (especially halogens).de Hoffmann Edmond Vincent Stroobant Mass Spectrometry: Principles and Applications John Wiley & Sons, Ltd. Toronto 2003 Second 0471485667 23 Because of the high electronegativity of halogen atoms, NCI is a common choice for their analysis. This includes many groups of compounds, such as PCBsKontsas Helena Kaija Pekari 2003-07-05 Determination of polychlorinated biphenyls in serum using gas chromatography–mass spectrometry with negative chemical ionization for exposure estimation Journal of Chromatography B Elsevier, Ltd. 791 1-2 117–125 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6X0P-48B5FR8-D&_user=1069125&_coverDate=07%2F05%2F2003&_alid=759548054&_rdoc=3&_fmt=high&_orig=search&_cdi=7220&_sort=d&_docanchor=&view=c&_ct=8&_acct=C000051259&_version=1&_urlVersion=0&_userid=1069125&md5=a1aa7b8733e3fe4a2e0cb1bc49509fc0 2008-06-26 10.1016/S1570-0232(03)00216-2, pesticidesRivera-Rodríguez Laura B. Ricardo Rodríguez-Estrella, James Jackson Ellington and John J. Evans 2007-07 Quantification of low levels of organochlorine pesticidesnext term using small volumes (≤100 μl) of plasma of wild birds through gas chromatography negative chemical ionization mass spectrometry Environmental Pollution Elsevier, Ltd. 148 2 654–662 http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VB5-4MVN09G-8&_user=1069125&_coverDate=07%2F31%2F2007&_alid=759547122&_rdoc=2&_fmt=high&_orig=search&_cdi=5917&_sort=d&_docanchor=&view=c&_ct=16&_acct=C000051259&_version=1&_urlVersion=0&_userid=1069125&md5=d3b5083a60609546bfb2a7f3e5bdb87e 2008-06-26 10.1016/j.envpol.2006.11.018 17240024, and fire retardants.Lacorte Sylvia Míriam Guillamon Validation of a pressurized solvent extraction and GC–NCI–MSnext term method for the low level determination of 40 polybrominated diphenyl ethers in mothers’ milk Chemosphere Elsevier, Ltd. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V74-4SV6PC5-3&_user=1069125&_coverDate=06%2F25%2F2008&_alid=759545286&_rdoc=1&_fmt=high&_orig=search&_cdi=5832&_sort=d&_docanchor=&view=c&_ct=168&_acct=C000051259&_version=1&_urlVersion=0&_userid=1069125&md5=604968b27975bf81631130e76028b913 2008-06-26 Most of these compounds are environmental contaminants, thus much of the NCI analysis that takes place is done under the auspices of environmental analysis. Atmospheric pressure chemical ionization (APCI) Chemical ionization in an atmospheric pressure electric discharge is called atmospheric pressure chemical ionization. The analyte is a gas or liquid spray and ionization is accomplished using an atmospheric pressure corona discharge. This ionization method is often coupled with high performance liquid chromatography where the mobile phase containing eluting analyte sprayed with high flow rates of nitrogen and the aerosol spray is subjected to a corona discharge to create ions. References