Formation of Metal-Adducted Analyte Ions by Flame-Induced Atmospheric Pressure Chemical Ionization Mass Spectrometry

• Published in: Analytical chemistry (Washington) Vol. 88; no. 10; pp. 5159 - 5165
• Main Authors: Cheng, Sy-Chyi, Wang, Chin-Hsiung, Shiea, Jentaie
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17-05-2016
• Subjects: Analytical chemistry; Atmospheric pressure; Barometric pressure; Chemicals; Chlorides; Ethers; Inhalers; Ionization; Ions; Mass spectrometry; Metals; Needles; Stainless steel
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.6b00096

A flame-induced atmospheric pressure chemical ionization (FAPCI) source, consisting of a miniflame, nebulizer, and heated tube, was developed to ionize analytes. The ionization was performed by reacting analytes with a charged species generated in a flame. A stainless steel needle deposited with saturated alkali chloride solution was introduced into the mini oxyacetylene flame to generate alkali ions, which were reacted with analytes (M) generated in a heated nebulizer. The alkali-adducted 18-crown-6 ether ions, including (M + Li)+, (M + Na)+, (M + K)+, (M + Rb)+, and (M + Cs)+, were successfully detected on the FAPCI mass spectra when the corresponding alkali chloride solutions were separately introduced to the flame. When an alkali chloride mixture was introduced, all alkali-adducted analyte ions were simultaneously detected. Their intensity order was as follows: (M + Cs)+ > (M + Rb)+ > (M + K)+ > (M + Na)+ > (M + Li)+, and this trend agreed with the lattice energies of alkali chlorides. Besides alkali ions, other transition metal ions such as Ni+, Cu+, and Ag+ were generated in a flame for analyte ionization. Other than metal ions, the reactive species generated in the fossil fuel flame could also be used to ionize analytes, which formed protonated analyte ions (M + H)+ in positive ion mode and deprotonated analyte ions (M – H)− in negative ion mode.