title: Gravitational sampling electrospray ionization mass spectrometry for real-time reaction monitoring.
abstract: BACKGROUND
  The elucidation of chemical reaction mechanisms has attracted tremendous interest in recent years. Here, gravitational sampling electrospray ionization mass spectrometry (GS-ESI-MS) is used to explore a simple method for the real-time monitoring of chemical and biochemical reactions.
  
  
  METHODS
  A sample solution in a stainless steel sample well is directly delivered through a fused-silica capillary due to the forces of gravity, capillary action, and electroosmotic flow (EOF). Analyte ions are continuously generated via electrospray ionization from the capillary tip when a high voltage is applied on the sample well.
  
  
  RESULTS
  Liquid solutions (<5 μL) of small organic compounds (e.g., crystal violet) and large biomolecules (e.g., reserpine, angiotensin II, and insulin) were directly analyzed via GS-ESI-MS. In addition, the technique was successfully applied to continuously monitor chemical [e.g. chelation of ethylenediaminetetraacetic acid (EDTA) with copper(II), and addition-elimination of aminophenol and acetic anhydride] and biochemical (e.g., unfolding of cytochrome c) reactions in real time, where chelation complexes, reaction intermediates, and protein conformation changes were observed.
  
  
  CONCLUSIONS
  GS-ESI-MS is a very simple modification of the ESI technique that does not require sample delivery pumps or nebulizer gases. It is particularly suitable for the analysis of liquid samples and the real-time monitoring of inorganic/organic chemical or biochemical reactions.
authors.affiliation: Department of Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan.
authors.forename: Fu-Jen
authors.initials: FJ
authors.lastname: Hsu
authors.forename: Te-Lin
authors.initials: TL
authors.lastname: Liu
authors.forename: Amzad Hussain
authors.initials: AH
authors.lastname: Laskar
authors.forename: Jentaie
authors.initials: J
authors.lastname: Shiea
authors.forename: Min-Zong
authors.initials: MZ
authors.lastname: Huang
mesh_terms: D006112:Gravitation; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation / Q000379:methods*
chemical_list: D007477:Ions; D009930:Organic Chemicals