title: Isomeric differentiation of polycyclic aromatic hydrocarbons using silver nitrate reactive desorption electrospray ionization mass spectrometry.
abstract: BACKGROUND
  Polycyclic aromatic hydrocarbons (PAHs) are nonpolar and difficult to detect by desorption electrospray ionization. We present a new detection method based on cationization with silver ions, which has the added advantage of being able to differentiate PAHs with the same mass but different structure.
  
  
  METHODS
  9,10-Diphenylanthracene and triptycene, in addition to four different groups of PAH isomers: (1) anthracene and phenanthrene, (2) pyrene and fluoranthene, (3) benz[a]anthracene, benz[b]anthracene (tetracene), and chrysene (4) benzo[a]pyrene and benzo[k]fluoranthene, were deposited on a paper surface and bombarded with methanol droplets containing silver nitrate. The resulting microdroplets entered a quadruple mass spectrometer for mass analysis.
  
  
  RESULTS
  The mass spectrum shows [PAH](+), [Ag + OH + PAH](+), and [Ag(PAH)(n)](+) (n = 1, 2) (and [PAH + O(2)](+) in the case of benz[b]anthracene) ions. PAHs having a bay structure, such as phenanthrene, showed a different tendency to interact with silver ions from those PAHs having a linear arrangement of the fused benzene rings, such as anthracene. The ratios of the [PAH](+) peak intensity to that of [Ag-PAH](+), [Ag + OH + PAH](+), [Ag(PAH)(2)](+), and [PAH + O(2)](+) were used to differentiate the PAH isomers sharing the same molecular formula with different structures. For isomeric mixtures the [PAH](+) to [Ag + OH + PAH](+) ratio was found to be the most useful parameter. The uncertainty in the mole fraction of an isomeric mixture was ±0.09, ±0.13, ±0.25, and ±0.1 for phenanthrene-anthracene, fluoranthene-pyrene, benz[a]anthracene-chrysene, and benzo[a]pyrene-benzo[k]fluoranthene, respectively.
  
  
  CONCLUSIONS
  A simple method has been developed for the detection of PAHs in desorption electrospray ionization mass spectrometry based on Ag(I) cationization. The method showed a capability to differentiate PAHs isomers (having the same molecular mass) in isomeric mixture with an uncertainty in the mole fraction of about ±0.1. At high inlet temperature and voltage, this method showed better sensitivity but less ability to differentiate between isomeric species.
authors: Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA.
authors: Mohammad
authors: M
authors: Eftekhari
authors: Ali I
authors: AI
authors: Ismail
authors: Richard N
authors: RN
authors: Zare