Fragmentation Pathways in Electron Impact Mass Spectra of Methoxyhalobiphenyls Martin Th. M. Tulp zyxwvutsrq Laboratory of Environmental Chemistry, University of Amsterdam, Nieuwe Achtergracht 166, Amsterdam, The Netherlands Stephen H. Safe and Robert K. Boyd? Guelph-Waterloo Centre for Graduate Work in Chemistry (Guelph Campus), Guelph, Ontario, Canada N l G 2Wl The electron impact mass spectra of various methoxyhalobiphenylshave been reinvestigated. Previous findings, concerning the effect of the methoxy group upon the main fragmentation routes, have been confirmed and extended. in addition, studies of unimolecular and collision induced fragmentations of ions, using linked scan techniques, have been made. Such an approach permits the identification of substances with a minimal chromatographicseparation prior to mass spectrometry. It has also led to some clarification of the fragmentation pathways leading to the observed cracking patterns. INTRODUCTION The main metabolic products of chlorobiphenyls and bromobiphenyls in animals, plants and microorganisms are hydroxylated species.',' The mass spectra of the isomeric hydroxy derivatives of chlorobiphenyls are essentially identicaL3 More recently, it has been sh~wn~,~ that the methyl ethers of various fluoro- biphenylols, chlorobiphenylols and bromobiphenylols give characteristic cracking patterns under electron impact (EI). The position of the methoxy group relative to the biphenyl bond zyxwvutsrqp (ortho, meta or zyxwvutsr paru, i.e. 2-OCH3, 3-0CH3 or 4-OcH3 respectively) could be assigned unambigu~usly.~~~ The present work represents an attempt to extend the earlier mass spectrometric investigation^^-^ by exploit- ing techniques to obtain collisionally activated (CA) and metastable ion (MI) daughter ion spectra of mass selec- ted parent ions. The usefulness of such techniques has been well documented,6 more recently with respect to analysis of complex mixtures without preseparation by chromatographic It was hoped that such studies of methyl ethers of hydroxylated halogenated biphenyls, besides offering an ancillary analytical approach, would add to the understanding of the frag- mentation mechanisms which have been proposed for the observed regularitie~.~~~ zyxwvut EXXRIMENTAL Mass spectrometry All experiments were conducted using a VG Organic 7070F double focusing mass spectrometer. This instrument is equipped with a temperature-controlled Hall-effect probe and associated circuitry, which pro- t Author to whom proofs and inquiries should be directed. vide an electrical signal proportional to either magnetic field strength zyxw (B) or to its square (B'). The voltage providing the electric field in the electric sector could be slaved to the Hall probe output, thus permitting B/E linked scans?.'' of daughter ion spectra of mass selected parent ions, or else B2/E linked scans'" of precursor ion spectra of preselected fragment ions. A closeable p-slit permits optimization of the compromise between sensi- tivity and kinetic energy resolution. A collision cell, with a differential pumping ratio of approximately 100: 1, is located in the 1st field free region (FFR), immediately following the entrance slit of the electric sector. The ion accelerating voltage was 4 kV. All experiments were conducted using an ion source temperature of 200T, and unless stated otherwise, a nominal electron energy of 70 eV. Samples were intro- duced to the batch inlet system (at 200 'C) in solution in hexane. EI spectra were obtained at a scan speed of 3 s per mass decade. The MI and CA spectra, being less sensitive than EI spectra by factors of 10'--10 zy , were obtained at much slower scan speeds. Helium was used as collision gas in the CA experiments, at a pressure sufficient to reduce the intensity of the mass selected parent ion (B/E) or fragment ion (B2/E) to 30'/0 of its intensity in the absence of collision gas. Synthesis Compounds 1, 2 and 3 (X=F, Cl, Br, I) were synthesized by reacting an aniline with amyl nitrite in the presence of an appropriate aromatic reactant." In all cases a molar ratio of 1 :2: 10 for ani1ine:amyl nitrite : aromatic radical scavenger, was used. After slow addition (approximately 1 h) of the amyl nitrite, the mixture was heated slowly to 100'C and kept at that temperature for 2 h. The resulting compounds were purified by thin-layer chromatography (silica gel 60 F2S4, Merck, Germany, layer thickness 0.25 nm, hexane solvent). Compounds 1 were prepared from o-anisidine @ Heyden & Son Ltd, 1980 CCC-0306-042X/80/0007-0109$03.00 EIOMEDICAL MASS SPECTROMETRY, VOL, 7, NO. 3, 1980 zyx 109