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ANALYTICAL CURRENTS
Separating stereoisomers of chemical warfare agents Synthesis of the organophosphorous nerve agents sarin, tabun, soman, and cyclohexylmethylphosphonofluoridate (GF) produces a mixture of stereoisomers: two for tabun, sarin, and GF, and four for soman. Because the toxicity and acetylcholinesterase inhibition rates of the isomers are quite different, toxicological studies and development of antidotal therapies are greatly enhanced by the ability to distinguish between the stereoisomers. J. Richard Smith and John J. Schlager of the U.S. Army Medical Research Institute of Chemical Defense have used a gas chromatograph coupled with an atomic emission detector to test five commercially available derivatized cyclo-
ENDOR studies of iron in zeolites The incorporation of transition metals into the framework of aluminosilicate and aluminophosphate molecular sieves could potentially lead to new catalysts. Iron is known to be an impurity in many natural and synthetic zeolites in tetrahedral framework sites, as extra-framework cations or as an interstitial phase of small particles either within the zeolite pores or on the zeolite's external surface. D. Goldfarb of the Weizmann Institute of Science (Israel) and co-workers at Exxon and Leiden University (The Netherlands) have used highfrequency W-band (95 GHz) electronnuclear double resonance (ENDOR) spectroscopy to investigate the structure of several 57Fe-containing zeolites including Fe-sodalite Fe-L Fe-mazzite and FeMFI They determined that in contrast to Xband 57Fe ENDOR signals the W-band signals are free from second- and thirdorder contributions of the hvoerfine and zero-field splitting interactions and are thus sienificantly simpler to assign and interprpt Thev also found that the hvnerfine rouplinp constants of all four 7eolites
dextrin stationary phases for their ability to resolve the nerve agent stereoisomers. Three different fcyclodextrin phases (2,6-di-Opentyl-3-O-trifluoroacetyl, 2,6-di-O-pentyl-3-O-butyryl, and 2,6-di-0-pentyl-3-0Separation of soman enantiomers on a 2,6-di-0-pentyl-3propionyl) and two O-butyryl y-cyclodextrin stationary phase at65 °C isothermal. P-cyclodextrin (Adapted with permission of Huthig.) phases (2,6,-di-Opentyl-3-hydroxy and permethyl-O(S)-2-hydroxypropyl) were examined. Of were resolved to varying degrees on all the columns tested, only 2,6-di-0-pentyl-3-0- four stationary phases, but only the butrifluoroacetyl ycyclodextrin and 2,6-di-Otyryl y-cyclodextrin phase could sepapentyl-3-CMjutyryl •\K;yclodextrin were able rate isomers of all four of the nerve to successfully resolve all four soman iso~ agents. (/. High Resolut. Chromatogr. mers Enantiomers of tabun sarin andGF 1996,19,151-54)
are similar, which indicates that these values are typical for 57Fe(III) in framework sites of zeolites. For the sodalite, ENDOR signals of 23Na were also observed, and analysis of the 23Na powder patterns suggests a framework Fe(III) interacting with Na+ in the center of the six-member ring. (/. Am. Chem. Soc. 1196,118,4665-71)
Pulsed ENDOR spectra of57Fe-sodalite in the region of the 57Fe (Ms = -5/2) peak.
End-group determination by MALDI-FT-ICRMS Identification of end-group functionality can provide insight into the properties of synthetic polymers. Because the mass of the polymer is much larger than the mass of its end group, extremely high mass resolution, typically higher than that of time-of-flight instruments, is required for end-group determination. J. J. Boon and co-workers at FOM-Institute for Atomic and Molecular Physics (The Netherlands) have determined the end-group composition of polyethylene glycol by coupling ma~ trix-assisted laser desorption ionization (IVIALDI) to a 7-T external ion source Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. When the measured masses are analyzed, a linear regression of molecular weights as a function of degree of polymerization yields the mass of the repeating unit (the slope) and the sum of the residual mass of the end group plus the mass of the cation (y-intercept). Because the monomer mass uncertainty progressively adds to the uncertainty in the regres-
Analytical Chemistry News & Features, July 1, 1996 3 9 9 A
