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Accurate Isotope Data is Essential for Determining Elemental Compositions

Introduction

Elemental compositions are commonly determined from high-resolution mass spectra and accurate mass measurements. Given a measured mass (m/z) and a range of elements that can be present, software calculates the exact mass for each combination of elements and reports all elemental combinations that match the measured mass within a specified error tolerance. Improving the mass accuracy reduces the number of elemental compositions, but mass accuracy alone may not be sufficient to determine the correct elemental composition for an unknown sample.

JEOL AccuTOF™ mass spectrometers (the AccuTOF™-DART®, the AccuTOF™-GCX and the AccuTOF™-GCX Plus) are capable of accurate isotope measurements that can be used to determine elemental compositions from high-resolution mass spectra. Matching the measured abundances and exact masses for isotope peaks can be more effective than mass accuracy alone.

Experimental

A JEOL AccuTOF™-DART® mass spectrometer was used to acquire positive-ion mass spectra at a resolving power of >10,000 (FWHM). The DART was operated in positive-ion mode with helium gas and a gas heater temperature of 350°C. Chlorpromazine was analyzed by dipping a melting point tube into a dilute solution of chlorpromazine in dichloromethane and dangling the tip of the tube in the DART gas stream. Jeffamine® M-600 (Huntsman) copolymer was measured in the same data file as an external calibrant for exact mass measurements. Mass Mountaineer™ software was used for elemental composition determinations from accurate mass measurements and isotope matching.

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