Chlorine Isotope Analysis of Submicromole Organochlorine Samples by Sealed Tube Combustion and Thermal Ionization Mass Spectrometry

Abstract

Improved sensitivity in the analysis of stable chlorine isotopes of organochlorines (delta(37)Cl-OCl) has been established using sealed tube combustion in conjunction with thermal ionization mass spectrometry (TIMS). TIMS of chlorine isotopes was performed on <85 nmol of Cl with an achievable precision of <0.25 per thousand for pure inorganic chloride samples and 0.46 per thousand for chloride liberated from organochlorines (OCls). This makes possible significant reductions in the overall sample size requirement, as compared to the techniques of gas source stable isotope ratio mass spectrometry (SIRMS). Yields in excess of 99% were demonstrated in the dechlorination of <0.14 micromol 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and the overall yield, including purification of liberated chloride, was 86-97%. The accuracy of TIMS in the measurement of chlorine isotopes derived from OCls was confirmed by analysis of a DDT sample previously analyzed with SIRMS.(9) Using the described method for TIMS, the DDT sample gave a bulk chlorine isotope ratio of delta(37)Cl -4.42 +/- 0.46 per thousand (1sigma). The reported value from SIRMS analysis is -4.34 +/- 0.25 per thousand, indicating the conformity of the two methods.