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A new approach to determine method detection limits for compound‐specific isotope analysis of volatile organic compounds
Author(s) -
Jochmann Maik A.,
Blessing Michaela,
Haderlein Stefan B.,
Schmidt Torsten C.
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2784
Subject(s) - chemistry , btex , detection limit , ethylbenzene , volatile organic compound , bromoform , toluene , gas chromatography , chromatography , isotope analysis , benzene , isotope ratio mass spectrometry , gas chromatography–mass spectrometry , dichloromethane , chloroform , environmental chemistry , mass spectrometry , analytical chemistry (journal) , organic chemistry , ecology , solvent , biology
Compound‐specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on‐line CSIA with the lowest reported method detection limits (MDLs in the low µg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para ‐xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3‐trimethylbenzene, 1,2,4‐trimethylbenzene, 1,3,5‐trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis ‐1,2‐dichloroethene, trans ‐1,2‐dichloroethene, carbon tetrachloride, chloroform, 1,2‐dichloroethane, trichloroethene, tetrachlorethene, 1,2‐dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on δ 13 C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the δ 13 C mean values. The last concentration for which the δ 13 C value was within this iterative interval and for which the standard deviation was lower than ±0.5‰ for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 µg/L are the lowest values reported so far for continuous‐flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 µg/L. The environmental applicability of the P&T‐GC/IRMS method in the low‐µg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs. Copyright © 2006 John Wiley & Sons, Ltd.