Intramolecular carbon and nitrogen isotope analysis by quantitative dry fragmentation of the phenylurea herbicide isoproturon in a combined injector/capillary reactor prior to GC separation.
Potentially, compound-specific isotope analysis may provide unique information on source and fate of pesticides in natural systems. Yet for isotope analysis, LC-based methods that are based on the use of organic solvents often cannot be used and GC-based analysis is frequently not possible due to thermolability of the analyte. A typical example of a compound with such properties is isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea), belonging to the worldwide extensively used phenylurea herbicides. To make isoproturon accessible to carbon and nitrogen isotope analysis, we developed a GC-based method during which isoproturon was quantitatively fragmented to dimethylamine and 4-isopropylphenylisocyanate. Fragmentation occurred only partially in the injector but was mainly achieved on a heated capillary column. The fragments were then chromatographically separated and individually measured by isotope ratio mass spectrometry. The reliability of the method was tested in hydrolysis experiments with three isotopically different batches of isoproturon. For all three products, the same isotope fractionation factors were observed during conversion and the difference in isotope composition between the batches was preserved. This study demonstrates that fragmentation of phenylurea herbicides does not only make them accessible to isotope analysis but even enables determination of intramolecular isotope fractionation.
Penning
Holger
H
Institute of Groundwater Ecology, GSF-Research Center for Environment and Health, Ingolstädter Landstrasse 1, 85764 Neuherberg, Germany. holger.penning@gsf.de
Elsner
Martin
M
D002247:Carbon Isotopes / Q000032:analysis; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006540:Herbicides / Q000737:chemistry*; D006868:Hydrolysis; D008752:Methylene Chloride / Q000737:chemistry; D015394:Molecular Structure; D009587:Nitrogen Isotopes / Q000032:analysis; D010671:Phenylurea Compounds / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
D002247:Carbon Isotopes; D006540:Herbicides; D009587:Nitrogen Isotopes; D010671:Phenylurea Compounds; D012997:Solvents; D008752:Methylene Chloride; C028904:isoproturon