Influence of the solvent on the gas chromatographic behaviour of urea herbicides

Degradation products of chlorsulfuron, chlortoluron, diuron, fluometuron, i soproturon, linuron, metabenzthiazuron, metobromuron, and monuron formed in the gas chromatographic injector have been used for identification of the respective herbicides. Mass spectra of the derived compounds were obtained with a quadrupole mass spectrometric detector working in scan mode (20-450 amu). The compounds generated often depended on the solvent used for phenyl urea herbicide injection (ethanol, methanol, dichloromethane, and acetonitr ile). When methanol and ethanol were used as solvents the major products fo rmed from phenylureas were carbamic acid esters. When acetonitrile or dichl oromethane were used the main derivatives were phenylisocyanates. Chlorsulf uron and metabenzthiazuron, however, generated a triazine plus a phenylsulf onamide and a benzothiazolamine, respectively, irrespective of the solvent used. Linuron and diuron behaved similarly and gave degradation products wi th the same mass spectra. The thermal reactions occurred instantaneously in the injector block and were promoted by the high temperature selected (300 degreesC). Determination of the compounds derived from urea herbicides, by use of a 30 m BP10 column and a selected ion registering (SIR) program based on two or three ions, can be used for sensitive detection of the presence of urea he rbicides in environmental extracts. With standards in methanol instrument d etection limits ranged from 0.1 pg for chlorsulfuron (detected as 2-chlorob enzensulfonamide) to 1 pg for monuron and metobromuron (both detected as th eir carbamic acid methyl esters). RSD were below 9% at the 5 ng L-1 level. The response was linearly dependent on quantity (r > 0.9986) in the 5 ng L- 1 to 25 mug L-1 range. Unequivocal identification of some phenylurea herbic ides was not always possible because some herbicides with similar structure s, for example diuron and linuron, gave the same derivative.