Synthesis of deuterium-labelled fluorobenzoic acids to be used as internal standards in isotope dilution mass spectrometry.

A method for the deuterium labelling of fluorobenzoic acids (FBAs) via acidic H/D exchange of the aromatic hydrogen atoms in concentrated D2SO4 is described. The synthesis is shown to be easy, fast, low-priced and without the use of catalysts or further purification. The use of at least double-deuterated FBAs as internal standards in organic isotope dilution mass spectrometry allows the determination of FBAs in complex matrices with highest possible accuracy in combination with a simplified analytical evaluation.