Mass spectrometric and gas and high-performance liquid chromatographic behaviour of an impurity in 2,5-hexanedione

The analysis of 2,5-hexanedione, a metabolic compound of several industrial solvents, is normally carried out using gas chromatographic (GC) or GC-mass spectrometric (MS) techniques. This work, with the aim of verifying the possibility of determining the diketone by means of a high-performance liquid chromatographic (HPLC) method with UV detection, illustrates the importance of the choice of a 2,5-hexanedione standard for the determination of the diketone response factor. In some commercial diketone samples the presence of an impurity, which may interfere with the analysis of the target analyte, was ascertained. This impurity showed GC and HPLC behaviour similar to that of 2,5-hexanedione, but gave a very different UV response. This impurity was identified as 3-methylcyclopent-2-enone by means of MS, GC-MS, HPLC-photodiode-array detection, IR and UV spectrometry. The structure was confirmed by comparing the chromatographic, mass and ultraviolet data of the unknown compound with those of a synthesized reference sample. The well known difficulty in determining 2,5-hexanedione by HPLC with UV detection was reconfirmed owing to its low molar absorptivity.