N-Acylated homoserine lactones (AHLs) are produced by Gram-negative bacteria as communication signals and are frequently studied as mediators of the "quorum sensing" response of bacterial communities. Several reports have recently been published on the identification of AHLs from different species and attempts have been made to study their role in natural habitats, for example the surface of plant roots in the rhizosphere. In this article, different analytical methods, including bacterial biosensors and chromatographic techniques, are reviewed. A concept for assignment of the structures of AHLs is also presented. The retention behaviour of derivatives of AHLs containing beta-keto or hydroxyl groups and/or double bonds has been evaluated in relation to the separation behaviour of AHLs with saturated and unsubstituted alkanoyl chains. Samples have also been analysed by high resolution mass spectrometry (Fourier-transform ion-cyclotron-resonance mass spectrometry, FTICR-MS), nano liquid chromatography-electrospray ionization ion trap mass spectrometry (nano-LC-MS) and by the aid of a biosensor. The results obtained from ultra performance liquid chromatography (UPLC), FTICR-MS, nano-LC-MS, and bioassays have been compared to attempt structural characterisation of AHL without chemical synthesis of analytical standards. The method was used to identify the major AHL compound produced by the rhizosphere bacterium Acidovorax sp. N35 as N-(3-hydroxydecanoyl)homoserine lactone.

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This paper demonstrates the analysis of levetiracetam, a new chiral antiepileptic drug, at ng/mL levels using an ultra-high-performance liquid chromatography (UHPLC)-photodiode absorbance (PDA) method. Three different sample preparation methods, liquid-liquid extraction with Extrelut, solid phase extraction (SPE) with Oasis HLB and Oasis MAX SPE cartridges, and protein precipitation with organic solvents were carried out. The last preparatory method is the simplest and provides the best recoveries: between 97.1% and 100.4% with RSD value below 5%. The column for separation is BEH C18 column (1.7 µm particle size and 100 × 2.1 mm i.d.) and acetonitrile-phosphate buffer (pH = 6.6; 0.01 M) (10/90 v/v) is the mobile phase. The results obtained are compared to analysis conducted by the HPLC method. The UHPLC method was validated in the range of 2-100 µg/mL levetiracetam concentration (R(2) = 0.9997). LOD and LOQ are 10 ng/mL and 33 ng/mL, respectively. The developed UHPLC method was applied to plasma samples of patient with epilepsy.

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