Strategies for single-drop microextraction optimisation and validation. Application to the detection of potential antimicrobial agents.

Convenient methods that are capable of determining potentially antimicrobial compounds in both vapour and liquid phases are required (inter alia) to facilitate the development of active packaging materials using natural substances. The suitability of single-drop microextraction (SDME) coupled with gas chromatography-mass spectrometry (GC-MS) for this purpose has been assessed by evaluating its ability to determine a range of analytes (mainly terpenes) in vapour samples and three liquid food simulants - distilled water, 10% (v/v) water/ethanol, and 3% (w/v) acetic acid - by headspace-SDME (HS-SDME) and direct immersion-SDME (DI-SDME), respectively. In this contribution, a screening strategy based on the Hildebrand solubility parameter has been used to build a solvent priority list. Solvents were then tested following the list, taking into account additional factors such as low volatility for HS-SDME or buoyancy and relative miscibility for DI-SDME. Other experimental parameters affecting the performance of SDME (such as drop volume, sampling time and temperature, drop position in the sample vial, sample vial size, stirring rate, filling rate and ionic strength of the sample) were investigated using a Plackett-Burman screening design. The method optimisation was completed by means of response surface modelling (RSM). The methods were validated by characterising relevant performance parameters including their robustness, linear range, accuracy (trueness and precision) and capability of detection as described by the International Organization for Standardization.