SPME vs. LLE: Optimization of Sample Preparation Techniques for Polyphenols of Grape and Wine
Presented by: Fatemeh Mousavi
A 96-thin-film SPME system was applied for simultaneous preparation of up to 96 samples for extraction of phenolic compounds from grape and wine. Polystyrene-divinylbenzene copolymer with a weak anion exchanger was used as extractive phase for the SPME system. The open-bed 96-format SPME system provided high throughput sample preparation of complex samples (in a total 210 min corresponding to <2.2 min per sample) without any need for further sample pretreatment. Phenomenon of ion suppression and ion enhancement can affect detection capability, precision, and accuracy of the method. The “sample dilution” method was used for evaluation of matrix effect in SPME and liquid-liquid extraction (LLE): the final extracts of both methods were prepared with different dilution factors (e.g., 2, 5, 10, 20, 50), and the normalized extrcated masses for each point were drawn versus the dilution factors. The data showed that LLE method provided in significant matrix effect (up to dilution factor of 20 in many cases). In contrast, SPME resulted in much more reliable results (no dilution or very low dilution was required). This can be explained due to more effective sample preparation and clean-up in SPME through selective extraction of compounds. Furthermore, SPME allows for determination of both free and total concentrations of compounds using a single sample by employing proper calibration strategies (matrix-free for unbound concentration and matrix-matched for total concentration). In this study, determination of free concentration of phenolic compounds in grape and wine samples provided us with important information regarding the bioavailable concentration of compounds in human body (important advantage in contrast with LLE). In addition, standard addition was used for determination of total concentration of phenolic compounds in grape and wine, and valuable insights regarding presence of several binding sites and adsorption mechanism in grape and wine samples were obtained.