Improving the sensitivity in the SPME-GC analysis of free fatty acids from food and other biological samples

The aim of this study has been the evaluation of a new method to increase the sensitivity in the headspace - solid phase microextraction - gas chromatographic (HS-SPME-GC) analysis of free fatty acids (FFAs) found in foods and other biological samples. Among the different parameters playing a role to this purpose, the salting out effect has been taken into consideration, by evaluating an alternative to the classical salting out agent sodium chloride (SC). The idea arose from a study of Barrio et al.1, where the authors applied the salt mixture sodium di-hydrogen phosphate and ammonium sulfate (SDP/AS) to the extraction of pesticides by microextraction. Due to their high solubility in water and to their multivalent nature, we supposed that these salts could be a valid alternative to sodium chloride (SC), that is the classical salting out agent used in most of the SPME applications. Thus, in our study we investigated if the salt combination SDP/AS could improve the HS-SPME extraction of FFAs, as compared to the use of SC. The effect has been evaluated by using a standard mixture of FFAs (acetic, C2, propionic, C3, butyric, C4, pentanoic, C5, isopentanoic, iC5, hexanoic, C6, isohexanoic, iC6, octanoic, C8, and decanoic acid, C10) as well as by analyzing real samples naturally containing FFAs, as wine, cheese and rat feces. The salts mixture SDP/AS in the proper total amount and in the proper ratio, revealed to be highly efficient by improving the sensitivity obtained for all of the FFAs investigated. The experiments on the standards mixture of FFAs as well as on the real samples, confirmed the improved extraction efficiency given by the salts mixture, demonstrating that it can be used in the HS-SPME-GC analysis of FFAs and that is particularly useful when high sensitivity is needed. References: 1) Barrio, C.S.; Melgosa, E.R.; Asensio, J.S.; Bernal, J.G. Mikrochimica Acta 1996, 122, 267-277.