On-line RPLC-GC analysis of terpenes using polydimethylsiloxane as a packing material

The effectiveness of absorbent polymers as packing materials alternative to adsorbents in the interface of the on-line coupling of RPLC to GC via PTV for the analysis of terpenes in orange juice was evaluated. To that aim, a comparative study of an absorbent (polydimethylsiloxane, PDMS), and an adsorbent (Tenax TA) was carried out. As a result, satisfactory repeatability was achieved from both packing materials obtaining relative standard deviation values lower than 10% in most cases. Regarding sensitivity, higher recoveries and far lower detection limits were however attained by using PDMS as the packing material inside the PTV injector. Specifically for PDMS the recoveries varied from 52% to 63% whereas in the case of Tenax TA values ranging from 10% to 22% were obtained. Detection limits varied from 1.5 to 1.9 ppb for PDMS and from 30 to 1900 ppb with Tenax TA. In addition to the sensitivity enhancement, PDMS proved to be more effective in the elimination of the solvent coming from the RPLC-pre-separation. Besides, PDMS is more thermally stable and, as a consequence, it results in lesser degradation products.