Abstract:

【Objective】Resins from Liquidambar formosana Hance, known as Chinese sweet gum, is an important Chinese medicinal material with numerous beneficial effects including hemostasis and muscle, detoxification and pain relief. It is an oil-containing resin secreted by Liquidambar trees after trauma, and has numerous biological actions including anti-cancer, anti-inflammatory and analgesic effects. However, it is seldom processed and utilized in China, and, at present, is mainly exported. In order to improve the rationalization of the utilization and quality appraisal of Liquidambar resin, the composition and mass fraction of volatile components of resins from five areas were analyzed and compared. The results provide data to support a high-value utilization of Liquidambar resin.【Method】 Traditionally, volatile component extraction methods have mostly involved steam distillation. However, this usually consumes large amounts of raw materials, takes a long time, requires complex operations, and brings about decomposition of components due to the high temperature involved. Solid phase microextraction (SPME) is an advanced sample pretreatment technology that uses coated quartz fibers to extract volatile components, and release adsorbed volatile components for an analysis after heating. The advantages of SPME include simplicity, convenience, lower cost, ease of automation and high sensitivity. Moreover, it does not require the use of organic solvents during the extraction process, consequently it is an eco-friendly analysis method. In addition, it can be directly used with gas chromatography-mass spectrometry (GC-MS). In this study, SPME/GC-MS was employed to analyze Liquidambar resin samples from five different areas: Guilin Guangxi (GG), Baise Guangxi (GB), Longlin Guangxi (GL), Jiujiang Jiangxi (JJ) and Shunchang Fujian (FS). The SPME technique was used to extract volatile components from the resin samples and GC-MS was used for a component separation and identification. For extraction of components, a resin sample was placed in an Erlenmeyer flask which was sealed with plastic wrap. The extraction head was then inserted into the flask and positioned 5 cm away from the surface of the resin sample. Extraction was carried out for 40 min, followed by desorption at 250 ℃ for 3 min in preparation for the GC-MS analysis. The GC conditions were set as: DB-5MS capillary column (30 m × 0.25 mm× 0.25 μm); column flow rate: 1.00 mL/min, carrier gas mode: constant flow, sampling mode: split flow injection (split ratio 50:1), carrier gas: He (99.999%), inlet temperature: 250 ℃, and column initial temperature: 40 ℃. The temperature was programmed to increase to 100 ℃ at 5 ℃/min, and to 250 ℃ at 10 ℃/min. The peak area normalization method was employed to calculate the mass fraction of each component. The MS conditions were set as: EI ion source: electron energy 70 eV, ion source temperature: 250 ℃; mass spectrometer transmission line temperature: 250 ℃, and scanning range 45-450 amu. The solvent delay time was 0.5 min. The operating system was the Xcalibur software and the probable structures of the components, and the other related information was obtained with reference to the National Institute of Standards and Technology (NIST) of the United States database.【Result】Through SPME/GC-MS, a total of 64 probable compounds were identified from the volatile resin components, and 44, 41, 44, 37 and 32 of these compounds were identified in the volatile components extracted from the GG, GB, GL, JJ, and FS samples, respectively. The volatile components mainly included olefins, aldehydes, ketones, alcohols, ethers and alkanes. Among these, the olefin content was the highest (76.69%-92.07%). Terpenoids including β-caryophyllene, α-pinene, β-pinene, D-limonene and camphene were the main olefin components. The highest terpenoid content was 91.96% (GG) and the lowest was 66.26% (JJ). The order of terpenoid mass fractions in resins from the five areas was GG > GL > FS > GB > JJ. β-caryophyllene was the main terpenoid component and contributed 23.45% and 25.39% of the volatile components in the resins from GG and GB, respectively, but only 1.52% in the resin from JJ. The mass fractions of α-pinene in resins from GL, JJ and FS were 18.32%, 23.12% and 20.96%, respectively, but only 10.48% in volatile components of resin from GB. The content of β-pinene in volatile components of resins from GL and JJ was high (15.60% and 15.45%, respectively) but in resin from GB was low at only 10.27%. The mass fractions of D-limonene in resins from JJ and FS were higher (12.69% and 10.21%, respectively) than in resins from the other three areas which were less than 10%. The mass fractions of camphorene in volatile components of resins from FS and JJ were 11.40% and 8.18%, respectively, but only 3.35% in resin from GB. Thus it is evident that the composition and mass fractions of volatile components in resins from the five areas were significantly different.【Conclusion】The composition and mass fractions of volatile components of Liquidamber resins were analyzed by SPME/GC-MS. The SPME/GC-MS approach can be used effectively to identify the volatile components and some of the trace substances in the volatile components of Liquidambar resin from different areas. There were significant differences in the composition and mass fractions of volatile components of Liquidambar resin from the different areas, which may provide data to support the high-value utilization of this medicinal resource. For example, to obtain α-pinene, resins from FS, JJ and GL could be used as a raw material. To isolate β-pinene, resins from GL, JJ and FD would be suitable choices. If β-caryophyllene was the target, the Guangxi Liquidambar resin could be used as a raw material. This study showed that using SPME/GC-MS technology has advantages including lower dosage, less damage to samples, simple and rapid operation, high detection sensitivity, and high reliability, and that it is suitable for the quality evaluation and origin identification of Liquidambar resin. Using of this technology could be extended to the analysis of volatile components of the other substances including other resins, essential oils, flowers, and even tree barks.

Key words: Liquidambar resin, solid phase microextraction(SPME), gas chromatography-mass spectromentry(GC-MS), component analysis