Chemical analysis of floral odors via MicroSPE

Volatile collection - Floral scent is collected using dynamic headspace methods. A single, newly opened flower is enclosed within a polyethylene oven bag (Toppits®) and the emitted volatiles are trapped in an adsorbent tube through the use of a membrane pump (ASF Thomas, Inc.). The flow rate is adjusted to 200ml/min using a power supply and a flow meter. Samples are collected for 2 min during the time the material is emitting most of its volatiles.

ChromatoProbe quartz microvials of Varian Inc. (length: 15mm; inner diameter: 2mm) were cut at the closed end, filled with a mixture (1:1) of 3mg Tenax-TA (mesh 60-80) and Carbotrap (mesh 20-40), and used as adsorbent tubes. The adsorbents are fixed in the tubes using glass wool. Simultaneous collections of the surrounding air are used to distinguish between floral compounds and ambient contaminants.

polyethylene oven bag, adsorbent tube, membrane pump, flow meter, power supply	membrane pump ASF Thomas	adsorbent tube

Chemical analysis  - The samples are analysed on a Varian Saturn 2000 System using a 1079 injector that had been fitted with the ChromatoProbe kit. This kit allows the thermal desorption of small amounts of solids or liquids contained in quartz microvials (Micro-SPE, Amirav and Dagan, 1997; Wilkinson and Ladd, Varian Application note), or in the present case the thermal desorption of the trapped volatiles. The adsorbent tube is loaded into the probe, which is then inserted into the modified GC injector. The injector split vent is opened (1/20) and the injector heated to 40°C to flush any air from the system. The split vent is closed after 2 minutes and the injector is heated at 200°C/min, then held at 200°C for 4.2min, after which the split vent is opened (1/10) and the injector cooled down. A ZB-5 column (5% phenyl polysiloxane) is used for the analyses (60m long, inner diameter 0.25mm, film thickness 0.25µm, Phenomenex). Electronic flow control is used to maintain a constant helium carrier gas flow of 1.8ml min-1. The GC oven temperature is held for 7min at 40°C, then increased by 6°C per min to 250°C and held for 1min. The MS interface is 260°C and the ion trap works at 175°C. The mass spectra are taken at 70eV (in EI mode) with a scanning speed of 1 scan s-1 from m/z 30 to 350. The GC-MS data are processed using the Saturn Software package 5.2.1. Component identification is carried out using the NIST 02 mass spectral data base, or MassFinder 2.3, and confirmed by comparison of retention times with published data (Adams, 1995; Davies, 1990). Identification of individual components is confirmed by comparison of both mass spectrum and GC retention data with those of authentic standards.

ADAMS, R. P. 1995. Identification of essential oil components by gas chromatography/mass spectrometry. Allured Publishing Corporation, Carol Stream, Illinois, USA.

AMIRAV, A., AND S. DAGAN. 1997. A direct sample introduction device for mass spectrometry studies and GC-MS analysis. European Journal of Mass Spectrometry 3: 105-111.

DAVIES, N. W. 1990. Gas chromatographic retention indices of monoterpenes and sesquiterpenes on methyl silicone and Carbowax 20M phases. Journal of Chromatography 503: 1-24.

WILKINSON, S., AND P. LADD. Undated. The use of a solids inlet system to identify essential oils in anthers and leaves of flowering plants. Varian GC/MS Application note number 65. http://www.varianinc.com/image/vimage/docs/products/chrom/apps/gcms65.pdf