S P I C E
Direct Headspace Enrichment on GC Columns Rather than
Packed Traps or Fibers to Optimize Sensitivity and Quantitative
Recovery of Volatile Constituents
HS7900CTS
Headspace System
The HS7900CTS uses capillary traps rather than packed traps or qualitative diffusion onto fibers to provide a more quantitative and reproducible way to measure aromas, fragrances, and odors in consumer products. SPICE, or Solid Phase Incremental Capillary Extraction, uses multiple GC columns of increasing chemical affinities to trap compounds over a very wide boiling point range without the limitation of packed traps. With the introduction of GC capillary columns in the late 1970s, Gas Chromatography instrumentation transitioned to use capillary columns amazingly fast, as virtually everything about gas chromatography was improved by moving to open tubular capillary columns coated with the appropriate phase. With the introduction of PLOT Columns that added a more adsorptive layer to the walls of capillary columns, the need for packed GC columns diminished even further. Resolution, reproducibility, column consistency, reliability, sensitivity, longevity, and recovery from overloading were all dramatically improved. Until now, however, sample preparation and injection into low flow capillary GCs has not utilized the same amazing technology to optimize how the sample is handled prior to the GCMS. GCxGC uses a first capillary column to rapidly inject samples into a second GC column, and SPME essentially uses Inside-out GC columns for diffusive sampling, but no solutions have emerged that use GC capillary columns for multi-bed trapping and reverse elution until now.
S P I C E
Solid Phase Incremental Capillary Extraction
The SPICE technique uses 3 separate capillary columns in series with increasing strength to trap compounds boiling from -45 °C to over 350 °C. Alternatively, a 2 column trap is also available to eliminate Ethanol while retaining heavier compounds when analyzing alcohol containing samples. After primary trapping, and second SPICE trap further focuses the sample for incredibly fast injection into a GCMS for maximum sensitivity and compound resolution. Just as capillary columns operate at lower flow rates, capillary traps can rapidly desorb a sample at these lower flow rates as well, thereby making splitting an option rather than a requirement. The smaller particle size used in PLOT columns compared to packed traps allows much faster elimination of water vapor, resulting in virtually no impact on GCMS response even when at 100% saturation in samples. Two different versions of SPICE are implemented on the HS7900CTS
Large Volume Static Headspace SPICE (LV-SPICE)
LV-SPICE uses large sample vials (40, 500, 2000mL) to answer the question “what is that smell?” Extraction techniques such as Dynamic Headspace (DHS) do not answer this, because heavier compounds continue to be enriched during the sweeping process to be over-represented in the analysis. If only 1% of compound A but a full 23% of compound B are in the headspace at equilibrium (in a container of cosmetics or a bag of potato chips), then this is what needs to be delivered to the trapping system. Delivering 2% of compound A instead of 1% would be a 100% error in the determination, so a headspace “snapshot” is needed while under static equilibrium. LV-SPICE uses large containers to allow samples to come to equilibrium prior to quickly drawing a specific volume of headspace into the CTS trap, from 1cc to 250cc or more, without adding any purge gas to the sample that would otherwise take the headspace out of equilibrium with the liquid or solid sample. With today’s high sensitivity GCMS (GCMSMS) systems, typically only 10-50cc of equilibrated headspace is needed to reach even the lowest olfactory detection limits at low part per trillion levels, so a virtual snapshot of the headspace can be achieved in a SPICE trapping event lasting 2 minutes or less, with very little pressure change in the equilibrated headspace of a large vial.
Vacuum SPICE (V-SPICE)
V-SPICE offers a more quantitative and sensitive alternative to SPME, for every HS-SPME application. Samples from 0.1-20g are placed in either 2mL or 40mL vials. During extraction, the S7900CTS rail moves the sample in close proximity to the Capillary Trapping System (CTS), and the entire headspace is drawn through the primary CTS trap, with a vacuum drawing down to the boiling point of the matrix, as low as 0.1 psi absolute. The evolving matrix then continues to sweep the volatile chemicals through the short, ceramic coated heated stainless transfer line to the primary capillary trap, where water passes through virtually unretained. Alternatively, a small pulsed purge of UHP N2 or He can add additional flow to speed up the transfer to the capillary traps. Internal standards can be added directly to the primary SPICE trap and surrogates to the sample itself prior to extraction, but due to the completeness of most extractions, isotope dilution is generally unnecessary. The sample is reverse eluted to a SPICE focusing trap containing shorter segments of the same capillary columns, allowing fast injection to the capillary GCMS. Carryover with this solution is typically less than 0.1%, and often less than 0.01%.
V-SPICE Chromatogram
LV-SPICE Chromatogram
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