Gerstel

Automated Internal Standard Addition⁺ (ISDP⁺) with SBSE in TD-GC-MS for Improved Precision in Flavor Compound Determination

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Introduction

The dietary supplements market is valued at over 150 billion dollars (U.S.) worldwide. Dietary supplements are manufactured products that come in many forms, such as pills, capsules, powders, liquids, or tablets. They are used to supplement a person’s diet. The nutrients can be synthetic or extracted from natural sources. Many of these products contain flavoring agents, making them more palatable.

Many flavor/fragrance compounds have low odor/taste thresholds. Small changes in concentration can have a major impact on customer acceptance of the final product. Off odors and flavors often result in customer complaints. Identification and quantification of flavor and off-flavor compounds in these product types are important for quality control, competitive analysis, and customer complaint samples.

GERSTEL Solutions for Flavor Analysis in Dietary Supplements

The GERSTEL MPS Robotic sampler with TDU 3.5⁺ option, GERSTEL CIS 4 Cooled Injection System with Liquid Nitrogen cooling option, GERSTEL ISDP⁺, and Agilent GC-MS are an excellent combination for the analysis of flavor compounds in dietary supplements.

Twister®

The GERSTEL Twister® is an extraction device used for Stir Bar Sorptive Extraction (SBSE). The Twister enables ultra-trace determination of organic compounds in aqueous and gaseous matrices. It consists of a magnetic stir bar coated in glass with an absorbent layer. After sampling, the Twister is placed in an empty TD tube and heated in a thermal desorption system to release the analytes of interest.

Digram of SBSE

Several phases are available, including PDMS, HLB-PDMS, DVB-PDMS, CWR/PDMS, and CWR-DVB-PDMS.

Twister Phases

The Twister provides several advantages for SBSE workflows:

  • Highly efficient extractions due to the large stationary phase volume, ppq to ppt detection limits
  • Extraction efficiencies are predictable (using TwisterCalc software) based on octanol/water partition coefficient (Log Kow)
  • Solventless extraction
  • More stationary phase than SPME, TF-SPME, or SPME Arrow
  • Multiple samples can be extracted in parallel
  • Mature technique with hundreds of literature references

Thermal Desorption

Thermal desorption is an injection technique for gas chromatography where a liquid, solid or sorbent packed tube is heated in a thermal desorber to release analytes into the GC carrier gas stream. As the sample is thermally desorbed, the analytes are trapped either cryogenically or on a packed bed. After analyte trapping is complete, the trap is rapidly heated to transfer the analytes onto the head of the GC column as a narrow band to provide optimum chromatographic performance.

The GERSTEL TD 3.5⁺ provides discrimination-free trapping of compounds without the need for valves and transfer lines. This is a requirement for the determination of unknown compounds (non-targeted analysis). The TD 3.5⁺ can be used with SPME, static headspace and liquid injections, direct thermal extraction of solid samples, desorption of sorbent tubes for air sampling, desorption of Twisters and TF-SPME devices, and any other thermal desorption application.

Internal Standard Dry Purge⁺ (ISDP⁺)

The GERSTEL ISDP⁺ is a fully automated solution for spiking TD 3.5⁺ tubes with liquid or gaseous standards. The dry purge function can be used to eliminate moisture from sorbent tubes or samples.

Key capabilities of the ISDP⁺ include:

  • Choice of liquid or gas standards
  • Automated tube spiking with variable volumes
  • Spiking in sampling direction just before analysis or in batch mode
  • Automated generation of calibration curves
  • Fast and efficient drying of tubes in sampling flow direction

Case Study: Flavor Compound Analysis in Dietary Supplements (AppNote 283)

In this study, the GERSTEL ISDP⁺ was used to automatically create calibration curves and spike a sorbent tube with a retention time index (RI) mix. RI mixes are routinely used to help with compound identification.

Calibration curve for ethyl butyrate.
The study also demonstrated good agreement between the experimental and literature retention time values for the compounds identified in the chromatograms. The calibration curves prepared with the ISDP⁺ showed excellent linearity with r2 values >0.999. A comparison between manually spiked tubes and tubes spiked with the ISDP⁺ showed better precision for the ISDP⁺ spiked tubes.
Precision (%) and recoveries for manual and automated spiking.

Twister extraction was shown to provide excellent profiles for the flavor compounds in the supplements. The large phase volume provides good recoveries for many compounds, and the high concentration factor results in low limits of detection.

Total ion chromatogram for raspberry flavor sample.

Conclusion

AppNote 283 demonstrates the use of the GERSTEL TD 3.5⁺ with ISDP⁺ as an automated workflow for accurate flavor compound determination. The ISDP⁺ can be used to automatically add both liquid and gas standards to a thermal desorption tube. It can also create calibration curves, which can be used for quantitation of air samples, TF-SPME and Twister extracts, or samples analyzed by direct thermal extraction.

Automation using the GERSTEL TD 3.5⁺ with ISDP⁺ results in improved precision, automated standard addition, and reproducible quantitation that reduce variability and increase confidence in analytical results.

Learn more about the ISDP⁺ for Flavor Applications:

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