Fragrances Johanna ScoulMartina Lippe

07.10.2014

Case Study

• At the beginning of the distillation of menthone made from natural menthol there is a „green/mossy“ note.

• The off-note is in the first distillation fraction -> lower boiling point than menthone

• Menthone made from artificial menthol does not have this issue.

• With a GC-MS analysis there is no peak visible which could explain the smell.

What is the off-note?

• 1.) The off-note is a totally different species than menthone – Very low concentration and is therefore not detected

• 2.) The off-note is an isomer of menthone – 4 Stereoisomers

• Menthones: minty odor• Isomenthones: slightly musty odor

– Diastereomers can be excluded as they should be separable by GC

– Enantiomer: make a chiral GC• -> Case 1.)H. Surburg; J. Panten,Common Fragrance and Flavor Materials: Preparation, Properties and Uses, 5 thedition, Wiley, 2006, p. 63.

Analytical strategies

• Get the off-note in good purity– Preparative gas chromatography • Purification method

– Spinning-band distillation• Difference in boiling point

Preparative GC

• Separate components for more advanced use– Requires a column with a larger diameter

• A detector is needed– FID (Flame Ionization Detector) -> for carbon – ECD (Electron Capture Detector) -> for halogenated

compounds– NPD (Nitrogen Phosphorus Detector) -> for nitrogen and

phosphorus– Human nose -> GC sniffing technique

GC sniffing technique

• Splitter at the outlet of the GC column – Detector – Sniffing device

• -> get the retention time of the off-note

http://sim-gmbh.de/en/gcms/sim-olfactory-detector.htmlhttp://resources.schoolscience.co.uk/ICI/16plus/smells/smellsch3pg2.html

GC/MS-detection

• GC– Mostly apolar stationary phase

• Separates according to boiling point -> possible to limit the mass range of the off-note

• MS– Mostly quadrupole

• High mass flow rates possible • Integration time for one mass is very short

– For better sensitivity the mass range should be limited

• -> Selected ion monitoring- Normally: 10-10 g, can be improved by a factor of 100

• -> maybe possible to see the off-note in the spectrum

Further Suggestions

• Different Ionisation Method (normally: electron impact)– Chemical ionisation with negative ions

• Different mass spectrometer- FT-ICR

• GC-GC– Two columns – Interface that samples or collects the effluent from the first

column and introducing it to the second column– Two separation mechanisms or temperatures– -> Separation is highly selective

http://www.pg.gda.pl/chem/CEEAM/Dokumenty/CEEAM_ksiazka/Chapters/chapter6.pdf

Spinning-band distillation

• Fractionating columns improves the separation by helping the mixed vapours to cool, condense and vaporize again (Raoult‘s law)

• Spinning-band distillation: use of a helical, rotating band (teflon or metal)

http://en.wikipedia.org/wiki/Fractionating_column

http://www.brinstruments.com/fractional-distillation/spinning-band-distillation.html

Strategies

Identification of the chemical structure of the off-note1)  NMR spectroscopy: 

- Information about the chemical structure and chemical environment of the molecules.But - We need mg to make the analysis.

Strategies

2) Tandem mass spectrometry (MS/MS):

- Triple quadrupole mass spectrometer q = cell for collision-induced dissociation

- Examine selectively the fragmentation of particular ions in a mixture of ions.

- Structural information => product ion scan. Inert gas for collision

Parent ion Daughter ion

Collision-induced fragmentation

Strategies

3) Gas Chromatography Infrared Spectrometry (GC-IR):

- Separation of a mixture by a gas chromatograph.

- The fractions containing a single compound are then steered towards a FTIR-spectrometer.

Allows to identify isomers

Strategies

• Advantages: Very sensitive

- Light pipes are heated in order to rid condensation and maximize path length for enhanced sensitivity

- The interferogram can be obtained in a very brief time using a matrix isolation:Compared with the light pipes, the limit of detection can be reduced by a factor of about 100

Obtaining clear spectra of a sample ng

Strategies

• Disadvantages: Very expensive

- Matrix isolation needs a gold-flat and 10-12 K

- Detector - highly sensitive

What are odor Threshold values (OTV)?

• The lowest concentration of a certain odor compound that is perceivable by the human sense of smell.

• Can be expressed as a concentration in water or in air.

• Optical isomers can have different detection thresholds and can be less perceivable for the human nose.

Odor threshold values

• Two major types of flavor thresholds can be distinguished:

- The absolute odor threshold: The minimum quantity of an odorant to become perceptible.

- The differential threshold: The minimum difference in odorant concentration that can be perceived as distinct.

Types of measurement

• Psychophysical measurements:- Single values obtained from a series of repetead

measurements carried out with one or several individuals.

Types of measurement

• The dynamic dilution olfactometry (EN13725 standard):Odor concentration and odor threshold determination (ou/m3 = odor units per cubic meter of air)

- Test sample: Ambient air, sampled continuously, batchwise from an odor-emitting source or an odorant-saturated gas.

- Olfactometer presents the odour sample diluted with odour-free air at precise ratios, to a panel of human assessors.

- The examiners selected with a standardized procedure performed using reference gases.

Types of measurement

• GC sniffing technique:

- Injection of different dilutions of a sample into the gas chromatograph until the perception of the substance at the sniffing port.

- When the detector indicates its elution from the GC column- At the correct retention time.

Thank you for your attention