Fragrances
Johanna Scoul
Martina 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, 5thedition, 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.html
http://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-note
1) 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
Daughter ion
Parent 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 odourfree 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