Gas chromatography-mass spectrometry.
Agilent 7820a
Applications
• Foods: GC:MS is extensively used to analyse free fatty acids,
sterols, esters, aromatic hydrocarbons and aldehydes.
• Perfumes and Essential oils: GC:MS can separate, closely
related molecules and distinguish between volatile alcohols
and terpenes.
• Hydrocarbons: GC:MS separates isomers with the same
molecular weight, distinguishing between structural
isomers and even cis/trans isomers.
• Environmental: GC:MS is routinely used in identifying
pesticide, organic pollutants and plastic contamination.
• Biofuels: GC:MS can analysis and quantify the components
of biofuels to establish whether they are a good substitute
for the petroleum industry.
Food Industry.
Analysis of Plant Oils.
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Free Fatty Acid (FFA) and Sterol Analysis by GC:MS.
Fatty acids and long chain sterols must be derivatized before injecting into the GC:MS.
This procedure involves a TMS agent and heating. The TMS agent is chosen according to the availability of
the oxygen atom to be derivatized. Hindered alcohol groups require a specialised agent and longer heating
times.
We use TMS reagents purchased from Regis Technologies.
http://www.registech.com/Markets/Chromatography/GCDerivatizationReagents/Silylation.html
We can advise on pre-analysis clean up of samples to achieve the best results.
Quantification can be achieved by internal and external standards.
Kovats index can be calculated for chromatographic peaks.
Mass Spectra synchronised with reliable databases and our own database.
Typical analysis of FFA and Sterols, on oils, nuts, seeds and other plant material.
TMS
Trimethyl
silanes
Cholesterol
Essential Oils and Perfumes
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Analysis of essential oil components.
By mass spectral fingerprint, Kovats Index and comparisons with reliable
databases.
These oils contain dozens if not hundreds of distinct compounds, some of which
are incredibly similar.
These molecules have the same molecular weight MW: 204.35 g/mol, but are
different compounds.
GC:MS will separate them.
Calculation of the Kovaks Index and the individual mass spectra aids in their
identification.
Zingiberene
Alpha cedrene
Beta caryophyllene
Characterization
of Essential Oils.
Chromatography peaks tell you when and how much compound you have.
The Mass Spectrum shows you the compounds fragmentation pattern, which acts as a molecular finger print.
The Kovats Index, provides a dimensionless unit for comparison with other databases.
Table Showing GC:MS Analysis Of 2 Oils
Dill
Geranium
Citronella Oil
GC: Retention
time
6.509
7.427
8.037
8.098
8.177
8.981
9.291
9.495
10.382
10.474
10.705
10.876
11.755
Lemon Oil
GC: Retention
Compound Name
time
Limonene
5.099
Linalool
5.197
neoiso-Isopulegol
5.411
Citronellal
5.769
Isopulegol
5.816
Citronellol
5.994
Geraniol
6.470
Geranial
6.517
Citronellyl Acetate
6.929
Eugenol
7.304
Geranyl Acetate
7.430
beta Elemene
7.489
Napthalene
7.882
11.83
beta Cubebene
7.937
11.989
12.215
12.466
12.749
13.274
alpha Muurolene
delta Cadinene
Hedycaryol
endo-1-bourbonanol
Guaiol
8.027
8.101
8.433
8.587
9.163
Compound Name
alpha Thujene
alpha Pinene
Camphene
Sabinene
beta Pinene
Myrcene
o-Cymene
Limonene
gamma Terpinene
alpha Terpinolene
Linalool
Nonanal
cis-Limonene oxide
trans-Limonene
oxide
Epoxyterpinolene
Citronellal
Terpinen-4-ol
alpha Terpineol
Citral
Lemon Grass
Kovats Index (KI).
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A dimensionless quantity that characterizes each GC:MS eluted compound,
according to a linear retention index and eradicates instrument variations e.g.
oven temperature, gas flow etc…….but not column differences.
The retention times of a known C7-C40 alkane standard is used to calibrate KI.
We have a software program that then generates the KI from the retention times
of the standard alkane above and below the analyte of interest .
Retention Times of Alkane Standard
Tea Tree
Reference Retention Times
Name
Octane
Nonane
Decane
Undecane
Dodecane
Triddecane
Tetradecane
Pentadecane
Hexadecane
Heptadecane
Octadecane
Nonadecane
Icosane
Henicosane
Docosane
Tricosane
Number of Carbons Retention Time
8
3.267
9
4.688
10
6.097
11
7.417
12
8.646
13
9.795
14
10.872
15
11.887
16
12.848
17
13.759
18
14.625
19
15.451
20
16.239
21
16.993
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17.715
23
18.406
Lavender
KI
Database Comparisons
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We have our own database.
GC:MS, Wiley database.
Pherobase. http://www.pherobase.com/
Nist Chemistry Webbook.
http://webbook.nist.gov/chemistry/
• http://lipidlibrary.aocs.org
• All excellent databases for comparison of mass
spectrums and KI index's.
Hydrocarbons
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We have various GC:MS methods for analysing hydrocarbons of different
volatilities.
Equivalent Carbon Length (ECL) can be generated, to establish the number of
carbons in each chromatographic peak. Mass Spectra and databases can then be
used to identify each chemical species.
APPLICATIONS:
Phthalates
Biofuels, insect pheromones, pesticides and herbicides.
Equivalent Carbon Lengths
ECLx = n + RTx-RTn/RTN-RTn
EQUIVALENT CARBON LENGTH.
A dimensionless quantity that characterizes each GC:MS eluted compound, according to a linear
retention index and eradicates instrument variations e.g. oven temperature, gas flow etc…….but
not column differences.
The retention times of a known C7-C40 alkane standard is used to calibrate ECL.
We have a software program that then generates the ECL numbers from the retention times of
the standard alkane above and below the chromatographic peak of interest.
Reference Retention Times
Name
Octane
Nonane
Decane
Undecane
Dodecane
Triddecane
Tetradecane
Pentadecane
Hexadecane
Heptadecane
Octadecane
Nonadecane
Icosane
Henicosane
Docosane
Tricosane
Number of Carbons Retention Time
8
3.267
9
4.688
10
6.097
11
7.417
12
8.646
13
9.795
14
10.872
15
11.887
16
12.848
17
13.759
18
14.625
19
15.451
20
16.239
21
16.993
22
17.715
23
18.406
ECL = Equivalent Carbon Length
RTn= lower molecular weight alkane retention
time.
RTN= higher molecular weight alkane retention
time.
RTx = retention time of species you are interested
in finding ECL for.
Retention Times of Alkane Standard
Similar to the KI, but often used for hydrocarbons and sometimes fatty acids.
GC:MS Detection Limit
• Generally, the HP GC:MS can detect chemical
species down to the 10ng per µL, quantities.
• If your analyte is below this concentration we
can get access to an, Agilent 5975 series MSD
• Agilent 7820A GC System.
• With a detection limit of the order, 1ng per µL,
depending on the chemical species.
Special Projects.
Centrifuge
• Garbage in Garbage OUT!
• We can advise on the best pre GC:MS clean up procedures.
• We have a number of solid phase extraction procedures (SPE)
we use to chemically separate sample components. As well as
liquid extractions.
• Physical extraction can also be achieved by centrifuge
techniques.
• For larger projects we can train and assist you, to use the
GC:MS instrument and achieve the best results.
Vacuum manifold, SPE
Procedures