Vegetable Oils Using Gas Chromatography
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0. AD-0009-GC Application News GC January 2004 Analysis of Vegetable Oils using Gas Chromatography Cynthia Lahey, Novalina Lingga, Ph.D. Customer Support Centre, Shimadzu (Asia Pacific), Pte. Ltd. Fats and oils are parts of normal daily consumptions. As a major source of energy, fats and oils are considered as important nutrients in human diets. Lipids also provide insulation for our bodies, transport vitamins that are not soluble in the water, as well as supply the essential fatty acids. Fats and oils belong to a class of substance called lipids. Fats differ from oils only in the form they take at room temperature; fats are solid, whereas oils are liquid at room temperature. Almost all of commercially important fats and oils of animal or plant origin consist of the lipid class called triglycerides (or triacylglycerols), which are fatty acids linked by ester bonds to glycerol (see Figure 1 for the chemi'cal structure of triglycerides). H 0 I II H-C-O-C-R1 0 II H-C-O-C-R2 0 II H-C-O-C-R I 3 H Figure 1. General chemical structure of triglycerides, where R,, R, and R 3 are unbranched hydrocarbon chains. Gas chromatography (GC) can be used for analysing the lipid or fatty acid content of a vegetable oil. Typically, GC is suitable for the analysis of organic, non-ionic compounds that are vapourisable at 400) 0 c or less. Therefore, for the analysis oflipids in edible oils, normally derivatisation of the lipids into their more volatile derivatives is performed prior to GC analysis. However, GC can be used to analyse triglycerides or other components of oils that can be vapourised at 400°C or less, without prior derivatisation. Here we describe the analyses of a few vegetable oils by capillary gas chromatograph (GC). The analytical conditions are shown in Table 1. Due to the high boiling points of the triglycerides, the injection, column and detector temperatures must be kept higher than those used for general GC analyses. Most commercially available GCs allow for high injection and detector temperatures; Shimadzu GC-2010, for example, has a maximum temperature of 450°C for its injectors, column oven and FID (Flame Ionisation Detector). The limitation would come from the capillary column used for the analysis. Although generally GC capillary columns have maximum temperature limits of around 320°C or less, some capillary columns are designed to have high temperature resistance. Such capillary column was used in the current triglycerides analyses. The resulting chromatograms are shown in Figures 2 to 5. The main peaks in these chromatograms are likely to represent triglycerides, since triglycerides comprise the main components of a vegetable oil. In a gas chromatographic analysis, the components in a sample are identified by comparing the retention times of the peaks (the time at which the peaks are observed) in the sample chromatogram, to the retention times of standard compounds (compounds ofknown identity and purity). Table 1. Analytical Conditions Instrument Column Carrier gas Linear velocity Injector temp. Injection method Column temp Detector Detector temp. GC-2010 equipped with AOC-20i auto injector Rtx-65TG (30m x 0.25mm x O.lμm) Helium, 99.9995% purity 40cm/s (constant linear velocity) 365°C Split (Split ratio = 40) 50°C (0.5min) - 50°C!min - 350°c (Omin) - 1 °c/min - 365°C (5min) FID 365°C In the absence of suitable triglycerides standard compounds, different oil samples may be characterised by the different chromatographic patterns obtained under the same analytical conditions. SHIMADZU (Asia Pacific) Pte. Ltd.
Transcript of Vegetable Oils Using Gas Chromatography
0.
AD-0009-GC
Application News GC
January 2004
Analysis of Vegetable Oils using Gas Chromatography
Cynthia Lahey, Novalina Lingga, Ph.D. Customer Support Centre, Shimadzu (Asia Pacific), Pte. Ltd.
Fats and oils are parts of normal daily consumptions. As a major source of energy, fats and oils are considered as important nutrients in human diets. Lipids also provide insulation for our bodies, transport vitamins that are not soluble in the water, as well as supply the essential fatty acids.
Fats and oils belong to a class of substance called lipids. Fats differ from oils only in the form they take at room temperature; fats are solid, whereas oils are liquid at room temperature. Almost all of commercially important fats and oils of animal or plant origin consist of the lipid class called triglycerides (or triacylglycerols), which are fatty acids linked by ester bonds to glycerol (see Figure 1 for the chemi'cal structure of triglycerides).
H 0
I II H-C-O-C-R1
0
II H-C-O-C-R2
0
II H-C-O-C-R I 3
H
Figure 1. General chemical structure of triglycerides, where R,, R, and R3 are unbranched hydrocarbon chains.
Gas chromatography (GC) can be used for analysing the lipid or fatty acid content of a vegetable oil. Typically, GC is suitable for the analysis of organic, non-ionic compounds that are vapourisable at 400) 0c or less. Therefore, for the analysis oflipids in edible oils, normally derivatisation of the lipids into their more volatile derivatives is performed prior to GC analysis. However, GC can be used to analyse triglycerides or other components of oils that can be vapourised at 400°C or less, without prior derivatisation. Here we describe the analyses of a few vegetable oils by capillary gas chromatograph (GC). The analytical conditions are shown in Table 1.
Due to the high boiling points of the triglycerides, the
injection, column and detector temperatures must be kept higher than those used for general GC analyses. Most commercially available GCs allow for high injection and detector temperatures; Shimadzu GC-2010, for example, has a maximum temperature of 450°C for its injectors, column oven and FID (Flame Ionisation Detector). The limitation would come from the capillary column used for the analysis. Although generally GC capillary columns have maximum temperature limits of around 320°C or less, some capillary columns are designed to have high temperature resistance. Such capillary column was used in the current triglycerides analyses.
The resulting chromatograms are shown in Figures 2 to 5. The main peaks in these chromatograms are likely to represent triglycerides, since triglycerides comprise the main components of a vegetable oil.
In a gas chromatographic analysis, the components in a sample are identified by comparing the retention times of the peaks (the time at which the peaks are observed) in the sample chromatogram, to the retention times of standard compounds (compounds ofknown identity and purity).
Table 1. Analytical Conditions
Instrument
Column
Carrier gas Linear velocity
Injector temp. Injection method Column temp
Detector Detector temp.
GC-2010 equipped with AOC-20i auto injector Rtx-65TG (30m x 0.25mm x O.lµm) Helium, 99.9995% purity 40cm/ s ( constant linear velocity) 365°C Split (Split ratio = 40) 50°C (0.5min) - 50°C!min -350°c (Omin) - 1 °c/min -365°C (5min) FID 365°C
In the absence of suitable triglycerides standard compounds, different oil samples may be characterised by the different chromatographic patterns obtained under the same analytical conditions.
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The chromatographic pattern can be discerned from the presence ( or absence) of peaks at particular retention times, and from the peak areas relative to the total peak areas (see Figure 6). These relative peak areas can be obtained by using the Normalisation quantitation method.
Alternatively, the patterns can also be compared visually. The GCsolution software allows comparison of multiple chromatographic patterns (see Figure 7). The present results show that the chromatographic profiles for canola oil, soya bean oil, olive oil and sunflower oil are sufficiently different for identification of the oils based on their chromatographic profiles.
uV xIO 000 TG O 15 Canola.gcd
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Figure 2. Chromatogram ofCanola Oil
uV xlOOOOO TG 0570live oil I uL.gcd
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0.5
0.25
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Figure 4. Chromatogram of Olive Oil
REFERENCE: 1. Shimadzu Analysis Guidebook, Food Product
Analyses, p.9 2. http://scholar.hw.ac.uk/site/chemistry
http://scifun.chem.wisc.edu/chemweek/Fats0ils/ Fats&Oils.html
uV xIO 000 TG 021 Soyabean.gcd
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Figure 3. Chromatogram of Soya Bean Oil
uV xlOOOO TG 060 Sunflower oil I uL. cd 6.
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12.5 15.0 min
Figure 5. Chromatogram of Sunflower Oil
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Pealtl Ret.T;,.., Area Cone. Unil 1 13.849 88125.5 4.37462 % 1 16.015 79241.4 7.40204 % 2 14.178 21785.0 1.08143 % 2 16.490 73759.3 6.88996 % 3 15.601 35983.8 1. 78627 % 3 17.011 36487.7 3.40837 % 4 16.013 612389.1 30.39947 % 4 18.174 32062.6 2.99501 % 5 16.394 89266.4 4.43126 % 5 18.623 379296.1 35.43057 % 6 18.087 76232.9 3.78426 % 6 18.728 42812.6 3.99918 % 7 18.121 54103.9 268576 % 7 19.224 283312.4 26.46460 % 8 18.617 934943.7 46.41133 % 8 19.830 143561 .4 13.41027 % 9 19.078 101~._()4562 %
Figure 6. Chromatographic pattern comparison based on relative peak areas.
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Figure 7. Comparison of chromatogram profiles.
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