GC-MS analysis of edible oils – authenticity, contaminants, adulterants, pesticides.

Edible Oils - Sunflowers

Sunflowers in a field, all natural or sprayed with pesticides and petrol fumes?

Edible oils form part of our cuisine, as natural to us as breathing. A well laid table will often include salt, pepper and olive oil. Edible oils can either come from animal sources, such as cows, pigs, ducks or from seeds and nuts such as sunflowers, canola, olives or peanuts. Oils from animals sources such as lard or beef drippings have fallen out of favour due to their high levels of saturated fatty acids and cholesterol. In contrast, vegetable oils are full of unsaturated fatty acids. So, why perform GC-MS analyses on these? Why worry about their purity and origin? Simple:

  • Pesticides spraying to promote crop yields
  • Environmental factors such as proximity to pollution sources (contaminants)
  • Addition of chemicals to change the quality of the oil (adulterants)
  • Plain simple fraud.
  • Religious reasons – is the oil kosher or halal?

Kosher/halal oil, seriously?

Think of a sausage, it has to be cooked, but still moist. How does one achieve this? By adding fat to the sausage. If you add in beef fat, Hindus cannot eat it, add in lard and Muslims or Jews will have a problem. There have been several food scandals over the years such as well known fast food outlets cooking their fries in lard, or mutton sausages laced with beef tallow. These crimes hurt us on a deep level as we trust the food manufacturers to provide a suitable, safe product.

So, how do we test for these? Our competitors are finally catching up to us! Remember that animal fats are made up of saturated fatty acids? Each meat type has a specific fatty acid profile, which can be converted to fatty acid methyl esters and analysed by GC-MS. This short presentation covers the differences between pig (lard), beef (tallow), chicken and mutton fat. Once you have identified the specific patterns of interest, nothing stops you from running these tests on a Pegasus BT, known for its speed, reliability and high levels of automation.

Food Fraud…

Food fraud is more common than we expect. After all, why not make a quick buck or two while we can? The most common fraud is to take a high-value oil and mimic it. For example, olive oil is highly prized for its health-promoting benefits. In a world overflowing with canola and sunflower oil, olive oil has been perceived as the go-to oil, especially when used in conjunction with a Mediterranean diet. After all, who would not want to live to be a 100?

While in many cases a cheaper oil is blended into olive oil (least problematic) or even coloured and flavoured to appear to be olive oil, these crimes are the least of our worries. Going a short step further, used oils from fast-food outlets have been recycled into olive oil through a simple process of filtering the oil, removing the odours adding the “olive oil” profile and colour. So, what is so bad about that? Used cooking oil can be carcinogenic as the repeated cycle of heating the oil, often to smoking point transforms it and in the process can trap free radicals in the oil.

Olive oil is a vegetable oil and therefore is high in unsaturated fatty acids. It has a very specific fatty acid pattern and therefore we can very easily test for the authenticity of the olive oil.

The great thing about using a LECO system to test for authenticity is that we can very easily automate the process, regardless of whether you have a high-resolution GC-MS or our entry level Benchtop system. In fact, once you know the pattern that is authentic, our fully automated reference algorithm adds less than a minute to your overall data processing method while allowing you to focus on other tasks.

Contaminants and adulterants

Contaminants come from a variety of sources, from simple issues such as cooking fires or coal-powered electricity generators to more complex indirect contamination from simply spraying water that was contaminated with industrial or municipal effluents. One analysis for 3-MCPD came about due to the chlorination of edible oils and the refining process which should remove these contaminants! In other words, the simple act of cleaning the oil makes it unfit for use (in this case). So, how does palm oil get chlorinated? Nature. Many palm oil plantations are near sea-level and a high wave would drench the fields with sea water, which contains salt (Sodium and Chlorine). Once in the oil, 3-MCPD is impossible to remove. In addition, 3-MCPD has an effect at trace levels, while the oil matrix will contaminate your ion source, unless you are using a LECO Pegasus system (BT or -C), in which case, you never have to worry!

Not all contaminants are toxic though. Some are just annoying to the end-user, based on their olfactory effect. Essentially, our noses are highly developed detectors and any contaminants, whether added in by accident, or indeed on purpose, or whether created by oxidation processes, will trigger a response in our sensory system. The list of possibilities is endless as any product that the oils have gotten in contact with could be the source of the contaminants.

The nature of contaminants add to the complexity of the analysis. Basically you are performing a non-routine, non-target analysis in many cases. This means that other Mass Spectrometers will fail as they are designed to perform routine, targeted analyses. The LECO systems, designed for performance under both routine and non-routine conditions remove any uncertainty.

Edibles oils by GC-MS, Pegasus BT, contaminants, adulteration, food safety, fraud.


Pesticides are normally the go-to chemicals where food is concerned and edible oils are certainly a potential vector for the presence of pesticides in our lives. We all love to eat fruits and vegetables that are perfect, unblemished and to achieve this, most farmers will use pesticides to control their environment. In most cases, you just wash the produce, or peel it and you are good to go. But, what if you need the oils of a lemon or an orange? Sounds far fetched? Yet many beverages require the peel of a lemon, which is full of the essential oils of a lemon… Look at the list of ingredients in some popular soft drinks, or in some well known liqueurs. On a more benign level, you can find challenges with simple produce such as sweets, fruit cakes and energy bars. The astounding part of this is that many of the most efficient pesticides are designed to be in oil, thus exacerbating the problem.

Oils also are a complex matrix to analyse and often you have to perform non-routine analyses in order to ensure that every possibility is catered for… a tall ask for any laboratory, unless you are equipped with a Pegasus system. Using the unique technology from LECO, you can be sure to find both target and non-target pesticides.

Edible Oil GC-MS analysis resources


Fatty Acid Methyl Esters (FAMEs). Note: Each of the FAME mix represents the accepted FAME pattern for a particular oil or fat.


LECO recommends using the Pegasus BT for routine analyses, the Pegasus BT 4D for non-routine or more complex matrices and the Pegasus HRT for highly-complex, non-routine analyses.

Application Notes