[Translate to english:] Fremdstoffanalytik: Probenvorbereitung

Foreign Substances

Analysis of impurities in foodstuffs

Foodstuffs consist of a variety of components. These include nutrientsadditives as well as further diverse, natural ingredients. Foodstuffs can also however contain unwanted components, so-called foreign substances or impurities Nutrients such as fat and carbohydrates supply the body with energy while additives such as preservatives and emulsifiers are added to the foodstuffs primarily for technological reasons.

Foreign substances can, however, be harmful to the body and are permitted in or on foodstuffs only in quantities that are harmless to health and are technically unavoidable. Corresponding maximum values are laid down in the Contaminants Ordinance (VHK), among others.

Would you like to know which investigations are necessary to ensure the harmlessness and the marketability of your products? We would be happy to advise you which analyses could provide you with a suitable statement for classification of the quality of your foodstuffs.

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Head of Order Management Food & Feed Services

Sascha Theobald

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How do impurities get into foodstuffs?

There are a number of ways impurities can get into foodstuffs, for example from the environment, from contaminated raw materials, during production or from migration out of the packaging. They are unwanted in foodstuffs and can damage the health of consumers depending on their concentration. 
As a result, it is sensible to regularly monitor for protection of the consumer, to ensure compliance with legal regulations and to check the company’s Good Manufacturing Practice.

Impurities can also enter into products from the packaging or from how they are printed
Impurities can also enter into products from the packaging or from how they are printed

Different impurities

The list of impurities that could potentially occur is long. Depending on the analytical issue, customer-specific analysis processes can be used alongside the standard methods. You can find a list of common impurities here.


You can find detailed information here on pesticide analysis.

Heavy Metals

You can find detailed information here on heavy metal analysis.


You can find detailed information here on Mycotoxins.

Biogenic Amines

You can find further information here on biogenic amines in milk products.

DCD - 2-Cyanoguanidine

You can find further information here on DCD in milk products.


Dioxins, dioxin-like PCB and Ballschmiter PCB

Dioxins and Polychlorinated biphenyls (PCB) are ubiquitously present as environmental pollutants and accumulate due to their fat solubility in foodstuffs containing high levels of fat as very poorly degradable contaminants in the food chain.

Because numerous toxic effects of dioxins and PCB have been demonstrated, there exist in both the Swiss and the EU legislature, matrix-specific maximum limits, for example for meat and meat products, milk products, baby foods, vegetable fats and oils and so on.

These maximum limits are defined here as so-called toxicity equivalents (TEQ), i.e. they take account of the very different levels of toxicity of individual compounds by multiplying the absolute content by a toxicity factor.


In the case of small amounts of hydrocarbons detected in foodstuffs, they mostly occur from unintended contamination, e.g. from migration out of the packaging or printing inks from the labelling. Higher concentration would indicate a possible lubricating oil contamination during production or contaminated raw materials such as fats or oils. Analytical testing can determine the length of the carbon chains of the hydrocarbons detected and also enables additional differentiation of the hydrocarbons into MOSH (mineral oil saturated hydrocarbons; saturated hydrocarbons from petroleum oil such as paraffin), POSH (polyolefin oligomeric saturated hydrocarbons; saturated hydrocarbons oligomers from polyolefins such as polypropylene) and MOAH (mineral oil aromatic hydrocarbons; hydrocarbons from petroleum that consist of highly alkylated aromatic rings). This information is important with regards to an estimation of the toxicity in foodstuffs.

Minimisation of the hydrocarbon content by optimisation of the production process should be strived for as part of Good Manufacturing Practice. In particular, cooking fats, butter and other products containing large amounts of fats absorb hydrocarbons from the packaging quickly. Due to the complex evaluation of the toxicity of many hydrocarbons, until now tolerance levels have only been legally defined for thick-skinned fruits of 10 mg/kg (migration from jute bags). The problem, however, is very topical and it should probably be expected that tolerance and limit values will be legally defined in the future.

Polycyclic aromatic hydrocarbons (PAHs)

PAHs arise primarily from the burning of organic materials (such as fats) with a lack of oxygen. That means that all manufacturing and treatment processes in which foodstuffs are strongly heated or come into contact with combustion gases or smoke could lead to the formation of PAHs.

There are also other methods of contamination. Nuts are often transported in jute bags which are made supple by the use of petroleum products. Both an increased level of PAH and levels of aliphatic hydrocarbons can be detected in foodstuffs as a result of migration.

PAHs are also known to be organic environmental contaminants that can accumulate in foodstuffs (e.g. volcanic soils, contaminated waters and so on).

PAHs are in part carcinogenic contaminants that, in an ideal world, are not detectable in foodstuffs. A tolerance level of a maximum of 2 µg/kg exists in Switzerland for cooking oils for the lead substance Benzo(a)pyrene. In the EU, statutory regulation takes place via the so-called “PAK4”: The PAK4 are the compounds Benzo(a)pyrene, Benz(a)anthracene, Benzo(b)fluoranthene and Chrysene. The EU Regulation No. 835/2011 amendment of EU Regulation No. 1881/2006 has been valid since September 2012 and contains maximum levels for a range of foodstuff groups (cooking fats and oils, smoked meat products, baby foods and so on). The legal regulation takes place as a so-called “lower bound concentration”, i.e. the results of the four individual substances named above will be classified as “zero” when they fall underneath the limit of determination. The requirement on the determination limit for the four substances is 0.9 µg/kg in accordance with EU Regulation No. 836/2011. It is analytically possible to investigate the PAK4 within the framework of a multi-method that identifies 12 substances in total.


Acrylamide is a reaction product that occurs with the heating of foodstuffs that contain both reducing sugars such as fructose and glucose and the amino acid asparagine. Because acrylamide is a carcinogenic substance, the principle of minimisation is valid.

Product specific signal values exist for the evaluation of Good Manufacturing Practice, e.g. for a range of cereal products such as crispbread and breakfast cereals, for potato products like crisps and prepared french fries and for coffee products such as soluble instant coffee and roasted coffee.

Acrylamide is an impurity which can be found in starchy and strongly heated foodstuffs such as chips
Acrylamide is an impurity which can be found in starchy and strongly heated foodstuffs such as chips

3-monochloropropane-1,2-diol (3-MPCD), 3-MCPD-ester and glycidol ester

3-MCPD occurs when fat and salt containing foodstuffs are treated with high temperatures in the manufacturing process (e.g. seasoned sauces and highly heated baking products). 3-MCPD in animal experiments leads to an increase in the number of cells (hyperplasia) in renal tubules and causes a considerable number of benign tumours. In the Swiss Ordinance on Foreign Substances and Ingredients in Food Products (FIV), there is a tolerance value of 0.2 mg/kg for liquid seasoned sauces.

3-MCPD-ester are compounds of 3-MCPD and various fatty acids that are formed at high temperatures and dehydration by a reaction of fats and chloride ions. Glycidol esters occurs in the absence of chloride ions. Both compounds appear in all refined vegetable oils and fats as well as foodstuffs that are manufactured from them such as baby foods or margarine. They can release 3-MCPD into the human organism so it should be attempted to minimise their presence by optimising the production process.


Antibiotics may be used in the keeping of animals to treat infections or to keep the danger of infection for the working animals low. In fruit cultivation, they are used for combating fire blight. Bacteria can develop resistance from the intensive use of antibiotics. As a result, antibiotic residues must not be detectable in foodstuffs.


Radionuclides occur in both plant-based and animal-based foodstuffs, whereby distinctions are made between natural radioactivity such as potassium-40 and artificial radioactivity such as caesium-137. The level of radionuclide concentrations in foodstuffs depends, among other factors, on the radioactivity of the source media (soils, water) and other conditions at the location of the plant or animal production. In the legislature, there are tolerance and limit values defined for the various radionuclides depending on the foodstuffs present. Increased values sometimes occur in wild mushrooms and game.

Volatile chlorinated hydrocarbons

The production facilities for foodstuffs are frequently disinfected with active chlorine. Residues of active chlorine, for example from insufficient rinsing after disinfection can lead to it being spread into foodstuffs. There, the active chlorine residues can form volatile halogenated hydrocarbons such as chloroform with the product. Because some of these compounds are carcinogenic and could also cause organ damage to the liver and kidneys, there is a tolerance value in the Swiss Ordinance on Foreign Substances and Ingredients in Food Products (FIV) that is valid for all foodstuffs.

Solvent residues

Solvents such as hexane isomers, propanol or butanol are sometimes used for the extraction and production of cooking oils from grains as well as natural flavouring agents. Solvent residues can get into foodstuffs from these ingredients. Due to the toxic characteristics of solvents, specific tolerance levels are given in the legislature which are dependent on the solvents identified and the foodstuff matrix that is present.

The determination of solvent residues on gas chromatographs
The determination of solvent residues on gas chromatographs


Often, production facilities are cleaned with nitric acid. If the rinsing process after cleaning is not sufficient, then the residues of the nitric acid will be noticeable due to an increased level of nitrates in the foodstuffs. Nitrate can be degraded by bacteria into nitrite that babies in particular are very sensitive to and which can lead to methaemoglobinaemia. Drinking water in heavily agricultural areas can also exhibit increased levels of nitrate and nitrite, as can vegetables (e.g. spinach, lamb’s lettuce, fennel etc.).


Nitrosamines are very highly carcinogenic compounds which can occur in foodstuffs from the reaction of nitrosating objects such as nitrite with the amines that occur in many foodstuffs. In particular, beers, malt coffees, and cured meat products but also cosmetic products can show nitrosamine that must be eliminated by technical alterations during the production.

Quarternary ammonium compounds

You can find further information on quaternary ammonium compounds in milk products.

POPs (Persitent Organic Pollutants)

In the Stockholm Convention of 2004, the use of substances with persistent, bioaccumulative and ubiquitous characteristics was forbidden or restricted. The original 12 substances (the “Dirty Dozen”) has in the meantime been expanded to include further substances. Among others, substances of the classes PFCs (perfluorinated chemicals) and PBDEs (polybrominated diphenyl ethers) are ranked here.

PFCs are used as chemical aids in numerous consumer products such as clothing and paper. PBDEs find use as flame retardants in plastics and electronic devices. Due to the high level of toxicity of certain POPs, the absence of these substances should be monitored regularly in foodstuffs and feed and in particular in animal products such as meat, milk and fish products.

Organostannic compounds

Organostannic compounds are used as heat and light stabilisers in the manufacturing of polyvinyl chloride (PVC). Individual compounds are also permitted for plastics that have contact with foodstuffs and can migrate into foodstuffs through this route. As a result, there are migration limits for foodstuff packaging. The usage of tri-substituted organostannic compounds as an antifouling paint for ships’ paint is however nowadays forbidden. The analysis of organostannic compounds is performed by using a multi-method, primarily for fish products and foodstuffs that are packed correspondingly.

Botulinus toxin  

Botulinus toxin is a bacterial toxin that is formed from Clostridium botulinum. It is the most powerful poison that is known to man. As a result, in accordance with the Swiss Ordinance on Foreign Substances and Ingredients in Food Products (FIV), it must not be detectable in any foodstuff with the most sensitive methods of detection. Because Clostridium botulinum is an anaerobic bacteria, the foodstuffs primarily endangered are those that are stored in anaerobic conditions and whose surroundings are only slightly acidic or neutral (e.g. non cured canned meat and fish, mayonnaise and canned fruits and vegetables).

Ergot alkaloids 

Ergot alkaloids are toxins of the ergot fungus Claviceps purpurea that can occur as a parasite on forage grasses and sweet grasses as well as on grains (particularly on rye). Ergot alkaloids are very strong poisons. Depending on the dose ingested, by animals as well as humans, this could lead to severe muscle cramps or to burning pains in the limbs that then later become numb and could die off (Saint Anthony’s Fire). Very high doses could even lead to death. You can find further information with the Mycotoxins.

Mycotoxins (here, ergot) also rank among the impurities
Mycotoxins (here, ergot) also rank among the impurities

Identification of foreign substances

Unknown foreign substances continually make their way into the production process of foodstuffs and are then separated from the foodstuffs there by production engineering measures. Identification of the foreign substances is sensible to find the cause of these contaminations and to prevent them from happening in the future. This is often analytically possible through a combination of diverse methods such as X-ray fluorescence analysis, microscopy, ICP-MS and infrared spectroscopy.

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Sample preparation for the determination of pesticides
Sample preparation for the determination of pesticides

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