[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.

Impurities can however damage the body and must be present in or on foodstuffs only in harmless and technologically unavoidable quantities. Corresponding limit and tolerance values are defined in the Swiss Legislature in the Ordinance of the Swiss Federal Department of Home Affairs over Foreign Substances and Ingredients in Food Products (Fremd- und Inhaltsstoffverordnung, FIV) from 26th of June 1995 (updated 1st October 2015).

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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Susanne Täuber
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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


Les équipements de production sont souvent nettoyés à l'acide nitrique. Dans le cas où les processus de rinçage ne sont pas suffisants après le nettoyage, des résidus d'acide nitrique sont identifiables dans les denrées alimentaires par une teneur élevée en nitrates. Des bactéries peuvent décomposer les nitrates en nitrites, auxquelles les nourrissons sont particulièrement vulnérables, ce qui peut entraîner une méthémoglobinémie. L'eau potable de régions très agricoles peut également présenter des taux élevés de nitrites et de nitrates, ainsi que les légumes (comme les épinards, la mâche, le fenouil, etc.)


Les nitrosamines sont des composés hautement cancérigènes, qui peuvent se former dans les denrées alimentaires à la suite d'une réaction de substances nitrosantes, comme les nitrites, à la présence d'amines présentes dans de nombreuses denrées alimentaires. La bière, le café de malte et les viandes salées, mais également certains cosmétiques, peuvent contenir des nitrosamines qui peuvent être éliminés durant la production par le biais de modifications techniques.

Composés d'ammonium quaternaire

Vous trouverez ici de plus amples informations concernant les composés d'ammonium quaternaire présents dans les produits laitiers.

POP (persistent organic pollutants)

Lors de la convention de Stockholm de 2004, l'utilisation de substances chimiques présentant des propriétés persistantes, bioaccumulatives et ubiquitaires a été interdite ou restreinte. La liste d'origine contenant 12 substances (les « douze poisons ») a, entretemps, été complétée par de nouvelles substances. En font notamment partie les classes de substances des PFC (hydrocarbures perfluorés) et des PBDE (phényl-oxyphényles polybromés).

Les PFC sont utilisés comme produits chimiques auxiliaires dans de nombreux produits de grande consommation comme les vêtements, le papier, etc. Les PDBE trouvent leur application en tant que matériel ignifugeant dans les matières plastiques et les appareils électroniques. En raison de la grande toxicité de chacun de ces POP, l'absence de ces substances devrait régulièrement être contrôlée dans les denrées alimentaires et aliments pour animaux, et surtout dans les produits d'origine animale fabriqués à base de poisson, de lait et de viande.

Composés organostanniques

Les composés organostanniques sont utilisés comme stabilisants thermiques et lumineux dans la fabrication du chlorure de polyvinyle (PVC). Certains composés sont également autorisés pour les plastiques en contact avec les denrées alimentaires et peuvent, de ce fait, migrer dans ces denrées. Il existe à cet effet des valeurs limites de migration destinées aux emballages de denrées alimentaires. L'utilisation de composés de triorganoétain dans les peintures d'antifouling pour bateaux a entretemps, en revanche, été interdite. L'analyse de composés organostanniques est effectuée par le biais d'une analyse multi-méthodes, essentiellement pour les produits de la pêche et les denrées alimentaires emballées avec ces composés.

Toxine botulique

La toxine botulique est une toxine bactérienne qui se forme à partir du Clostridium botulinum. Il s'agit du poison le plus puissant qui existe pour l'être humain. C'est pour cette raison qu'il ne doit être détecté dans aucune denrée alimentaire contrôlée par les méthodes de détection les plus sensibles, conformément à ce que fixe l'OSEC. Le Clostridium botulinum étant une bactérie anaérobie, les denrées alimentaires stockées dans des conditions anaérobies ou dont le milieu est légèrement acide ou neutre (comme les poissons non salés et les conserves de poisson, la mayonnaise, les conserves de fruits et de légumes) y sont particulièrement exposées.

Alcaloïdes d'ergot

Les alcaloïdes d'ergot sont des substances toxiques du Claviceps purpurea, qui peuvent parasiter les foins, graminées et céréales (le seigle, notamment). Les alcaloïdes d'ergot sont des poisons très puissants. Selon la dose ingérée, ceux-ci peuvent, chez l'être humain ainsi que chez les animaux, provoquer de très fortes crampes musculaires ou de terribles douleurs de brûlure dans les membres, qui deviennent ensuite insensibles et qui se nécrosent (feu de saint Antoine). De très fortes doses peuvent même entraîner la mort. Vous trouverez d'autres informations sur le sujet dans le chapitre des mycotoxines.

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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