Is my lettuce contaminated with mercury? Might there be lead in the baby's food? Is that expensive wine a fake with added sweeteners? We're presenting the seven most important analytical methods to test food.
Chromatography is one of the best-known methods in food analytics. It analyzes what foods are composed of and detects additives and dangerous residues such as pesticides. Chromatography's principle is to separate a mixture of substances into its individual components.
- Gas chromatography (GC) – analyzing vaporizable samples with high sensitivity
- High performance liquid chromatography (HPLC) – suitable for non-vaporizable substances
- Mass spectrometry (MS) – tracking down molds
- Atomic absorption spectrometry (AAS) – identifying metals and metalloids fast
- Photometry – determining the nitrite content of prepared meat products
- Nuclear magnetic resonance (NMR) spectroscopy – detecting adulterated food
- NIR spectroscopy – analyzing the composition of food products
Gas chromatography (GC) – analyzing vaporizable samples with high sensitivity
In gas chromatography (GC), the mobile phase is a gas and the stationary phase usually a solid. This is how it works: an injector vaporizes a mixture so that the sample separates into its components, which then "fly", along with the gas, through a thin capillary (stationary phase) at different speeds. How quickly the components pass through the capillary is analyzed by a detector at the end of the separation system. The compound-specific retention times are used to identify not only residues such as pesticides and other contaminants, but also flavorings, sugar substitutes, fats and oils.
High performance liquid chromatography (HPLC) – suitable for non-vaporizable substances
Chromatography can also be made to work for substances that cannot be vaporized, but it takes a different analysis method: high-performance liquid chromatography (HPLC). Unlike in GC, the mobile phase is not a gas but a liquid, usually an eluent.
An injection syringe with an upstream valve initially dispenses the substance mixture onto a column containing the stationary phase. The components then use the eluent to race against each other towards the detector. As in gas chromatography, food additives and contaminants can be identified via their retention time.
The world’s largest Market Overview for HPLC/UHPLC systems shows all relevant manufacturers and their products.
Mass spectrometry (MS) – tracking down molds
Like GC and HPLC, mass spectrometry (MS) is an essential tool in food analytics. It is one of the most frequently used methods for identifying organic and inorganic substances. Mass spectrometry is often coupled with GC or HPLC. LC-MS, for example, has become the standard method to detect the toxins that molds on grains and fruits produce, known as mycotoxins.
The world’s largest Market Overview for Mass Spectrometers shows all relevant manufacturers and their products.
Atomic absorption spectrometry (AAS) – identifying metals and metalloids fast
Atomic absorption spectrometry (AAS) is a further method to determine organic and inorganic substances in food. A sample in an aerosol state flows with an inert gas, such as argon. Inductive coupling heats the gas stream up to 10,000 degrees Celsius. At this extreme temperature, the aerosol evaporates. This results in free atoms and ions that emit radiation.
Each chemical element has a characteristic line spectrum, so a differential spectrum will allow conclusions about the elements contained in the sample. AAS is a proven and fast method for identifying elements such as metals and metalloids in aqueous solutions and solids. Another option is detection by a mass spectrometer (ICP-MS) in combination with liquid chromatography (LC). Coupled LC-ICP-MS has particularly low limits of quantification.
Photometry – determining the nitrite content of prepared meat products
Photometry can identify ingredients in foods based on the fact that different frequencies of electromagnetic waves produce different colors. How? Simply put, photometry instruments sends a beam of light through a sample in a solution.
A detector identifies which light beams exit at the other end and which are absorbed by the solution. This opacity is called extinction, which is used to calculate which substances are contained in a food sample. For example, photometry helps to determine the nitrite content in sausages and other prepared meat products.
Nuclear magnetic resonance (NMR) spectroscopy – detecting adulterated food
Adulteration is becoming more widespread in the global food market. Particularly affected are high-priced wines, honey and olive oil. A well-known food analysis method to track down this form of racketeering is nuclear magnetic resonance (NMR) spectroscopy.
NMR systems measure how magnetically active atomic species, such as the isotopes hydrogen-1 or carbon-13, react to a radiofrequency pulse in a magnetic field. The resulting signals reveal the chemical environment of these atoms and thus the identity of the substances contained in food. Whether a product is adulterated or not can be easily determined by comparing its NMR spectrum with that of a reference product.
The great advantage of NMR spectroscopy is that dozens of molecule types can be identified and quantified simultaneously in a single measurement without first having to subject the food sample to chromatographic separation. Typical markers in the spectrum help to detect advanced spoilage or excessive thermal treatment.
NIR spectroscopy – analyzing the composition of food products
Near infrared (NIR) spectroscopy is another method to analyze food. The instruments work with light wavelengths between 800 and 2500 nanometers and thus between the visible (VIS) and the mid-infrared (IR) spectral range. NIR radiation excites the molecules in a food sample and thus makes them oscillate, and the reflected spectra reveal information about the molecular composition of the food. This helps to determine whether the composition of a food product is as specified – for example, its fat, protein and carbohydrate content.
The world's largest market overview of NIR spectrometers shows all relevant manufacturers and their products.