B-590.71.191 [2022-09] Iron (Fe) – AAS

Cations include, among others, sodium, potassium, magnesium and calcium. Their role in beer production and product quality should not be underestimated. For example, this group is necessary for yeast growth and thus for the fermentation process. However, excessive concentrations, especially of the heavy metals, have an extremely detrimental effect on the stability and sensory impression of beer. Therefore, monitoring the concentrations of these elements within the process of beer production is essential. Elements, such as potassium and magnesium, are also important for human nutrition. Depending upon the concentration present in beer, various analysis methods, including gravimetry, complexometry and colorimetry, facilitate their detection and quantification. For low concentrations, atomic absorption spectrophotometry is the preferred analytical method. Various devices can be utilized for determining the cation content, and they are briefly described below.

Atomic absorption spectrophotometry (AAS) is based upon the phenomenon of resonance absorption.

An element-specific light source (e.g., hollow cathode lamp or gas emitting lamp) radiates through a space (e.g., flame or absorption cuvette) containing the absorption medium, namely the metal of the element to be measured, in a vaporized form. This method is based upon the fact that radiant energy causes the excitation of atoms from their base orbitals, which then absorb specific frequencies of light, resulting in characteristic spectra. The reduction in the resonance energy is proportional to the concentration of the element present and is separated from the other frequency lines originating from the light source by a monochromator. These data are subsequently transformed by a detector to an electrical signal that is recorded by the processing unit.

Atomic emission spectroscopy in conjunction with inductively coupled plasma (Inductively Coupled Plasma – Optical Emission Spectrometry, ICP-OES) is a technique used to determine and measure elements based upon the phenomenon of atomic emission. The solutions to be analyzed are nebulized and the resulting aerosol is transported by a carrier gas, which introduces it directly into inductively coupled plasma (ICP). There, the elements are excited to a higher energy state, causing emissions. The spectrometer separates these emissions into individual wavelengths, and the intensities of the spectral lines of the element are measured with detectors (photomultipliers). A quantitative measurement is possible by calibrating the instrument with reference solutions, whereas a linear relationship exists over a broad range (generally several orders of magnitude) between the intensities of the emission lines (spectra) and the concentrations of the elements. The elements can either be analyzed simultaneously or sequentially.

Inductively coupled plasma mass spectrometry (ICP-MS) is a robust, very sensitive method used in inorganic elemental analysis. It is employed, among other techniques, for trace elemental analysis of heavy metals, such as mercury, lead or cadmium. In ICP-MS, a high frequency electric current ionizes the argon gas, and the sample is heated to 5000–10,000 °C. In doing so, the atoms are ionized, and plasma is created. Finally, the ions generated in the plasma are accelerated in the direction of the analyzer of the mass spectrometer, where the individual elements and their isotopes are measured. With ICP-MS, the detection threshold for most of the elements in the periodic table is on the order of nanograms per liter (ng/l) or better. Moreover, this method is characterized by an extremely high linearity with quantitative determinations over a range spanning nine orders of magnitude (from grams to picograms per liter). Aside from quantitative analysis, the ICP-MS can also perform highly precise isotope analysis, in which case high resolution ICP mass spectrometers are employed.