|  | Radiation source The source of radiation often used in AAS is a hollow cathode lamp (HCL). The HCL consists of a glass tube containing an anode, cathode and a gas (usually argon or neon). The cathode is made of the element being measured. The lamp emits radiation specific for the metal in the cathode. For example, if the cathode is made of iron, an iron emission spectrum is produced. When this radiation passes through a sample containing iron atoms (atomizer), the radiation will be absorbed because it has exactly the right wavelength (energy) to initiate transition from the groundstate to the excited state (lock and key principle). Therefore, each element requires a different lamp. |  |

|  | Monochromator The monochromator selects the wavelength that is needed to determine the concentration of the element. |  |

|  | Detector The detector measures the intensity of light which passes the monochromator. The light energy is transformed directly to an electrical signal. |  |

|  | Amplifier / read out The electric signal sent by the detector is processed in the amplifier and sent to the read out system (computer). |  |

|  | Sample compartment and atomizer This is where the sample can be introduced. AAS requires that the atoms to be analyzed are in the gas phase. Ions in a sample solution are therefore vaporized in a high-temperature source such as a flame or graphite furnace. Flame-atomizers consist of a nebulizer and a burner. The nebulizer converts the solution into a fine mist or aerosol. Alternatively, the sample can be placed in a small graphite tube which is electrically heated to a temperature (2000-3000°C) high enough to produce volatilization and atomization (graphite furnace AAS). The tube is positioned in such a way that the radiation beam passes through the atomized sample. |  |

Title of page

So far you studied the general principles of atomic spectrometry. Now the first spectrometry method will be explained, which is Atomic Absorption Spectrometry (AAS).

After digestion of the food sample, ions of the elements are present in an acid solution. AAS requires that the ions of the elements formed after digestion are atomized. In AAS absorption of UV/VIS radiation by atoms is measured. The part in which the free atoms are formed is called the atomizer (see diagram below). The amount of light absorbed by the atoms is proportional to the concentration of the specific element in the solution. So first a calibration series is measured with known concentrations of the element. Next digested sample solutions can be measured. By drawing a calibration curve the unknown concentration in the sample can be determined.

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