Determination of Mercury by Cold Steam Atomic Absorption Spectrophotometry.
Explanation:
Since the mercury content in both potable and raw waters and in fish is generally at levels of concentration of parts per billion, it has been necessary to develop analytical methods with precision and accuracy that were sensitive enough to allow their analysis at such concentrations . The most used method for the analysis of mercury in water and fish is that of atomic absorption-cold steam that allows mercury analysis to be carried out with detection limits of 1 ppb.
Direct flame atomic absorption spectrophotometry (FAA) is an analytical technique that allows the detection and quantification of metals in solution. This technique is indicated to determine alkaline, alkaline earth and heavy metals elements present in any type of sample that can be dissolved.
The atomic absorption spectrophotometry is based on the ability of the elements, in their baseline atomic state, to absorb electromagnetic radiation at specific wavelengths for each element. The amount of energy absorbed is directly proportional to the concentration of the atoms of the analyzed metal, in accordance with the Lambert-Beer Law. The
Detection limits achieved are of the order of ppm (parts per million).  In this technique, dissolved metals are brought to their elementary atomic form by heating by a flame generated by a mixture of combustible gases. The most commonly used mixtures are: air-acetylene and nitrosoacetylene oxide. Flame temperatures range from 1900 ° C to 2800 ° C.
The atoms in the form of a gas cloud are irradiated by a beam of light of a specific wavelength, according to the analyzed metal; This is achieved by using cathode lamps of the metal of interest or with discharge lamps without electrode. The atoms absorb a fraction of the radiation coming from the lamp and the remaining fraction is captured by a photodetector and a transducer device, which converts it into an electrical signal, which is subsequently registered by a software.
As mentioned above, the signal value obtained is proportional to the concentration of the atoms present in the gas cloud; in this way it is possible to construct a calibration curve by analyzing standard solutions of known concentration and measuring the magnitude of the absorption of each of them.
A particular case in the atomic absorption technique is mercury, since thanks to its volatility, it does not require the use of flame to atomize and can be determined in the form of cold vapor. Through this technique, detection limits of the order of 1 ppb are reached.
The determination is made by adding a reducing agent (stannous chloride or sodium borohydride), to the digested. The reaction of mercury in solution with the reducing agent produces very volatile atomic mercury.
The mercury vapor is led to a cell placed in the passage of the light beam, where the interaction between the mercury atoms and the radiation occurs, taking place the absorption
