Two common accessories for the Thermo Scientific Atomic Absorption Spectrometer
Two common accessories for the Thermo Scientific Atomic Absorption Spectrometer
1. Atomic absorption graphite tube
In order to achieve the desired atomization conditions, there are four requirements for the graphite tube:
a. The material used to make the graphite tube must be high-density, high-strength, high-density graphite.
b. The geometry of the graphite tube should be reasonable and precision machining is required to ensure consistent machining accuracy and size.
c. The specific resistance value of the graphite tube has corresponding requirements for different instruments, to ensure the matching of the specific resistance value required by the instrument, and to ensure uniformity of the specific resistance value of the graphite tube produced in batch.
d. Like the material, shape and specific resistance of the graphite tube, its surface characteristics play a decisive role. In order to prevent atomic penetration, prevent diffusion loss, improve sensitivity, enhance oxidation resistance, and improve life, pyrolysis coating is performed on the surface of the graphite tube, or impregnated with a compound such as molybdenum, tungsten or ruthenium to form a metal carbide.
Second, atomic absorption hollow cathode lamp
A glow discharge is generated when a voltage of 200V-500V is applied between the two poles. Under the action of an electric field, electrons collide with the carrier gas atoms and ionize them on the way to the anode, releasing secondary electrons, increasing the number of electrons and positive ions to maintain the discharge. Positive ions derive kinetic energy from the electric field. If the kinetic energy of the positive ion is sufficient to overcome the lattice energy of the surface of the metal cathode, when it strikes the surface of the cathode, the atom can be sputtered out of the crystal lattice. In addition to sputtering, the heating of the cathode also causes thermal evaporation of elements on the surface of the cathode. The atoms sputtered and evaporated enter the cavity, and are excited by a second type of collision with electrons, atoms, ions, etc., and emit resonance radiation of the characteristics of the corresponding elements.
1 Note that the polarity cannot be reversed.
2 In order to stabilize the luminous intensity of the lamp, preheat for 10-30 min at the working current.
3 lamps are not used for a long time, should be ignited regularly, generally preheated for 1h under working current.
4 Long-term shelving, there are impurities in the lamp, and the reverse gas removal method can be used. Reverse the electrode with a large current for 30min.
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