Atomic absorption spectroscopy. In this experiment, the characteristics of flame ASS instrumentation will be explored. Pb and Mg calibrate curve will be investigated.

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Gas chromatography

Atomic absorption spectroscopy

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Aim

In this experiment, the characteristics of flame ASS instrumentation will be explored. Pb and Mg calibrate curve will be investigated. Different condition will be used, such as different ion interference, different flame and background effects. All solution will be carried out in low concentration (ppm).

Theory

Atomic-absorption spectroscopy (AAS) is based on the absorption of light to measure the concentration of compound. The samples are usually liquids or solids, the analyte atoms or ions are vaporized in a flame or graphite furnace. The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. The analyte concentration is determined from the amount of absorption. The evaluation of ASS measurements is also similar to the UV-Vis spectrophotometry, because it is based on Beer’s Law, which says that the absorption of light is directly proportional to the number of atoms absorbing it. The more concentrated the sample solution is, the higher absorbance is measured. []

All atoms have energy. Under normal conditions, atoms exist in their most stable states. So we cannot measure the energy state for an atom. we only can measure it when we change its energy. Adding thermal energy (heat) can cause an atom to increase to a higher energy state. This is the basic principle of AAS.

Figure 1 shows the AAS progress. The widely used atomizer is flame. First, the sample solution is aspirated by a pneumatic nebulizer, transformed into an aerosol, which is introduced into a spray chamber, where it is mixed with the flame gases. Second, the monochromator detect the flame (this part is similar to UV spectrophotometer). Then, computer shows the graph and figures.[, ]

Figure 1. Atomic absorption spectrometer block diagram

AAS usually determines the metals in liquid. Metals include Fe, Cu, Al, Pb, Ca, Zn, Cd and many more. It also measures the concentrations of metals in the samples. Typical concentrations range in the low mg/L range.

Procedure

preparation of solution

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  1. Prepare solutions containing 5, 10, 15,20,and 25 ppm Pb by dilution of 1000ppm Pb.
  2. Prepare solutions containing 2.5, 5,10, 15 and 20 ppm Mg.
  3. Measure the Pb standard solution in 217nm 1nm slit width.
  4. Measure the Mg standard solution in 202.6nm with 1nm slit width.

Effect of slit width

  1. Set the wavelength to 217nm, using a slit width of 1nm.
  2. Set up AAS with an air-acetylene flame, and lamp current 5mA.
  3. Measure the absorbance of 5 solutions
  4. Change the slit width to 0.5nm, reset peak meter needle to normal position.

Matrix effects

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