Atomic Spectroscopy

Background

Atomic Spectroscopy is based upon the ability of atoms to absorb or emit light. In atomic absorption spectrophotometry (see graph at right), the atoms are heated enough in a flame or graphite tube to free them from solvents and disrupt the formation of salts, but not enough to pump electrons to an excited electronic state. The free atoms, with electrons in the ground state, are ready to absorb light of just the right energy to promote electrons to an excited electronic state. The greater the concentration of that atom in the sample, the less light reaches the detector; so it is relatively straightforward to determine concentration of a particular atom in a sample by measuring how much light it absorbs. 

In atomic emission spectrophotometry (see graph at right), the purpose of heating the sample is not only to free the atoms from the solvent and formation of salts, but to provide enough energy to pump electrons into excited electronic energy levels. As these electrons fall back to lower energy levels, they emit light at specific wavelengths. The more light that is detected at that wavelength, the more of that element must be in the sample. Instrumentation to carry out atomic emission would not need a lamp. Inductively coupled plasmas exist at extremely high temperatures (around the temperature of the surface of the sun), and are used in atomic emission spectroscopy.

This Atomic Spectrophotometer operates in both atomic absorption and emission modes. The FS in the name stands for Fast Scanning, which means that this instrument can take a measurement for one element, then quickly scan to the next wavelength to collect a measurement for another element, then the next, etc. This means that the instrument can collect data on approximately ten elements in the same time that it would take to measure one element. It has 4 lamp sockets, and can automatically switch between these four lamps using a moveable mirror. Automation of the mirror position, monochromator wavelength, and data collection are can be fully automated.

Perkin Elmer 3110 Atomic Spectrometer

The PE 3110 is a stand-alone AA that is not interfaced to a PC. The instrument's straight-forward design and rock-solid optical bench leads to stable, reproducible results, and provides a great tool for learning this technique. This spectrometer is in excellent working condition and provides us with flexibility when several groups of students are working on AA at the same time.