Analysis of Aluminium - Analytical Chemistry

Analysis of Aluminium in Potable waters by Atomic Absorption Spectrophotometric Techniques

Objectives

1. To introduce the basic principles of Atomic Absorption analysis.
2. To Optimise the furnace temperature programme conditions for the analysis of Aluminium.
3. To determine the optimum conditions for the analysis of Aluminium by flame atomisation and to carry out the analysis using two seperate readouts on flame AAS instrument.

Part A:
Non-Flame Atomic Absorption – Electrothermal Atomisation/Graphite Furnace Atomic Absorption Spectrometer (GF-AAS)

Introduction

Atomic Absorption relies on the principle that each atom absorbs light of a particular wavelength, and hence at that wavelength the quantity of that absorption is proportional to the elements concentration. The first technique used in this analysis was Electrothermal Atomisation, known as Graphite Furnace-AAS. The components of a Graphite Furnace AAS are similar to that of Flame AAS, they more or less use the same components, with the exception of the component used to heat the sample.

For a Graphite Furnace Atomic Absorption Spectrometer the schematic is:
Hollow Cathode Lamp → Graphite Tube → Monochromator → Detector

The Hollow Cathode Lamp (HCL) is a selective/specific light source made from the element of interest. The HCL contains an inert gas which is usually Argon or Neon. Ionization of the inert gas takes place, which causes acceleration of the gas into the Cathode. This causes the metal atoms (Al) of the cathode to sputter into the gas phase. The collision of sputtered atoms with the Argon atoms or electrons, excite the metal to higher energy levels. It is the process of decay that occurs which causes excited electrons to emit light in their return down to lower energy levels which is shone through the sample in the Graphite tube.

Ar + e- → Ar+ = 2e-
M(s) + Ar+ → M(g) + Ar
M(g) + Ar+ → M*(g) + Ar
M*(g) → M(g) + hv (light)

The monochromator