Whilst atomic absorption spectroscopy (AAS) is a robust technique in the field of elemental analysis, the technique can suffer from a variety of interferences from physical, chemical, and spectral phenomena. In this TechTip we will look at what steps can be taken to reduce chemical interferences to improve the quality of your analytical data.
As the name suggests, these interferences come from when the chemistry of elements and compounds become a problem during analysis, lowering the number of atoms in the free state which will reduce the overall absorbance signal.
1. Refractory compounds
A classic example is the formation of phosphate, sulphate, or aluminate species, known as refractory compounds. These anions, if present in the sample matrix bind with target analytes such as calcium and magnesium to form compounds that cannot be dissociated as easily by the flame’s thermal energy, leading to false low readings.
The addition of a releasing agent, which is a compound that reacts preferentially with interfering ions “stealing” the interference away from the target analyte. A common releasing agent is lanthanum chloride, seen in Figure 1 below, which will free atoms up allowing greater absorbance and improving overall analysis.
2. Ionisation interferences
When the flame becomes too hot (especially in nitrous oxide/acetylene flame), easily ionisable elements such as sodium, potassium and calcium can lose electrons and become ions. Unfortunately, these ions absorb at a different wavelength than the neutral atom, therefore becoming “invisible” to the detector and therefore a lower-than-expected absorbance will be measured. signal.
To overcome this, you can add an ionisation suppressor which will stop target atoms from losing electrons by flooding the flame with electrons, shifting equilibrium to produce more free atoms of the target analyte (see equations below). A Common suppressor used is caesium chloride, this must be added to all samples, standards, and blanks to ensure matrix matching, which aids in effective analysis.
To learn more about AAS and the interferences associated with the technique join our:
