Origin of Spectral Interference

As the emission lines of hollow cathode lamps are very narrow, interference due to overlapping lines is rather unlikely. The separation between two spectral lines would have to be less than typically 0.01 nm for such an interference to occur. As an example, the vanadium absorption line at 308.211 nm interferes in the anal- 

Spectral interferences may also result from combustion products that exhibit broad-band absorption or particulate matter that causes scattering of the incident radiation. As both reduce the spectral radiance of the Hght source, they may erroneously lead to an overestimation of the absorbance and, consequently, the concentration. When the combustion or the particulate products arise from the fuel and oxidant mixture, they may be determined by measuring the absorbance while a blank is aspirated into the flame. The situation is more compHcated if the absorption or scattering arises from a product associated with the sample or its matrix. 

For example an elemental absorption line can be interfered by a molecular absorption line from reaction products of co-existing elements in the sample. In the case of Ba determination in the presence of Ca the elemental absorption line at 553.6 nm can be overlapped by a broad CaOH absorption band in the range 548.0 nm to 558.0 nm. In many cases such interference can be ehminated by replacing air as oxidant by nitrous oxide. The resulting higher flame temperature leads to the decomposition of the CaOH and ehmiriates the absorption band. 

While electrothermal AA was considered to be more susceptible than flame AA to the interferences discussed above, this appears no longer to true with the instrumental developments that have been realised over the past decades. Nowadays, graphite furnace AA may be considered as being affected by interferences to a level not higher than observed with flame AA. 

---

This chapter will describe the operation of an ICP and explain why certain physical parameters contribute to sensitivity and freedom from interferences. Commercially available, modular assembled (ICP-AES) systems will be discussed with respect to the general configurations which they employ. The origin of spectral interferences and their accomodation will be explained. The effect of operating parameters and data-processing requirements will be discussed. General as well as environmental applications will be enumerated and specific examples given. 

---