1 What type of flames do you know Describe the differences b

1. What type of flames do you know? Describe the differences between them as related to (a) temperature achieved in the flame (b) interferences. 2. What are the main sources of matrix interferences in FAAS 3. Write the chemical reactions for (a) the interference of phosphates in FAAS determination of calcium in FAAS (b) the effect of EDTA as a releasing agent. 4. Can the \"standard addition\" method be used to minimize matrix effects?

Solution

1)

Different types of flames are

i) natural gas-air-------------------- 1700-1900^oC

ii) hydrogen-air----------------------- 2000-2100^oC

iii) acetylene-air---------------------- 2100-2400^oC

iv) acetylene-nitrous oxide------- 2600-2800^oC

v) acetylene-oxygen---------------- 3050-3150^oC

The formation of ground state atoms can be inhibited by two general forms of chemical interferences

i) Incomplete dissociation of compounds----most common

ii) Ionization----occurs at high temperature flames like acetylene-nitrous oxide

2)

When a sample is more viscous or has different surface tension than the standard it can result in difference in sample uptake rate due to changes in nebulization efficiency. This is one of the matrix interference.

Inaccurate results are also caused due to precipitation of the concerned sample like hydrolysis of silicon and tin.

Continous aspiration of sea water may result in the build up of solid deposits in the burner head which partially obstructs the flame lowering the absorbance.

3)

Ca²⁺ + PO₄^3--> Ca₃(PO₄)₂

Ca²⁺ + EDTA -> Ca[EDTA]^2-

EDTA acts as a protective agent,forming a stable but volatile complex with calcium.