Boron forms refractory oxides, carbides, nitrides which can not be broken into atoms in a small residence time in Flame. So the analysis by AAS should be done in high residence time Graphite Furnace. But boron has a tendency to form refractory carbides on reaction with the surface of the graphite tube which decreases the life of the tube, decreases sensitivity of the analysis and will increase the memory effect. So the surface of the tube should be protected from reaction with boron of the analyte. This can be effected by addition of modifiers. Modifiers can act in two different ways. Either it will form a coating over graphite or it will react with boron before boron reacts with graphite furnace. We have used both the types of modifiers simultaneously to get better reproducibility. The modifiers used are Zirconium Nitrate and Nickel Nitrate.
a) Zirconium Nitrate forms very stable carbide on the surface of the graphite tube and reduces the B – C interaction [Zr – C bond strength is 561 kJ mole-1, whereas B – C bond strength is 448 kJ mole-1].
b) Boron is easily vaporized as Nickel Boride thus decreasing the tendency of Boron to react with Graphite tube surface.
Recovery Study with CRM Solutions was done and the results are tabulated below:
|Sl. No.||Conc. In StandardSolution used (mg/L)||Obtained conc. Afteranalysis in AAS/GF (mg/L)||% Recovery|
|1.||10.0||9.95 ± 0.05||99.5|
|2.||5.0||4.97 ± 0.04||99.4|
|3.||2.0||1.95 ± 0.05||97.5|
|4.||1.0||0.95 ± 0.05||95.0|
As the recovery is very good, the method was used for analysis of water samples and the values were compared with the values obtained by APHA 21st Edition method of Spectrophotometric method for determination of boron by Carminic acid – Conc. H2SO4. The results were found to be in conformity (Table below).
|Sl. No.||Conc. Obtained by Carminic Acid – Spectrophotometry (mg/L)||Conc. Obtained AAS / GF using modifiers (mg/L)||% Recovery|
|1.||3.42 ± 0.05||3.35 ± 0.05||97.95|
|2.||2.70 ± 0.03||2.65 ± 0.06||98.15|
|3.||1.92 ± 0.03||1.90 ± 0.04||98.96|
Introduction of the above method in the Analysis of Boron in Ferroalloys
The method was introduced in case of analysis of Ferro-alloys where boron is a tramp element and its presence is detrimental in some cases. But the problems in analysis boron in Ferro alloys are:
Dissolution of boron in Ferro alloys
Matrix effect due to presence of large quantity of other ions in the solution which have spectral interference.