To use atomic absorption spectrometry and a standard addition calibration to determine the concentration of lead and zinc in a solid bronze sample.
Atomic Absorption Spectroscopy is generally performed with external standardisation using a calibration curve of known concentration standards and using the equation of the linear trendline to determine the concentration of the unknown by rearranging the linear equation. However, the efficienchy of this method is reduced and can be afflicted with errors by the presence of other components in the experimental sample. These matrix interferences are overcome using the standard-addition method by measuring and varying a ...view middle of the document...
0 | 0.2171 |
5 | 0.4308 |
10 | 0.6075 |
15 | 0.7495 |
20 | 0.8436 |
Figure 5: Absorbance with respect to addition of unknown lead sample (ml) to 25ml of known lead standard
Figure 6: Table of [Pb](ppm) and absorbances recorded
[Pb](ppm) | Absorbance |
0 | 0.0004 |
0.5 | 0.2645 |
1 | 0.4871 |
1.5 | 0.6692 |
2 | 0.7887 |
2.5 | 0.884 |
Figure 7: Absorbance readings of unknown Lead concentration and their mean, standard deviation, and standard error of their mean
Unknown Absorbances (ppm) | Mean unknown absorbance (ppm) | Standard Deviation | Standard Error of Mean |
0.6703 | 0.674167 | 0.006018 | 0.003474 |
0.6711 | | | |
0.6811 | | | |
Figure 8: Absorbance with respect to concentration (ppm) of lead
The AAS was used to create a Zn calibration curve, and then the unknown sample was measured three times for accuracy. The absorbances may be averaged to determine the mean absorbance.
Excel may determine the standard deviation of the absorbances, which is used to calculate the standard error of the mean.
The mean absorbance may be substituted into the equation of the line in order to determine the concentration of the unknown.
Figure 9: Concentration readings and mean concentration of the unknown zinc sample
Unknown Concentration Readings (ppm) | Mean unknown concentration (ppm) |
2.267 | 2.281 |
2.291 | |
2.285 | |
The Pb sample may similarly be averaged to determine the mean absorbance.
(0.6703+0.6711+0.6811)/3 = 0.67416