Determination of Lead and Zinc Using Aas with Standard Additions

AIM:

To use atomic absorption spectrometry and a standard addition calibration to determine the concentration of lead and zinc in a solid bronze sample.

INTRODUCTION:

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 single physical parameter of the mixed analyte, establishing a relationship between additioin of the unknown with the change in physical parameter that allows an in-situ method of calibration.

RESULTS:

0.2ppm x 100 = 20mg.L-1
2 =
20mg.L-1 * 100/3   = 666mg.L-1

500ml (ie ½ L);

33.3mg/500ml = 0.333g/500ml

Real mass used = 0.3292g

Part A: External Standardisation

Zinc 10ppm from solution

V2 = C1V1/C2 = (100*100)/100 = 10ml

0.5ppm from 10ppm = 5ml

1ppm = 10ml

1.5ppm = 15ml

2ppm = 20ml

Lead 2.5ppm = 25ml



Figure 1: Concentration of Zinc in ppm and Absorbance using the GBC 901 AAS instrument

Concentration of Zinc (ppm) | Absorbance |
0 | -0.004 |
0.5 | 0.2873 |
1 | 0.5031 |
1.5 | 0.6427 |
2 | 0.7519 |
2.5 | 0.8247 |

Figure 2: Absorbance readings of unknown Zinc concentration and their mean, standard deviation, and standard error of their mean

Unknkown Absorbances (ppm) | Mean unknown absorbance (ppm) | Standard Deviation | Standard Error of Mean |
0.7992 | 0.801567 | 0.002122 | 0.001225 |
0.8033 | | | |
0.8022 | | | |

Figure 3: Absorbance with respect to concentration of zinc in ppm via external standardisation

Part B: Method of Standard Addition

Figure 4: Table of standard addition of...