Question

Standards Absorbance Ag (ppb) 0.00 0.000 0.013 0.076 0.162 0.245 0.405 0.598 0.748 2.00 10.0 20.0 30.0 50.0 75.0 100.0 Samples Absorbance 08002 08003 08004 08005 08006 08007 08008 08009 08010 0.079 0.058 0.129 0.082 0.797 0.063 0.009 0.028 0.136 Calculate the concentration of silver in each sample. Are there any problems? How will you address each of the identified problems?

the following samples were analyzed for silver. to each digestion flask 200 ml aliquots of ten different drinking water samples were added. silver was extracted by a co-precipitation procedure and collected by filtration. the precipitate was digested in 200 microliters hot concentrated nitric acid and diluted to 5 ml in a dilute phosphate solution. standards were prepared according to the following table. the samples were analyzed by graphite furnace AAS and compared to the calibration curve. results of the analyses follow: (chart in picture)

*** calculate the concentration of silver in each sample. are there any problems? how will you address each of the identified problems?

Answer 1

ans)

from above data that

The model:

PPB A y 0.0077x R2 0.9972 0 2 0.013 10 0.076 20 0.162 00.245 50 0.405 75 0.598 100 0.748 0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 冰) 20 40 60 80 100 120

A = 0.0077*C

or

C = A/0.0077

Then... substitute this equation for each sample:

NO	A	C
2	0.079	10.3
3	0.058	7.5
4	0.129	16.8
5	0.082	10.6
6	0.797	103.5
7	0.063	8.2
8	0.009	1.2
9	0.028	3.6
10	0.136	17.7

The only problem is that at high concentrations, such as ppm > 100 the model starts to fail, but this should not be of much attention since concentrations are not above 100 ppb