# Preparing gold nanoparticle dilutions for molar extinction coefficient estimation

You are now going to prepare a set of dilutions and use them to calculate the molar extinction coefficient of a gold nanoparticle solution.  Use the concentrations you calculated and recorded in Table 4 along with the absorbance values recorded on serial dilutions of gold nanoparticle preparations (see experimental data link).

Q30: Consider the 2:1 pH 5.4 gold nanoparticle preparation.  Given that the concentration of the stock solution is of the order of 3 x 10-9 M, how many milliliters of this solution will you have to pipette to prepare 5.00 mL of the following dilutions?

Nanoparticle concentration (M)

Milliliters of stock solution to pipette

0.00

5 x 10-11

1 x 10-10

2 x 10-10

4 x 10-10

8 x 10-10

1.5 x 10-9

3 x 10-9

Q31. What is the purpose of preparing a 0.00 M solution? How is it used in the analysis?

The following absorbance values were recorded when analyzing the eight solutions prepared above using the 2:1 pH 5.4 stock solution:

Nanoparticle concentration (M)

Absorbance

0.00

0

5 x 10-11

0.0501

1 x 10-10

0.0913

2 x 10-10

0.1778

4 x 10-10

0.3367

8 x 10-10

0.6364

1.5 x 10-9

1.172

3 x 10-9

2.622

Use Excel or equivalent software to plot the data above.

Q32. What relationship do you observe between the absorbance and concentration of nanoparticles?

Q33.  Do any of the data points deviate from the general behavior observed in the plot?

Q34. What parameter allows us to determine whether there is a good fit between absorbance and gold nanoparticle concentration?

Q35. What is the molar extinction coefficient for this specific gold nanoparticle preparation?  How does this value compare to the extinction coefficient reported in Table 1 for a gold nanoparticle of similar size?

Q36. How can you estimate the uncertainty on the molar extinction coefficient from the regression analysis?