Question

Analytical Chemistry - Determination of Fe in Vitamin tablet:

Iron was reduced by 25 mL 6M HCl and DI water.

Unknown Iron Sample: 10 mL diluted with DI water in 100 mL volumetric flask,

Iron Standards: 30 mL of 0.7385 mM

2 mL of hydroquinone solution, 3 mL o-phenanthroline solution and 10 mL of pH 3.5 buffer added to all flasks.

Blank (100 mL volumetric flasks)	flask 1	flask 2	flask 3	flask 4
0 mL Standard 50 mL DI Water	1 mL standard 10 mL Unknown	2 mL standard 10 mL Unknown	5 mL standard 10 mL Unknown	10 mL standard 10 mL Unknown

All flasks were diluted to the 100 mL mark. Spectroscopy was used to measure the absorbance at 510 nm and values of wavelength and absorbance for 6 runs are known.

Please explain in detail how to plot a Beer-lambert law from my wavelength and absorbance data in excel. How to plot the absorbance vs. iron concentration added in the standards (in μg) and calculate the μg of iron in the standards and determine the unknown concentration from the curve?

Answer 1

First input your data in the excel sheet like i have done.

then select these two column like this

Then click on the INSERT option and choose XY SCATTER ( I have set the arrow on the icon) . You will get your graph ready. Remember the quantity will you want to plot on the X axis should be in the first column(left) and the quantity for Y axis should be in the 2nd column(right).

Then for the graph between absorbance and concentconcentratioeat the above steps and you will get linear line. To add the trendline and slope. Double click on any plotted point on the graph and right click and then select ADD TRENDLINE. Their will be a list of options shown on the right , go down and click on the add equation and regression value options like as shown in the pictures.To calculate the unknown concentration with the help of graph. Plot the absorbance of unknown solution on the graph draw a line passing from that absorbance and make it intersect with the linear trend and the draw the line from that intersecting point towards the concentration axis and on which point it cuts the concentration axis that point gives is the unknown concentration.

The above graph is just to show the method and the readings are hypothetical.