Qualitative and Quantitative Analysis of Food Dyes >> Step 3 : Part 2

Qualitative and Quantitative Analysis of Food Dyes

Step 3 - Part 2: Measuring the absorbance of the standard solutions


Measuring the Absorbance :
Now that we have created a set of diluted solutions, we can take the absorbance of each solution and construct a Beer's Law plot. The absorbance is measured at the analytical wavelength, the wavelength for which the absorbance is highest. Recall that the highest peak in the spectrum for Blue #1 was at 620mn. Thus, the analytical wavelength for Blue #1 is at 620nm.

The following interactive simulation measures the absorbance data for the standard solutions of Blue #1 and Red #40. Drag a vial of dye solution onto the spectrophotometer to see its absorption spectra and absorbance at the analytical wavelength. Use this data and the blank graph to create a calibration plot for Blue #1.

Plot the Absorbance versus Concentration (expressed as dilutions) for the blank and the 5 diluted Blue #1 samples. Label the axis and title the graph; then draw a best-fit straight line through the points. (You may also use Microsoft excel to create your graph). You will use this information in the next set to determine the concentration of dye in drink.

Download the blank graph for Blue #1, with a table of absorbance data. This does not need to be turned in to your TA.

Now that we have obtained a calibration plot of absorbance versus concentration at the analytical wavelength for blue #1, we can use this plot in the next step to determine the concentration of the dye in our drink.