Spectrophotometer

Evaluation of results against a commercial spectrophotometer

Aim
The aim of this part of the laboratory is to check the accuracy of results produced by the custom device developed during the previous sessions against a commercial spectrophotometer (Model: Novaspec 4049).

Method guidelines
1. Turn the Novaspec 4049 spectrophtometer ON using the switch at the back of the device.

2. A ‘CAL’ sign will appear on the left hand side screen. Wait until the calibration is complete.

3. When the device is ready, adjust the wavelength selection by pressing the ‘+’ and
‘-‘ buttons. Set this to 600 nm.

4. Select the %T ordinate mode.

5. Insert the cuvette containing water into the sample compartment. To do this, lift the lid of the sample compartment and then insert the cuvette into the inlet. Once inside, close the lid to prevent interference from ambient light.

6. Press the ‘Set Ref’ button. This should reset the displayed reading to • Once reset, remove the water- containing cuvette from the sample compartment.

7. Then, place into the sample compartment the cuvette containing solution A. Record the displayed reading.

8. Repeat step 7 for solutions B, C and D.

9. Adjust the wavelength selection to 510 nm.

10. Repeat steps 4-8.

11. Calculate the extinction coefficient for solutions A (CrNO3) and B (CoNO3) at 600 nm and at 510 nm. Complete the following table:

12. Calculate the concentrations of CrNO3 and CoNO3 in solutions C and D. Complete the following table:

CrNO3 in (C) CoNO3 in (C)
[CrNO 3] C = M [CoNO 3] C = M
CrNO3 in (D) CoNO3 in (D)
[CrNO 3] D = M [CoNO 3] D= M

13. Calculate the percentage error in the extinction coefficient and concentration values found using your device against those obtained using the commercial spectrophotometer.
     M1: measurements from your device.
     M2: measurements from spectrophotometer.

14. Show all your workings in your final report

15. If you have time, reduce errors by making improvements to your system, and/or if available, try to connect your spectrophotometer to a data acquisition card and start experimenting with a basic data acquisition VI in Lab VIEW.