Part B: Calibration

Question

The extract must fall into a specified range to provide a reading with the spectrophotometer. A sample that is too concentrated will not provide a valid measurement. To assure the sample falls within a readable concentration range, follow the steps provided.
Materials:
Two 3 mL syringes
Ethanol
Plant extract from Part A
2 cuvettes
Kimwipes
Sharpie marker
Small test tube rack
Genesys 20 Spectrophotometer
Procedure:
1. Set the spectrophotometer wavelength to 640 nm.
2. Push the A/T/C button to select % transmittance. The digital readout will show %T.
3. Label one of the 3 mL syringes ethanol. Label the second syringe leaf extract.
4. Dispense 3 mL of ethanol into a clean glass cuvette. (Wipe off finger prints with a Kimwipe.) Important: This cuvette is a “blank” that will be used throughout this lab to calibrate the spectrophometer.
5. Insert the blank in the cell holder and close the door.
6. Press the 0 ABS/100%T key to set the blank to 100% transmittance.
7. The blank provides a standard for reading. Remove the blank and proceed with testing the extract by following the same procedure.
8. Dispense 3 mL of the extract into a clean glass cuvette. (Wipe off all fingerprints with a Kimwipe.)
9. Insert the cuvette in the cell holder and close the door.
10. A reading of 30%-40% transmittance is best. If %T is greater than 40%, you may skip the dilution step. If it shows less than 30% transmittance, dilution of the sample is required.
11. To dilute the filtered extract, add 0.5 mL of ethanol (using the clean ethanol syringe). Tightly hold a finger over the cuvette and invert to mix. Re-test the percent transmittance. Continue with 0.5 mL increments of ethanol until the reading is greater than 30% transmittance.
use the above information and write a good procedure in a practical correctly in a sentence form.

Answer 1

Calibration Procedure for Spectrophotometric Analysis of Plant Extract

1. Begin by setting the spectrophotometer to a wavelength of 640 nm and select the % transmittance mode by pressing the A/T/C button, which will display the %T on the digital readout.
2. Label one 3 mL syringe as "ethanol" and the other as "leaf extract."
3. To prepare a blank sample, dispense 3 mL of ethanol into a clean glass cuvette, ensuring that any fingerprints are removed using a Kimwipe.
4. Place the cuvette containing the ethanol blank into the spectrophotometer's cell holder and close the door securely.
5. Press the 0 ABS/100%T key to calibrate the instrument, setting the blank to 100% transmittance.
6. Remove the ethanol blank cuvette and prepare to test the plant extract. Dispense 3 mL of the filtered plant extract into a clean glass cuvette, again wiping off any fingerprints.
7. Insert the cuvette filled with the plant extract into the spectrophotometer cell holder and close the door.
8. Monitor the % transmittance reading on the display; aim for a reading between 30% and 40%. If the reading exceeds 40%, no dilution is necessary and you may proceed to further analyses. Conversely, if the reading is below 30%, dilution will be required.
9. To dilute the extract, use the ethanol syringe to add 0.5 mL of ethanol to the cuvette. Seal the cuvette with your finger and gently invert it to mix the contents thoroughly.
10. Re-insert the cuvette into the spectrophotometer and check the % transmittance reading. Continue to add 0.5 mL increments of ethanol, mixing thoroughly each time, until the % transmittance exceeds 30%, ensuring that you maintain a valid range for accurate measurements.