Sunscreen Student Procedure
Part I. Determination of Ultraviolet Spectra of Sunscreen Active Ingredients 1. Clean the quartz cells by rinsing them with isopropanol (IPA). 2. Fill both cells with IPA and dry the outsides with a Kimwipe. 3. Place the cells in the reference and sample cell holders within the spectrometer with the clear sides of each cell facing the open slots of the cell holder. 4. Click the grey start button on the computer monitor. 5. When the dialog box comes up for the blank, click OK. A background correction is carried out from the maximum to the minimum wavelength range (500 nm 200 nm). 6. Take out the sample cell (front cell) and place its contents into the organic waste beaker. 7. Using the transfer pipette take the Avobenzone spectral solution and transfer it into the sample cell until approximately ¾ full. Place the sample cell back into the spectrometer and click OK to record the Avobenzone spectrum.
Part I. Determination of Ultraviolet Spectra of Sunscreen Active Ingredients- cont. 8. Repeat the process for the next three sunscreen spectral solutions, (oxybenzone, octocrylene, and octisalate) rinsing the sample cell with IPA and wiping the exterior surfaces of the cell with a Kimwipe before filling the next sample solution. 9. Evaluate each spectrum for the wavelengths where the greatest absorbance occurs (UV max ), the absorbance (A) at UV max and classify each sunscreen molecule as sunscreen for UVA, UVB or both. 10. Record your results in Table 1.
Part II. UV Absorbing Bead Experiments 1. Place one bead in the bottom of five plastic UV cells. Mark each cell with the cell number given in Table 2 on worksheet. 2. Using a plastic pipette, transfer 1 ml of each sunscreen stock solution into the previously marked cell. The first mark on the pipette corresponds to 1 ml. 3. Prepare a control by adding 1 ml of isopropanol to cell 5 (contains no sunscreen molecules). 4. Place all the cells onto cell holder at marked positions 1 5 and carefully place the holder into the UV box at the front position (long wavelength, UVA). Press the white button on top. 5. Using a timer, expose each cell to the light for 2 minutes. 6. Turn off the UV light, carefully remove the cell holder and observe the beads. 7. Quickly evaluate the darkness of each bead in each sunscreen solution by comparing to the control (cell 5). Use a scale of 0 5 to estimate the color intensity of each solution and assume the color intensity of the control is equal to 5 (dark purple) and a value of 0 for no color change. Perform the evaluation quickly as the color intensity diminishes rapidly. 8. Repeat this procedure, steps 3 6, for short wavelength UV light (UVB). 9. Rate each sunscreen s strength for its UVA or UVB activity as weak (color intensity = 4, 5), medium (2, 3) or strong (0, 1) protection.
Part III Preparation and Evaluation of a Sunscreen Formulation Decide on the selection of two ingredients for their formulation. Each formulation will be compared against commercial sunscreens. Formulation Preparation 1. Mark 6 UV cells at top of each with numbers given in Table 4 below. Place a UV absorbing bead into each cell. 2. Select your two ingredients from the 1.5 mg/ml sunscreen stock solutions. Pipette 2 ml of each solution into a vial and mix. The top mark of the pipette corresponds to 2 ml. 3. Pipette 1 ml of your formulation into a UV cell containing a bead. The bottom mark on the pipette corresponds to 1 ml. 4. Transfer 1 ml of isopropanol into cell 2. This sample is the control for your formulation. 5. Place the control and formulation samples onto the cell holder at positions 1 and 2 and set cell holder aside.
Part III Preparation and Evaluation of a Sunscreen Formulation- cont. Commercial Sunscreens 1. With a Q-tip, squeeze a dab of SPF 15 sunscreen cream and carefully spread the cream over three faces of the cell 3 and its bottom. One clear face of the cell should have no cream applied. Ensure that the cream is evenly spread in a thin layer over the faces. This procedure should mimic the coverage of human skin. 2. Place a cover on the top of the cell and place the cell at position 3 of the cell holder with the uncoated surface facedown. 3. Repeat steps 1 and 2 for the remaining sunscreens, SPF 30 and 50. Place these cells at positions 4 and 5. 4. Place a cover on cell 6 (no coating) and place it onto position 6 of the cell holder with one of the clear faces facing up.
Part III Preparation and Evaluation of a Sunscreen Formulation- cont. Evaluation: 1. Carefully, place the cell holder in the center of the UV box. 2. Turn on both short and long wave lamps and expose samples for 2 minutes. 3. Carefully remove the cell holder from the UV box and place it on the bench. 4. Quickly evaluate your sunscreen formulation (cell 1) against its control (cell 2) based upon the 0 5 color intensity scale and record your results in Table 3. 5. Repeat the evaluation for the commercial sunscreens (cells 3, 4, 5) against their control (cell 6) using the same 0 5 color intensity scale. Record your results in Table 3.
Part III Preparation and Evaluation of a Sunscreen Formulation- cont. Ultraviolet Spectrum of Formulation 1. Transfer 1 ml of your formulation into a 50 ml volumetric flask. 2. Add isopropanol to the flask up to the mark at neck of the flask and place the cap on the flask. 3. Holding the flask in the palm of your hand with your thumb on the cap, mix by inverting the flask 5 times. 4. Clean the sample and reference quartz UV cells with isopropanol. 5. Fill the sample and reference cells with isopropanol to about ¾ of the cell volume. Dry the outside surfaces of the cells with a Kimwipe. 6. Place the cells into the UV spectrometer and obtain a blank reading from 500 to 200 nm. 7. Empty the sample cell and with a pipette transfer a portion of your formulation to about ¾ of the cell volume. 8. Place the sample cell into the spectrometer. Scan the sample and print a spectrum.