Experiment on Sunscreens - Report Example

Name: Lab Instructor: Date: Research Experiment on Sunscreens Objective The objectives of this experiment were to: i. Compare the absorbance of prepared Zinc oxide nanocrystal with different concentrations with sunscreens of SPF 50+ from different companies. ii. Compare sunscreens with the same SPF rating from the same company. iii. How the active ingredients and preservatives may affect sunscreen absorbance. Introduction Sunscreens are available from different producers and are of different types with varying levels of skin protection. The sun protection factor (SPF) is the most commonly used measure of protection from ultraviolet light. It refers to the ability of the sunscreen lotion to block UVB and UVB rays from the sun and describes the amount of time a sunscreen user can stay in the sun before the skin stars to burn (Gause and Chauhan). The sunburns which are caused by the ultraviolet rays are linked to skin damage. The SPF rating is simply a measure of the time it would take for your skin to experience sunburn without a sunscreen, as opposed to the time it would take with a sunscreen on the skin. For example, an SPF rated 50 means that one can stay out in the sun 50 times longer after applying the sunscreen as opposed to when the sunscreen is not applied before noticing sun skin burns. Both UVA and UVB rays contribute to the high risk of skin cancer (Slevin). There are two types of ingredients used in sunscreens; Inorganic and organic ingredients. Zinc oxide is an example of inorganic ingredient used in sunscreens as one of the active ingredients. It works by making the sunscreen opaque, and thus, light passing through the sunscreen is reflected and scattered in what is referred to as physical blocking. It is commonly used in high SPF sunscreens. Octyl methoycinnamate, 4-t-butyl-4-methoxydibenzoylmetane and 4-methylbenzylidene-camphor are some of the chemical ingredients used in sunscreens and are sensitive to solvent properties. When the UVA light is irradiated on these substances, they break down and become degraded or transfer energy to other biological targets. In this experiment, a study was done to investigate the UV absorbing characteristics of ZnO nanoparticles. The research also involved a study and comparison of different sunscreens with an SPF rating of 50 from the same company, and also from different companies. In addition, the experiment examined the effect of active ingredients and preservatives used on absorbance of the sunscreens. Procedure Preparation of ZnO nanocrystals: Zinc oxide nanocrystals were prepared by reacting zinc acetate dehydrate (Zn(C2H3O2)2∙2H2O) with tetramethyl ammonium hydroxide pentahydrate (N(CH4)4OH·5H2O). About 0.015 g of zinc acetate dehydrate was weighed and dissolved in 7 mL of ethanol. A solution of tetramethyl ammonium hydroxide was then prepared by dissolving 0.035 g of tetramethyl ammonium hydroxide pentahydrate in 7 mL of ethanol. Finally, 0.2 mL of the tetramethyl ammonium  hydroxide  solution was measured and then added to a fused silica cuvette with 2 mL of ethanol and 0.5 mL of the  zinc acetate solution. Preparation of Standard solutions: The standard solutions of 4-t-butyl-4-methoxydibenzoylmetane, octyl methoycinnamate and 4-methylbenzylidene-camphor with concentrations of 0.5mg/mL were prepared in 2-propanol, then diluted about 100X and their absorption spectra observed. A picture taken during the experiment for preparation of the standard solutions Results ZnO nanoparticles The absorbance of ZnO prepared in the procedure above was tested. The spectrum below shows the characteristic absorbance of the sunscreen ingredient. Figure 1: Absorbance spectra for ZnO The spectrum shows that ZnO has a strong absorbsorbance of ultraviolet light at a wavelength range of 250-350 nm, which makes it a suitable ingredient for use in sunscreens to protect the screen against UVB rays. Sunscreens with ZnO as one of its ingredients are usually opaque in the visible light and can protect the user from UVB rays (Lowe). Addition of 0.5 mL ethanol dissolves the ZnO solution, thus, making it less concentrated. This reduces the capacity of the ZnO to absorb UV light, hence, the trend line for the dissolved ZnO is lower. The standard solutions In figure 2, the spectra for prepared standard solutions of 4-t-butyl-4-methoxydibenzoylmetane, octyl methoycinnamate and 4-methylbenzylidene-camphor are shown. 2-propanol provides a solvent for the three solutions. It dissolved the ingredients completely. Of these three ingredients (with the same concentration of 0.5 mg/L) tested, 4-methylbenzylidene-camphor proved to be the best ingredient to absorb UV radiation at a wavelength range of approximately 300 nm, which falls in the UVB region. Octyl methoycinnamate was the second highest followed by 4-t-butyl-4-methoxydibenzoylmetane. All the ingredients absorb UVB at a wavelength range of 280-320 nm, which makes them suitable ingredients for protection from ultraviolet light in the UVB region. This result shows that the type of ingredients used in sunscreens affect the UV absorbance of the product. Figure 2: Absorbance spectra for the standard solutions Comparison of sunscreens with SPF of 50 from the same company Figure 3: Different Sun Sense sunscreens rated SPF 50 Figure 4: Error-Sun sense-Anti-ageing face In the figure 2 above, the absorbance of four sunscreens from Sun Sense with an SPF rating of 50 is shown. Although the sunscreens have the same SPF, they display different UV light absorbing capabilities. It is evident from the absorbance spectra in figure 3 that he Moisturizing face has the highest absorbance, followed by Anti-ageing face and Sensitive respectively. Sunscreens with a high rate of SPF offer more protection to the harmful ultraviolet radiation from the sun, which is linked to majority of skin cancers (Reyes and Rodríguez). A sunscreen with an SPF of above 50 is approximated to block 98% of UVB rays (British Medical Association). The Sensitive sunscreen lotion provides the highest UV protection compared to the other three sunscreens, closely followed by the tow Anti-ageing lotions. Sun Sense sunscreens contain the ingredients and preservatives as shown below: The difference in the UV light absorbance capabilities is due to the different active ingredients as well as preservatives used in the sunscreens and their concentrations. In figure 4 below, absorbance of four different sunscreens with an SPF rating of 50 from Hamilton Company is shown. Hamilton sensitive shows the highest UV absorbance, followed by Hamilton toddler and Hamilton active family respectively. Hamilton everyday face shows the lowest absorbance. This is because the sunscreen did not dissolve in water. The absorption wavelength lies between 280 and 320 nm, which make these ingredients suitable for UVB protection (Slevin). Figure 5: Different Hamilton sunscreens rated SPF 50 Below are the active ingredients used in the manufacture of Hamilton sunscreen lotions. Sunscreen Active ingredient Preservative Hamilton - Active family Octyl Salicylate 5% Homosalate 10% Butyl Methoxydibenzolylmethane 4%, Octocrylene 8%. Phenoxyethanol,Benzyl Alcohol, Hydroxybenzoates. Hamilton - sensitive 4-Methylbenzylidene Camphor 4% OctylTriazone 3%, Butyl-t-methoxydibenzoylemthane 4% Octocylene 4% Phenoxyethanol, Benzyl, Alcohol, Hydroxybenzoates Hamilton - toddler 4-Methylbenzylidene Camphor 4%, Camphor 4% octylTriazone 3% Butytmethoxydibenzoylemthane 4%, Octocrylene 4%. Phenoxyethanol, Benzyl, Alcohol, Hydroxybenzoates Hamilton - Everyday face Octocrylene 3%, Butyl Methoxydibenzolylmethane 3%, 4-Methylbenzylidene Camphor 2%, OctylTriazone 3% Phenoxyethanol, Hydroxybenzoates Again, the type of active ingredients and their concentrations vary from lotion to lotion, even though they have the same SPF rating. Out of the four sunscreens, Hamilton toddler proved to have a slightly higher UV absorbing capability compared to the rest, closely followed by Hamilton sensitive and Hamilton active family respectively. Hamilton everyday face shows the lowest UV absorbing capability of the four sunscreens. Both Hamilton toddler and Hamilton sensitive contain 4% of 4-Methylbenzylidene Camphor as an active ingredient. This ingredient has relatively good UV absorbance characteristics as seen in the results reported in figure 2. The following figure shows the UV spectra obtained when three different sunscreen lotions with an SPF rating of 50 from Cancer Australia were tested for their absorbance. Figure 6: Absorption spectra for different sunscreens from Cancer Australia All the three sunscreens show the same characteristic absorbance with slight variations in absorbance. The absorbance wavelength is between 250 and 300 nm, which means that the screens protect the skin from ultraviolet rays in the UVB region (Reyes and Rodríguez). The Active dry touch lotion shows slightly better UVB absorbing capability compared to the rest of the sunscreens, followed by kids sunscreen and sport respectively. Below are the active ingredients in each of the sunscreens, and their proportions. Figure 7: Error-Cancer Council Active-dry touch sunscreen When different sunscreens from different companies but all with the same SPF rating of 50 were tested for their absorbance. Figure 8: Absorbance spectra for four different sunscreens from four different companies, all rated SPF 50 All the four sunscreens show different absorption characteristics, with Neutrogena and Nivea emerging as the better UV absorbers compared to the other two sunscreens. Neutrogena shows the highest UV absorbance of the four sunscreens. ProPaira and Le Tan show lower UVB absorbance capabilities. Le Tan shows the lowest UV absorbance. Figure 9: Absorbance of sunscreens from Sun sense with an SPF rating of 50 From figure 9 above, all the sunscreens tested show relatively varying absorbance characteristics. However, the Neutrogena-Dry touch sunscreen lotion can be observed to have a slightly higher UV absorbance compared to the rest of the sunscreens. It is followed by Sun sense-Sensitive, Sun sense-moisturizing face and Sun sense Anti-ageing face respectively. Conclusion This research experiment provides a valuable knowledge in the preparation of sunscreens and how the ingredients and preservatives used affect the absorbing characteristics of the resulting sunscreen. All the objectives of the experiment have been successfully achieved. In our tests, the sunscreens labeled with the same SPF 50 were found to have different UV absorbing characteristics depending on the type of ingredients used, and their proportions. ZnO, which is an inorganic ingredient, has a lower UV radiation absorbance compared to organic active ingredients. Analysis of Results Question 2. The peak of ZnO is at a wavelength 295 nm. Question 3. Nanoparticles of ZnO physically block the penetration of UV light by reflection and scattering, thus, they are opaque and do not allow UV light to pass through. Question 5. Inorganic components of sunscreen, specifically ZnO and TiO2 are not soluble in isopropanol, but form dispersions. Question 9. Each natural compound in a sunscreen has its unique characteristic light spectrum, and therefore, by observing the spectra of unknown compounds and comparing with the spectrum of a known compound, the unknown compound can be identified. Question 10. The spectrum for ZnO is wider in the wavelength range of 280-320 nm compared to the spectra of the other sunscreens. The sunscreen that contains ZnO as an active ingredient is Sun sense – sensitive. Question 11 The Sun- sense sensitive lotion contain mainly titanium dioxide and zinc oxide as inorganic ingredients, while all the others contain organic ingredients such as Bemotrizinol, Methoxycinnamate, DiethylaminoHydroxybenzoyl hexyl benzoate, Methylenbis-benzotriazolyltetramethylbutylphenol, octyl salicylate, Homosalate, Butyl Methoxydibenzolylmethane, Octocylene, 4-Methylbenzylidene Camphor, OctylTriazone, Butyl-t-methoxydibenzoylemthane etc. The high SPF is due to good UV absorbance capability of the ingredients used. Their concentration in a given sunscreen is limited to certain levels because they are toxic at high concentrations. References Read More