Evaluation of UV-Blocking &Tints in Sunglasses by

Scanning VIS-Spectrophotometry

 

INTRODUCTION:

There are many wavelengths of Energy in the Electromagnetic Spectrum. In the middle, is a spectral region of Light called the UV-VIS (Ultra-Violet/Visible) Spectrum. These wavelengths of energy, from 190nm. beginning in the UV, through 900nm. at the end of the VIS, can generate a tremendous amount of descriptive information about molecules that absorb certain portions of this Spectrum. For example, materials that ABSORB the energy below 325nm. are UV-Blockers. Such materials are used in Sunscreen products to protect the skin from exposure to potentially damaging Ultra-Violet radiation from the Sun. Using a Scanning UV-VIS Spectrophotometer and by running solutions of Sunscreen lotions with varying SPF (sun protection factors), the Absorbance Peaks of the UV-Blockers can be easily seen. By "calibrating" the Spectrophotometer with Standard solutions of Known SPF values, an Unknown Sample can be scanned and the SPF calculated by comparing its Absorbance Peak to that of the Standard.This is the heart of quantitative analytical spectroscopy; one of the most popular analytical methods used.

 

PURPOSE:

To prepare a "Calibration Curve" of UV Absorbance values vs. SPF Factor using Known Standard SPF Solutions in i-Propyl Alcohol (IPA); and to evaluate an Unknown Sunscreen solution to determine its SPF factor. Most UV-Blocking materials have Peaks at 292nm. and/or 309nnm., depending on the exact chemical or mixtures used to block the various wavelengths of the Sun's UV light.

 

 

 

INSTRUMENTS NEEDED:

 

· 6405 UV-VIS Spectrophotometer

(from Edu-Chem Innovations) INFO/Buy IT!

 

· 10mm. square QUARTZ Cuvettes (must be TRANSPARENT in the UV region)

 

 

 

 

SUPPLIES:

  1. Disposable plastic pipets/eyedroppers
  2. Text Box: FUN-SCI Kit Includes all supplies INFO/Buy IT! Vials of Standard Sunscreens w/ SPF-4, SPF-15 and SPF-45 values; solutions in IPA. These are prepared by measuring 0.025 grams / 100ml. IPA; and have been prepared for you due to the very low weight of material used for these tests
  3. Pure IPA (for "BLANK"/Zero readings)
  4. Wash-bottles of IPA and DI Water (for rinsing out cuvettes)

 

SAMPLES:

 

Vials of Unknown SPF Sunscreen solutions in IPA; from SPF-0 to SPF- 60. These are prepared by measuring 0.025 grams/100ml. IPA; and have been prepared for you due to the very low weight of material used for these tests

 

 

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