Principles of UV/VIS spectroscopy (3) Applications

October 6, 2020

Color measurement

Fig. 7 shows an example of measuring three types of color filter mounted on an LCD panel. The transmission profiles for the red filter (600 nm or more), green filter (500 to 600 nm), and blue filter (400 to 500 nm) can be clearly distinguished.

Fig. 7 LCD color filter spectra

Quantitative determination of hexavalent chromium

The use of hexavalent chromium has been regulated by the EU RoHS directive. Hexavalent chromium has been widely used for plating and painting, but products must now be certified to be free of hexavalent chromium for RoHS compliance. The diphenylcarbazide reagent forms a complex with hexavalent chromium, producing a reddish-purple color (Fig. 8). The amount of hexavalent chromium present can therefore be quantified by placing samples such as electronic components in boiling water and coloring the eluate with diphenylcarbazide.

Fig. 8 Spectra obtained during elution and coloration of hexavalent chromium

SPF/PA test for sunscreen cream

Sunscreen creams block the UV rays that cause sunburn. They are categorized by their SPF value (effect at 280 to 320 nm) and PA value (effect at 320 to 400 nm). Until now, SPF/PA tests have required a healthy, non-hypersensitive group of subjects for skin patch testing, but such tests can now be performed using UV-vis spectroscopy (Fig. 9).

Fig. 9 Measurement of dedicated cell (top) and sun cream (bottom)