HOME  > Surface Finishing Tutorial  > #244 Absorption Photometry
Surface Finishing Tutorial

#244 Absorption Photometry

Category : Environmental conservation
June17, 2016

Although you can easily identify heavy metals using fluorescence X-ray, atomic absorption, and ICP emission spectrometric analyses, materials like cyanogen (CN-) and hexavalent chromium (Cr6+) require another analysis method. The method is called absorption photometry where you compare the color density of a substance against the object substance by coloring a pretreated sample with an indicator.

(1) Measurement principle

[Fig.1] shows the principle of density measurement by absorption photometry. This method is very similar to the colorimetric method where you compare a color against the standard color. Place a colored sample into the measurement cell as shown in [Fig.1] (a). Transmit the light from the light source through the filter to convert it into light in the specified wavelength (Io). During the transmission, part of the light will be absorbed. The transmitted light (It) is then converted into an electric signal by the photoelectric cell and displayed as transmittance or absorbance.

If you use a prism instead of a filter, the light wavelength can be selected from a wider range (spectroscopy). As shown in [Fig.1] (b), the maximum absorption wavelength can be found by measuring the absorbance while changing the wavelength for the colored sample. Use the light in this wavelength and measure absorbance of the standard solution whose concentration rate is already known. Then, prepare the standard curve graph (c) in order to predict the concentration of an unknown sample.

fig1

(2) Equipment overview

[Fig.2] shows the appearance of an absorptiometer.

fig2

(3) Characteristics

To determine how much hexavalent chromium is contained in a certain product, cut off a part of the product with a certain surface area and extract hexavalent chromium by pure water. Dilute or concentrate the extraction liquid to a proper concentration. Add the coloring indicator and measure absorbance to calculate the concentration of hexavalent chromium.

MISUMI USA eCatalog