Photometry

From Saltwiki

Author: Hans-Jürgen Schwarz, NN
English Translation by Sandra Leithäuser
back to Analysis of Salts

Abstract

The basic principle of photometry is to produce a colored or light-absorbing solution. The ion or element to be determined is incorporated into a stable, colored and soluble compound, or it triggers a color reaction. With a photometer the absorption of monochromatic radiation through the solution is measured. Quantitative analysis of anions and cations in a sufficient accuracy is possible.

Introduction

The basic principle is to create a colored or light-absorbing solution. The required substance or element is mounted or transferred into a light-fast, colored and soluble assembly or it causes/ actuates a color reaction. Photometry is based on measuring the absorption of monochromatic radiation through the above solution. Monochromatic radiation is obtained with the help of filters or monochromators (gratings or prisms).

Principle: If monochromatic radiation is sent through a cuvette with an absorbing solution, the luminous flux decreases depending on the depth of penetration and the concentration of the absorbing medium (i.e. the deeper it penetrates the absorbent solution and the greater the concentration of the absorbing medium). This means proportionally, the relative decrease of the luminous flux is the number of absorbing particles in the beam path. As the monochromatic radiation is sent through the cuvette plus the absorbing solution, the reflection losses at the phase boundaries and light attenuation, induced through the absorption of the cuvette walls, should be neglected.

Advantage: With the photometer quantitative analysis can be carried out at low cost.


Disadvantage: Only ions that are known and being looked for can be detected.