Photometers are photometric measurement instruments that can be used to measure the concentration of organic and inorganic compounds in solution by determining the absorbance of
specific wavelengths of light. Integral to water quality analysis, photometers go beyond simple testers by allowing users to develop a chemical profile of the sample rather than just
simple detection of the presence of a chemical compound.
Photometers have many laboratory and practical applications. Besides being valuable for basic research in chemistry and biology laboratories, they are valuable tools for measuring water
quality by determining the concentration of a wide range of substances and contaminants such as heavy metals, radionuclides, nitrates, phosphates, fluorides, pesticides, and many others.
They can also be used to measure the concentrations of plant nutrient such as phosphorus, nitrate and ammonia in the soil.
Photometer Technology
When testing for water quality, most organic and inorganic compounds are colorless and undetectable to the human eye. Testing with a photometer introduces chemical reagents and light
providing a way to “see” these invisible compounds.
Reagents are chemicals formulated to react with specific ions causing them to change color. For the purpose of water quality analysis, test samples are put in a cuvette (sample container)
to which reagents are added. If the compound specific to the reagent is present, the reagent will turn it a color. The greater the concentration of ions, the deeper the coloration. In order
to convert this color into a numerical value, light is required.
White light consists of numerous wavelengths of light which correspond to different colors. If that light is passed through a test solution which has been colored by a reagent, one color,
or band of the wavelength of white light, is absorbed. The wavelength of light absorbed is a function of the ion present. Different chemical substances absorb different wavelengths of light
on the visible spectrum.
Photometers are designed to measure multiple ion types and are thus equipped with filters able to isolate multiple (often up to 5) wavelengths of light. Beyond the multiple wavelengths,
photometers operate much like colorimeters. In a cuvette, test samples are combined with reagents which colorize specific ions. Certain wavelengths of light are passed though the cuvette.
Some of the light is absorbed by the colorized test sample depending upon which ions are present and their concentration. Any light that passes through the solution is measured by photodiode
or photocell . According to the Beer-Lambert law, the quantity of light absorbed by a substance dissolved in solution is directly proportional to the concentration of the
substance.
Like colorimeters, photometers measure the concentration of an ion. Also like colorimeters, though transmittance (a linear scale from 0-100%) or absorbance
(a logarithmic scale from zero to infinity) are the measured values, the displayed values are usually mg/L or ppm which are calculated from measured values.
Things to Consider When Selecting a Photometer:
- What chemical ions are being tested for?
- Is a single parameter tester suitable for your needs or are multiple parameters needed?
- What consumables (reagents and cuvettes) are required?
- What level accuracy is needed?
- Are any advanced features such as data logging or communications needed?
If you have any questions regarding photometer please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.
