The basics of spectrophotometry

Colour is everywhere in our daily lives. Did you know you can measure colour? The spectrophotometer is an essential tool for biologists and technicians when analysing chemical and biological samples.

Measuring colour

In simple terms, colours are dependent on light. We do not actually see colours, rather what we see as colour is the effect of light shining on an object. When white light shines on an object, it may be reflected, absorbed, or transmitted. Glass transmits most of the light that comes into contact with it, thus it appears colourless. Snow reflects all of the light and appears white. A black cloth absorbs all light and so appears black. A red piece of paper reflects red light better than it reflects other colours. Most objects appear coloured because their chemical structure absorbs certain wavelengths of light and reflects others.

The colour variation of a system that undergoes a change in concentration of some component is the basis of colorimetric analysis.

What is Colourimetry?

Colourimetry is simply the measurement of colour. Colourimetry is the determination of the concentration of a substance by measurement of the relative absorption of light with respect to a known concentration of the substance. In visual colourimetry, natural or artificial white light is generally used as a light source and determinations are usually made with a simple instrument termed a colourimeter or colour comparator. When the eye is replaced by a photoelectric cell, the instrument is termed a Photometer vs Spectrophotometer.

Photometer

HI83399 Benchtop Photometer

A photometer isolates a specific wavelength of light by using filters. A colourimeter uses edge band filters, or some similar system, to separate light out into colour components, and then fits those to matching curves based on the human eye, to produce colour values based on what the human eye would see. This is ideal for matching the human visual response but tells you nothing about data invisible to the human eye, such as emissive spikes at narrow points in the spectrum; that’s spectral data and requires a spectrophotometer.

Spectrophotometer

HI801 IRIS Spectrophotometer

Spectrophotometers are different from photometers as they allow for measurement in the spectrum of all wavelengths of visible light and not just pre-specified wavelengths. Spectrophotometers work by isolating light at specific wavelengths from white light. A spectrophotometer breaks light up into a spectrum, using a colour grating or similar system. Then an array of sensors reads each section of the spectrum, producing spectral data. This is ideal if you are analysing the spectral emissions of a lightbulb, a star, or some other light source, which is why spectrophotometers are often used as scientific devices.

Best uses for a spectrophotometer 

Split beam optical system, customisable methods and rechargeable battery. The iris portable spectrophotometer is unlike any of the products Hanna Instruments has created in the past. It is different from the company’s photometers as it allows for measurement in the spectrum of all wavelengths of visible light and not just pre-specified wavelengths. Spectrophotometers work by isolating light at specific wavelengths from white light. This compact meter incorporates several features that facilitate both fantastic performance and exceptional usability.

  • Advanced split beam optical system
  • Rechargeable li-ion battery
  • User customisable methods

Today’s spectrophotometers are designed to be both durable and portable, offering flexibility in use. While the applications are nearly endless, some of the best uses include:

  • Elemental determination for water quality
  • Enzymatic analysis in wine
  • Analysis of fertiliser properties for agriculture.

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