1. What is a spectrophotometer?
- A spectrophotometer is an instrument which measures the transmitted or reflected
energy as a function of wavelength or frequency.A typical spectrophotometer consists of
- A monochromater or spectrometer which is
used to produce a narrow band radiation source
for the measurement,
- A photometer which is used for the
energy/intensity measurement of the beam.
- A monochromater is an instrument which separates a wide band radiation. Optical
prism or the combination of two prisms, are normally used for this purpose. The
normally focused first, then goes through a slit, a collimating optical system, and
illuminates the grating. The reflected or transmitted beam is separated by wavelength
spatially, which enables wavelength selection through another narrow slit. The grating,
collimation systems have different configurations, which ensure path of the output beam
be relatively stable.
- The collimated narrow band beam from the monochromater is then used for the
The importance of a plane wave is to simplify the light path length in the media. The
passes through the sample under interest. The transmitted intensity is then collected by
detector. Between two measurements, a relative ratio can be acquired. The relative ratio
converted into the absorptance, if the other measurement is well controlled.
- Baseline is widely used in the spectrophotometry. Baseline is introduced because the
spectral distribution of the radiation source might fluctuate from time to time,
the spectral distribution is unlikely to be uniform (flat).
- A spectrophotometer belongs to one of the two main classes: a single beam or a double
spectrophotometer. This classification depends on whether the beam is split. A double
spectrophotometer is more complex, however, it is more likely to be immunized to the
temporal fluctuation of radiation source.
2. What is a spectrophotometer used for?
- A spectrophotometer is an instrument to carry spectrophotometric analysis or
spectrophotometry. The analysis itself is normally a pure physical process; however, it
more likely to be seen in a chemical, biological, environmental, quality control and
researches or even food industries.
- The instrument is also used to study solutions and liquids. a container called the
which is used, which is manufactured of high performance optical glasses. Normally a few
covettes are provided with the purchase of the instrument. The absorptive property of
covettes can be accounted into the baseline by inserting the covette with the solvent
the path in a single beam spectrophotometer.In a double beam spectrophotometer, the
absorptive property of the covettes can be accounted into the baseline in the reference
3. General specifications and tips to select a proper product for your research.
- A typical spectrophotometer includes following specifications that you might pay
to when you choose a product:
- spectral range, wavelength range or wavenumber range:
- Shows the spectrum that the monochromater/spectrometer can provide and the detector is
capable to detect. The unit for the wavelength or spectral range should be in nm or μm,
while the unit for wave number (denoted by k and k=2×p/l) range should be inverse of the
length unit. Check if it satisfies your requirement.
- spectral bandwidth:
- Explains how well the output beam from the monochromater/spectrometer tends to be
monochromatic. Normally, narrower spectral bandwidth is better.
- wavelength accuracy:
- Indicates how close the wavelength of the beam from the monochromater/spectrometer is
the value it claims to be.
- wavelength reproducibility or wavelength repeatability:
- Indicates how well the instrument can reproduce a narrow band beam for measurement.
- optical system:
- This is normally used to specify what kind of optical system is in the monochromater;
configuration, grating, etc.
- Photometric Range:
- Shows photometric measurement range, normally in Abs. For absorption in transmitted
measurement mode, T = Itransmitted/I0/I×100; and Abs = - log10(T/100) = log10(I0/I)
- Photometric Accuracy:
- How accurate the measurement will be, in Abs or Transmittance percentage
- Photometric Reproducibility or photometric repeatability:
- Shows how well the measurement value can be reproduced, normally shown in Abs.
- Size, weight, power supply requirement, etc