How do I choose a spectrophotometer?
Spectrometers, or spectrophotometers, are analytical instruments used to identify or confirm the chemical species, chemical structure, or concentration of substances in a sample. Spectrophotometers will emit an energy source to pass through a solution and measure light intensity at different wavelengths. If the solution is high in molecular concentration, then more light will be absorbed. In most cases, a sample submitted for spectrometric analysis must be very pure to avoid poor or contaminated results. Spectrometers are generally comprised of a light or energy source (typically a lamp), a filter (or monochromator) to set desired wavelengths of which to read, a place for cuvettes or blanks, and a radiation detector (or phototube) to convert the energy received during the experiment into a measurable signal.
Important criteria to consider when selecting a proper spectrophotometer/spectrometer:
- Detection limits
- The density, shape, or size of the product you wish to measure
- Wavelength range
- Analytical working range
- Sample throughput (single sample vs. multi-sample)
- Data quality
- Cost of instrument and associated consumables
- Customizable and/or pre-configured method options
- Measurement time
- Footprint of instrument
What is the difference between single beam, double beam (dual-beam), and split beam spectrophotometers?
A single beam spectrophotometer has only one beam of light, while a double beam spectrophotometer has two beams of light, one passing through a reference solution and one passing through the sample. In single-beam instruments, because there is only one light path which passes through the sample, it therefore requires manually switching a reference cuvette with the sample cuvette for calibration. Double beam spectrophotometers operate faster and provide more reproducible results because they perform an automatic correction for the loss of light intensity as the beam passes through the sample and reference solution. Split-beam instruments are like dual-beam systems, but instead use a beam-splitter which rapidly alternates the light path between the reference and the sample while using one detector.
Guidelines for evaluating cuvettes
Windows: Cuvette windows should be uniformly clear, with no scratches, clouding, inclusions, bubbles, streaks, or “rainbowing,” as these issues will negatively affect the performance of the cuvettes. Scratches on non-optical sides are negligible.
Mold markings: Ideally, a single box of cuvettes should have identical mold markings. If they are not identical, then they may not have come from the same mold cavity and will be inherently more inconsistent in measurement.
Performance: Test your cuvette by running it several times in your spectrophotometer. It is always a good idea to rotate it 180 degrees and retest. Values should be very close. If results are inconsistent, it could be due to poor molding or a poor fit in the cuvette holder. If values differ significantly, the cuvette windows are likely inconsistent from one side to another. Window inconsistencies, thickness, and quality of resins used make a big difference at critical wavelengths during testing and use.
Shop Glass and Quartz Cuvettes to suit your analytical needs
Calibrating your instrument
To calibrate a spectrophotometer, a reference solution is used to zero out the instrument. This solution provides a base or zero reading. The device is then calibrated by placing the reference solution inside the spectrophotometer, zeroing out the settings, and running the instrument. You can then test your material with confidence that your machine is working properly.
A variety of spectrometers are available on the market. Here is what you can find on coleparmer.com.
UV/Visible Spectrophotometers: A second lamp—usually deuterium—turns a visible light spectrophotometer into a UV-visible unit that can measure from 190 nm to 1100 nm. UV-visible models are available with a variety of features including scanning function, multiple cells, integral printers, and user interfaces.
UV/Visible Spectrophotometers with CPLive connectivity: Upload results and protocols safely and securely to the cloud, share data with your colleagues, and simultaneously manage multiple devices through the CPLive app on your computer, tablet, or smartphone. All your information, from one or multiple instruments, is now stored in one secure location, so data is never lost.
Visible Light Spectrophotometers: Simple spectrophotometers use only visible light (320 to 1000 nm) produced by a tungsten lamp. Portable and benchtop models with a continuous wavelength range are most commonly used for routine laboratory work. Choose from analog and digital models that feature optional data acquisition software for your PC.
Mercury Spectrophotometer or Analyzer: An economical alternative to atomic absorption systems, the mercury analyzing spectrophotometer quickly measures trace amounts (0 to 9 µg) of mercury in potable, surface, saline, or wastewater.
Fluorometer: A fluorometer measures the fluorescence released when a sample is exposed to a single wavelength of light.
Browse all Spectrophotometers/Spectrometers available from Cole-Parmer
|Industry ||Surface ||Color meter and spectrophotometer models |
|Painted surfaces ||Flat panels || |
12-mm 45/0 cone, 12-mm hemisphere,
26-mm, 11-mm benchtop
|Curved surfaces ||3-mm, use foam baffle |
|Masonry, stucco, cement ||20-mm D with window and baffle |
|Plastics ||Flat areas ||12-mm cone |
|Small parts ||3 mm |
|Curved surfaces ||3-mm, use foam baffle |
|Wire and cable ||Small wire and fiber special, 3-mm and fixture |
|Fibers and small tubes ||Up to 5-mm D, wire and fiber special |
|Textured surfaces ||20-mm D with window, 12-mm hemisphere |
|Powders ||12-mm or 20-mm with window, |
30-mm bench top
|Transparent ||12-mm with white background |
|Foods and |
|Cheese, meats ||12-mm w/window, 20-mm D w/window |
|Powders, flour, sugar ||20-mm D w/window, 30-mm bench top |
|Fruits, outside ||12-mm cone |
|Fruits, inside and fish ||12-mm with window |
|Leaves, small areas ||3 mm |
|Soil and grass clippings ||20-mm D w/ window, 30-mm bench top |
|Coffee, grains, snack foods ||30-mm bench top |
|Opaque liquids, sauces, dips ||30-mm bench top |
|Graphic arts ||Litho printing ||3 mm |
|Other printing small ||3 mm |
|Ink proofs, larger print targets ||12-mm cone |
|Paper ||Finished paper ||12-mm, 11-mm bench top |
|Paper pulp and paper board ||20-mm D w/ window |
|Textile ||Textile printing ||3 mm |
|Hard weave ||12-mm cone |
|Solid colors soft weave ||20-mm D w/window, 30-mm bench top |
|Packages ||12-mm cone |
|Cosmetics ||Foundation drawdowns ||12-mm cone, 11-mm bench top |
|Skin, cosmetics on skin ||12-mm flat head |
|Powders and creams ||12-mm or 20-mm with window, |
30-mm bench top
|Lipstick ||12-mm with thin film press |
|Packaging ||3 mm |