Spectrophotometers are scientific equipment that quantifies the concentration of a molecule in the sample of interest based on its color, translucency, and transparency.
In spectrophotometry, various spectra of light are passed through a sample whose molecules absorb light of certain wavelengths. The light that is not absorbed passes through a photodetector where the light intensity at a pre-defined wavelength is measured.
The light intensity or absorbance (A) can be used to calculate and determine the concentration of the molecules in the sample of interest.
If you’re interested in knowing more about spectrophotometers, read our comprehensive article on spectrophotometers.
Benchtop spectrophotometers are typically stationary equipment with a built-in light source. The built-in light source generates light of a specific wavelength range, allowing users to adjust and choose the desired wavelength within the detection range.
Benchtop spectrophotometers are categorized based on the range of light they detect. For example:
1. Ultraviolet and Visible (UV-VIS) spectrophotometers
Ultraviolet and Visible (UV-VIS) spectrophotometers use polychromatic light sources such as mercury line sources, deuterium lamps, and tungsten-halogen lamps to create UV and visible light. The wavelength of UV light is between 100 to 400 nanometers, while that of visible light falls within 400 to 700 nanometers.
Earlier specs used filter-photometers to remove non-targeted wavelengths and measure non-absorbed light. However, current ones use a monochromator to narrow the wavelength for the measurement of non-absorbed light. At the photodetector, the light can be measured sequentially by comparing the sample of interest to the reference sample, or a blank.
In single-beam UV-VIS spectrophotometers, emitted light travels in a single path to the samples before it is read one at a time. In double-beam UV-VIS spectrophotometers, the emitted light travels along one path to the reference and another to the sample, allowing users to read the measurement of both reference and sample simultaneously.
Alternatively, some UV-VIS spectrophotometers are equipped with linear photodiode arrays or charge-coupled devices (CCDs) so that samples are exposed to white light instead of monochromatic light. That way, samples can be measured at all wavelengths in the detection range, allowing users to gain several values from one reading.
UV-VIS spectrophotometers are useful for quantification based on the difference in color development, transparency, and translucency of the samples. They typically accommodate milli- to micro-scale samples.
2. Fluorescence spectrophotometers
Fluorescence spectrophotometers use light to excite electrons of the sample molecules. As a result, fluorescence is emitted, allowing the electrons to return to their ground states.
The light source in fluorescence spectrophotometers can be lasers, light-emitting diode (LED) lights, and mercury lamps. Typically, these light sources can create UV to infrared (IR) lights, ranging from 200 to 1000 nanometers.
Benefits of Benchtop Specs
- Their light source can provide various light wavelengths, allowing measurements of different sample types and applications.
- They are versatile and can often supply users with more than one measurement parameter.
- Some can simultaneously measure a number of samples.
- Benchtop spectrophotometers are considered “life-long” because the components of the machine can be repaired and replaced as long as they are being manufactured.
- They can be linked with an external computer or thermal printer, enabling users to export data for their records.
Limitations of Benchtop Specs
- They typically cost more than portable specs.
- Technical background and familiarity with spectrophotometry are essential to operate and obtain measurements from benchtop spectrophotometers.
- Benchtop spectrophotometers must be set up and used in laboratories.
Portable or handheld spectrophotometers are non-stationary specs, which are typically created for testing outside the laboratories. They are designed to accommodate a specific sample type or application.[1,2]
These spectrophotometers are the miniaturized benchtop spectrophotometers of similar technologies. This is achieved by tweaking the technology and modifying materials for some of the components in the machine that would reduce the size of these components.
Examples of modifications of these components are:
- Light Sources can be lasers or semi-conductors so that the space occupied by several light bulbs in benchtop spectrophotometers is considerably reduced. Semi-conductors have low-heat dissipation, which can decrease or eliminate the need for a fan in the machine that stabilizes its temperature during the operation.
- Detector Technology, including material and type, can affect the power consumption of portable spectrophotometers, contributing to the miniaturization of the machine.
Benefits of Portable Specs
- They are mobile and can be used at the sample collection site.
- Portable specs are easy-to-use, so non-technicians or persons with appropriate training can use the machine and still obtain reliable results.
- Some can be connected to external computers or printers to deposit or store measurement results.
Limitations of Portable Specs
- The range or number of wavelengths is limited in portable spectrophotometers, restricting the type of samples and tests that can be performed by the machine.
- Portable spectrophotometers are compact and often sealed. Therefore, it is generally more difficult to fix or replace the malfunctioning components inside the device.
Portable vs. Benchtop Spectrophotometers
The most obvious difference between benchtop and portable spectrophotometers is the size. Benchtop spectrophotometers are typically larger and stationary, while portable ones are smaller and mobile.
With their smaller size, portable specs are more limited in terms of their practicality and versatility. They are generally applied to a specific sample type, meaning that they can measure samples only at a specific wavelength.
However, benchtop specs require a substantial effort to set up. Benchtop devices can accommodate a wider range of samples and applications provided that the target wavelength falls within the machine’s detection range.
Here are factors that you should consider when deciding between a benchtop or portable spectrophotometer:
1. Types of Samples, Works, and Applications
In essence, benchtop spectrophotometers contain a light source that produces various light wavelengths. In other words, the detection range in benchtop spectrophotometers is much wider than in portable ones.
Thus, benchtop spectrophotometers will serve well in a laboratory setting where different types of samples, works, and applications are available and being run in parallel.
On the contrary, if your intended applications fall into point-of-use testing where only a few wavelengths are available, portable spectrophotometers are more suitable. Several portable spectrophotometers have been developed to screen for illegal substances and chemical hazards at testing sites.
For example, our portable water analyzer produces four wavelengths, which are specific for the measurement of nitrogen, ammonia nitrogen, and phosphorus content in water samples.
2. Number of Samples
Benchtop spectrophotometers typically have a larger capacity than portable ones. This means that most of them can process more samples at a single instance than portable ones.
3. User Expertise
Most commercially available spectrophotometers are user-friendly. Nonetheless, benchtop spectrophotometers are designed for users with certain technical backgrounds in mind. Conversely, portable specs are made for non-technical users or experts with minimum knowledge of analytical methods.
Benchtop and portable spectrophotometers measure the concentration of molecules based on the light intensity and absorbance at a specific wavelength.
Benchtop devices are generally designed to use in a laboratory setting, where there are a variety of samples, works, and applications. Portable spectrophotometers are more appropriate for non-experts to conduct one specific type of measurement in the field.
If you need an all-around benchtop spectrophotometer for your laboratory, check out our benchtop spectrophotometer with a LED light source.
- Gauglitz, G. “Ultraviolet and Visible Spectroscopy” Handbook of Analytical Techniques, 2nd edition, edited by Helmut Günzler and Axel Williams, Wiley-VCH, 2002, 419-452.
- Crocombe, R. A. “Portable Spectroscopy” Applied Spectroscopy, 72(12), 2018, pp. 1701–1751, https://doi.org/10.1177/0003702818809719