In this guide, we will explore what a cuvette is and various aspects to consider when choosing the right type of instrument for your spectroscopy applications.
What Is a Cuvette?
Cuvettes are a type of vessel necessary for the precise spectral analysis of liquid samples. Generally used in spectroscopy, cuvettes are designed to hold liquid substances during chemical analysis. These instruments have two or four optical clear windows to ensure you can use light waves to measure the substance of interest without interference from the cuvette itself. They are often used with spectrometers, which measure how much a liquid sample absorbs or transmits a specific wavelength of light.
When you purchase cuvettes for spectroscopy, you will find a diverse selection of premium-quality options. Consider how different sizes and optical materials will influence your processes and choose the appropriate type to get precise results. The cuvette must match your application to yield accurate information on concentration and purity.
Types of Cuvettes: Why Material Matters
The cuvette you select for a sample must be transparent to the wavelengths used during the chemical analysis. The two most common cuvette materials are glass and quartz. Both options offer distinct advantages. However, factors like transmission range, cost and work environment will influence which material best suits your unique application.
- Optical glass: Glass cuvettes have a decent transmission range from 340 to 2,500 nanometers (nm). The glass performs well in spectrometers using VIS (visible) and NIR (near-infrared) light sources but will absorb light in the UV (ultraviolet) spectrum.
- UV quartz: Quartz cuvettes have an extended transmission range from 190 to 2,500 nm, making them an appropriate choice for experiments in the UV, VIS and NIR spectrums. Quartz and other UV-compatible plastics generally feature better absorption across a broader wavelength range — a requirement for measuring samples in spectrometers with UV-VIS light sources.
- IR quartz: The transmission range for IR quartz cuvettes is 230 to 3,500 nm, allowing for some of the UV spectrum and an extended range in the infrared (IR) as well. An IR quartz cuvette may be required to offer greater advantages in IR applications where you need the highest sample purity.
How to Determine Cuvette Volume
The volume of a cuvette is the maximum amount of liquid sample that it can safely hold. To calculate the volume of cuvettes, use the formula:
Inner Length x Inner Width x Inner Height x 80% = Cuvette Volume
A cuvette will accommodate 1 milliliter (mL) of sample per every 10 millimeters (mm). When running this calculation, remember to convert the cuvette’s length, width and height from mm to mL. For example, the most widely used cuvette is a square type with an internal size of 10 x 10 mm and a 43.75 mm internal height. The calculation for a 10 mm square cuvette would be:
1 mL x 1 mL x 4.375 mL x 80% = 3.5 mL
These cuvettes may hold up to 4.375 mL when filled to the edge, but the cuvette volume is determined at 80% capacity. The reasoning is that you should only fill a cuvette 80%. When liquids are too close to the top, the sample is more likely to spill onto your lab station, spectrometer or gloved hands. This event can pose a danger and may cause problems during your measurements. The cuvette volume of a 10 mm square cuvette is therefore 3.5 mL, the amount it can safely hold.
Cuvette Volume Options
There are four types of cuvette volume options available:
- Macro cuvettes hold a measuring volume greater than 3.5 mL. Among these types are common cuvettes ranging from 7 to 35 mL.
- Standard cuvettes hold a measuring volume of 3.5 mL. A standard cuvette will fit in most spectrometers.
- Semi-micro cuvettes hold a measuring volume of 0.35 to 3.5 mL. To hold the smaller sample, these cuvettes must use a spacer, mount or standard cuvette exterior with a tapered interior.
- Sub-micro cuvettes hold a measuring volume of 20 microliters (µl) to 350 µl. This cuvette is designed to measure through a specific z dimension, so it must match the beam’s height.
How to Determine Cuvette Path Length
The cuvette path length is the interior distance between a cuvette’s parallel optical windows that a particular wavelength of light must traverse through. Spectrometers have a standard chamber size in which the cuvette is placed during chemical analysis. That’s why it is essential to select a cuvette that will accommodate your spectrometer’s chamber size.
To determine the path length, you need the cuvette’s outer dimensions and the wall thickness. Because light will pass through both the front and back windows, remember to double the wall thickness when following this formula:
Outer Dimension – (Wall Thickness x 2) = Path Length
A standard 10 mm square cuvette is actually 12.5 mm measured from the outside. Its wall thickness of 1.25 mm brings the measuring space to 10 mm, the same dimension used for most spectrometer chambers.
Shorter and longer path length options are also available. A cuvette spacer or mount can help accommodate shorter path length cuvettes in standard spectrometers. While 10 mm path lengths are the most widely used, absorption cuvettes come in path lengths ranging from 1 mm to 100 mm, as well.
Importance of Selecting the Right Cuvette by Application
The sample type and the processes you intend to complete can influence your cuvette selection.
The primary factors to consider when selecting the right cuvette are:
- Material: The cuvette material’s transparency will highly depend on the wavelength of light used in the spectrometer. Different materials offer unique light-passing properties, meaning particular materials are necessary for specific applications.
- Volume: Consider the volume requirements of your experiment as well as the z dimension of the spectrometer. Depending on where the light exits the machine, the cuvette window will require a particular height that the sample volume needs to meet.
- Size: The spectrometer will also dictate the maximum cuvette path length you can use. Other factors that could influence the cuvette’s size include the sample type, volume requirements, concentration levels and measurements you need to make.
Cuvettes come with two or four polished sides. Most absorption cuvettes have two clear windows to allow maximum light transmittance through the sample linearly. Contrarily, scattering and fluorescence applications require the signal to be measured at 90 degrees to the light beam. For example, fluorescence cuvettes have all four sides polished to help with successful fluorescence experiments.
Choosing the Right Type of Cuvette From Spectrecology
The experts at Spectrecology are here to help you select the correct cuvettes for your needs. Contact us online or shop online to explore the performance capabilities of our products today. We can provide guidance based on your specific needs and help you select an appropriate cuvette for your sample type, application, budget and more!