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Introduction
Any material that is transparent to the required wavelengths can be used to make a cuvette. And a wide selection of cuvette volume is available. The sub-micro cuvettes can be as small as 10 microliters (or less), while the macro types can hold up to 35 milliliters (or more).
Any material that is transparent to the required wavelengths can be used to make a cuvette. And a wide selection of cuvette volume is available. The sub-micro cuvettes can be as small as 10 microliters (or less), while the macro types can hold up to 35 milliliters (or more).
The length of light passing through the cuvettes containing sample solutions is called path length, which has an effect on the absorbance value calculation. Many cuvettes have a standard light path of 10 mm (0.39 in), which makes the calculation of the absorption coefficient easier.
10mm Path Length Cuvettes
Most cuvettes for absorption measurements have two parallel transparent sides so the spectrophotometer light is able to pass through, though some special tests require only one single clear side. For fluorescence sample measurements, two parallel clear sides and additional right angles sidewalls clear are also necessary for the excitation light. PTFE caps, stoppers, or screw caps are used with hazardous or evaporative solutions to protect samples from the air.
It can be complicated and confusing if you are new to the field of selecting cuvettes for UV-vis spectroscopy. Not all cuvettes work for every application, and some basic knowledge is useful to make the decision. The article will help you walk through the most important factors to consider when making a final decision.
How do you define a cuvette?
A cuvette (French: cuvette = “little vessel”) is a small tube-like container with straight sides and a circular or square cross-section. They’re normally sealed on one end and have a cap to seal the other.
To prevent refraction artifacts, regular types of cuvettes have a square or rectangular cross-section. The majority of the cuvettes are used in spectrophotometers, colorimeters, and fluorometers.
A cuvettes is a small glass/quartz/plastic lab vial which is used to hold solutions (or powder in some circumstances) for spectroscopic experiments. When a light beam passes through the sample within the cuvette, the absorbance, fluorescence intensity, transmittance, fluorescence polarization, or sample fluorescence lifetime are measured. The testing of measurement is performed with a spectrophotometer.
Simple Spectrophotometer Design
The materials available for cuvettes are optical glass, plastic (PMMA or PS), UV quartz and IR quartz. The plastic cuvettes are much less expensive than quartz materials thus they can be used as disposable to avoid cross contamination in fast spectroscopic assays. Quartz or glass cuvettes are necessary for organic and corrosive sample solutions. Generally speaking, glass or quartz cuvettes have a higher transmission rate and accuracy of data compared with plastic materials, and these materials of cuvettes can be reused many times if properly used.
Quartz with Q, Glass with G, and Plastic cuvettes
Understanding Cuvette Path Length
The cuvette path length is the distance at which light travels through the inside walls of a rectangular cuvette. A typical spectrophotometer cuvette path length is the inner length between two clear parallel walls. The standard and most used path length is 10mm. And the cuvette’s most common exterior dimension is 12.5 x 12.5mm, with a height of 45mm, which makes the wall thickness of 1.25mm.
12.5×12.5 mm External Cuvettes
Besides 10mm standard cuvette path length, shorter path lengths (from 0.1mm) and longer types (up to 100mm or longer) are also available for different volume sizes. We’ll discuss in more detail below.
Optical Path Lengths Vary from 0.1 – 100mm
Tolerances for Path Length
Our cuvettes are manufactured with a path length tolerance of ±0.05mm. In other words, the 10mm standard cuvette can vary in path lengths between 9.95 – 10.05 mm. Or for 20mm cuvettes, the path length could be from 19.9mm to 20.1mm.
Dual Optical Path Length Cuvettes
With a dual path length cuvette, it’s possible to have both short and long path lengths in the same cuvette cell at the same time. For example, a 1mL size 4 clear walls cuvette can have dual path lengths of 3mm and 10mm in the same cell.
You can decide which path length to be used for a dual path cuvette by placing different sides in the spectrophotometer / fluorometer. For instance, a 10 x 3 mm dual path cuvette, if the light source passes through the small window, the path length is 10 mm and if light passes the bigger window (rotate 90 degrees), the path lengths will be 3 mm.
Different commonly used dual-path lengths cuvette available such as:
A variety of commonly used dual-path cuvette are available with us:
- 2 x 10 mm
- 5 x 10 mm
- 10 x 20 mm
- 10 x 50 mm
Dual-Path Lengths Cuvettes
Types of Cuvette Materials
Previously, reusable quartz cuvettes were necessary for measurements in the ultraviolete (UV) range, because most plastics and optical glass materials absorb the ultraviolet light, resulting in interference. Now a few types of specialized plastic cuvettes are also transparent to UV light ranges. Optical Glass, plastic and all quartz material cuvettes are transparent to visible light ranges.
Quartz Material is Transparent to UV but Glass is not
As the most prominent factor to consider when choosing a suitable cuvette is the material, we are going to compare these materials in more detail below:
- Optical Glass
- UV Quartz
- IR Quartz
- Plastic
While each of these materials has some advantages, it also has some disadvantages. Again counting on your experiment requirements, you should decide which of the materials are the best. Let’s start with optical glass material.
Optical Glass
Optical glass material cuvettes are a good choice if you have a tight budget and the desired wavelength range is visible spectral (340 – 2500 nm). The material also has a decent transmission rate of >80% at 350nm. Most measurements will fall into this area and it’s not necessarily required to have the extra UV quartz material range (190 – 340 nm) for lots of applications.
Types of Glass Cuvettes
UV/ES Quartz
Another option is UV quartz, which is a step above glass material. If you got some extra budget, UV quartz material would be a nice choice that you can get a measurement transmission range of 190 – 2500 nm. If you are performing UV experiments, a UV quartz cuvettes would be an absolute need and it’s important not to cut cost to this range as the data will most likely not be up to par if the choice is a low cost, low quality UV cuvette cell. ES quartz glass material has a higher transmission rate than UV quartz material, which is used on our All Fused or High Transmission types of cuvettes and cells.
Types of Quartz Cuvettes and Cells
IR Quartz
For UV visible IR measurements, IR quartz material cuvettes will be an outstanding choice. The range of transparency is 220 – 3500 nm so part of UV, all range visible, and extended range in the IR are all covered at the same time.
IR Quartz Cuvettes
Plastic
When high speed is more critical than high accuracy of measurement, plastic cuvettes are a nice choice to be used in fast spectroscopic samples. Available usable range of 380 – 780 nm (the visible spectrum range) , plastic cuvettes are disposable after use, which benefit of no cross-contamination. Being cheap to manufacture and purchase, disposable plastic cuvettes have been widely used in some research labs where the beam light is not high enough to have an effect on the absorption consistency and tolerance value.
Material Transmission
Different Material Transmission Range and Suitable Applications
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| Material | Wavelength | Transmission Rate | Usage | Application |
| Optical Glass | 340-2,500nm | 80% at 350nm | Reusable | Visible |
| ES Quartz Glass | 190-2,500nm | 83% at 220nm | Reusable | UV-visible |
| UV Quartz Glass | 190-2,500nm | 80% at 220nm | Reusable | UV-visible |
| IR Quartz Glass | 220-3,500nm | 83% at 2730nm | Reusable | UV-visible-IR |
| PS or PMMA | 380-780nm | 80% at 400nm | Disposable | Visible (Optional UV) |
Transmission of Empty Cuvettes Made of Different Materials
Cuvette Chemical Resistance
Above cuvette materials, quartz or glass cuvettes have different fabrication types which can significantly affect the cuvette prices with the same design and materials. There are four types of cuvettes available with us (price from low to high): GLUED, POWDER FUSED, HIGH TRANSMISSION, and ALL FUSED.
Image: outlook comparison of different cuvette fabrication types
Aqueous sample solutions have the least requirements in terms of material and fabrication types. All plastic or glass or quartz cuvettes will work and glued cuvette is often a great choice with cheap prices. Especially when you need to customize some cuvettes, glued cuvettes can save a lot in budget and much shorter lead time compared with the Powder Fused or All Fused types.
When performing experiments of organic or corrosive solvents involved, instead of glued or plastic material, optical glass and quartz material will be the preferred choice as these two materials are much more robust. The glued cuvette bonds will be dissolved by organic solvents, instead, Powder Fused and All Fused cuvettes will work for most of these situations.
*ALL FUSED:
These cuvettes are molded and fabricated as one piece and made of ES quartz material.
Features:
- Resistant to high temperature (<1200℃)
- Resistant organic and corrosive chemicals
- Highest Transmission compared to other materials
- Zero data reading variation is available on request (default <0.3%)
Note: These ALL FUSED cuvettes can be used with most popular organic solvents, as well as acids and bases. They are compatible with chemicals such as acetone, butanone, DMF, and concentrated hydrochloric acid.
*Powder Fused:
These cuvettes are made of UV quartz materials and are most cost-effective. Bestsellers.
Features:
- Resistant to high temperature (<600℃)
- Resistant most organic and corrosive chemicals
- High transmission rate
This type of cuvettes is resistant to most organic solvents, acids, and bases. However, it has a chance to be stained by some chemicals to the bonding edges. It’s a much cheaper alternative to the ALL FUSED type.
*High Transmission:
High transmission cuvettes have the same features and specifications as powder fused except for a higher transmission. They are made of ES quartz glass material.
Note: please don’t use the Powder Fused or High Transmission cuvettes to store chemicals for a long time. Clean them after use.
*Glued:
These cuvettes are assembled with glue and are the simplest way of customization.
Features:
- Non-resistant to high temperature (<100℃)
- Non-resistant organic and corrosive chemicals, use with aqueous samples only
- High transmission rate
Note: Please note that these glued cuvettes should not be used with benzene, toluene, aqua regia, ethanol, corrosive solutions, or other similar substances, as they may degrade the bonds between the pieces and cause the cuvette to leak. DO NOT rinse the cuvette with ethanol or similar solutions for cleaning.
| 0 | 1 | 2 | 3 | 4 | |||
|---|---|---|---|---|---|---|---|
*ALL FUSED | *POWDER FUSED | *HIGH TRANSMISSION | *GLUED | ||||
UV vis ( 190 – 2500 nm) | ✔ | ✔ | ✔ | ✔ | |||
NIR ( 260 – 3500 nm) | ✔ | ✔ | ✔ | ✔ | |||
Glass ( 350 – 2000 nm) | ✔ | ✔ | ✔ | ✔ | |||
Matched Pair | ✔ | ✔ | ✔ | ✔ | |||
Transmission > 80% | ✔ | ✔ | ✔ | ✔ | |||
Transmission > 83% | ✔ | ✖ | ✔ | ✖ | |||
Resistant to Acids and Bases | ✔ | ✔ | ✔ | ✖ | |||
Resistant to Organic Solvents | ✔ | ✔ | ✔ | ✖ | |||
Usable upto 600°C (1112°F) | ✔ | ✔ | ✔ | ✖ | |||
Usable upto 1200°C (2192°F) | ✔ | ✖ | ✖ | ✖ | |||
0 Variations Reading | ✔ (On Request) | ✖ | ✖ | ✖ | |||
Fabrication | Molded | Assembled with Quartz Powder | Assembled with Quartz Powder | Assembled with Glue | |||
Storage | Long Term | Clean after Use | Clean after Use | Clean after Use | |||
Available Material | Quartz Material | ||||||
Understanding Cuvette Volumes
In addition to the above factors, you should choose the cuvette size to hold the samples. The cuvette volume is the maximum solution volume that a cuvette can hold safely.
The standard and most commonly used cuvette volume is 3.5mL for a 10mm x 10mm inside dimension cuvette cell. But how is this volume configured?
3.5mL is Standard Most Commonly Used Cuvette Volume
How can you figure out the volume of a cuvette?
It could be a simple math in calculating any cuvette volume. As the standard 10x10mm cuvette is 3.5mm, we can easily figure out the standard cuvette with 10mm and path lengths range from 1-100mm. See chart below:
1-100 mm Standard Cuvette Volumes
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| Path Length | Outer Dimension | Inner Length | Inner Width | Volume |
| 0.1mm | 2.6 x 12.5 x 45mm | 0.1mm | 10mm | 30uL |
| 0.2mm | 2.7 x 12.5 x 45mm | 0.2mm | 10mm | 70uL |
| 0.5mm | 3.0 x 12.5 x 45mm | 0.5mm | 10mm | 170uL |
| 1mm | 3.5 x 12.5 x 45mm | 1mm | 10mm | 0.35mL |
| 2mm | 4.5 x 12.5 x 45mm | 2mm | 10mm | 0.7mL |
| 5mm | 7.5 x 12.5 x 45mm | 5mm | 10mm | 1.7mL |
| 10mm | 12.5 x 12.5 x 45mm | 10mm | 10mm | 3.5mL |
| 20mm | 22.5 x 12.5 x 45mm | 20mm | 10mm | 7mL |
| 30mm | 32.5 x 12.5 x 45mm | 30mm | 10mm | 10.5mL |
| 40mm | 42.5 x 12.5 x 45mm | 40mm | 10mm | 14mL |
| 50mm | 52.5 x 12.5 x 45mm | 50mm | 10mm | 17.5mL |
| 100mm | 102.5 x 12.5 x 45mm | 100mm | 10mm | 35mL |
0.1 – 100 mm Standard Cuvettes
But how is the standard cuvette volume 3.5mL calculated? Here is the formula we use:
The cuvette inner dimension with a thickness of 1.25mm:
L (12.5-1.25) x W (12.5-1.25) x H (45-1.25) x 80%=3.5mL
You might wonder why is 80% of the total inner volume applied?
That’s because you are supposed to fill the cuvette only up to 80% to avoid an easy spill which causes much trouble during the testing measurements.
Should I always fill the cuvette upto 80%? What’s the minimum quantity to use?
It depends on the Z dimension of your instrument. The Z dimension is the laser height, which means how height your instrument light source is, which usually comes in 8.5, 15, or 20mm.
The sample solution should be at least as high as 12mm to cover the light source height of for example 8.5mm Z dimension. So for the 3.5mL standard cuvette, the minimum volume should be: 10.7-3.5mL:
10mm x 10mm x (12mm-1.25mm)≈10.7mL
So for Z dimension of 15mm, the usable volume is 1.8-3.5mL:
10mm x 10mm x (19mm-1.25mm)≈1.8mL
Note: 1.25mm is the cuvette bottom thickness.
Are there any exceptions? Any cuvettes to be always filled?
The answer is yes. For ultra micro-volume cuvettes or flow-through cells, when the testing solution volumes are very limited, 10 – 400uL, it is required to withhold enough samples to make sure the light source will be able to pass through the solutions.
Now you got the idea of how the cuvette volume calculated. Next, we’ll move to a new section that covers more details of the Z dimensions mentioned above, which is very important to consider when choosing ultra micro cuvettes from 10 – 350uL.
Micro Volume Cuvettes
What is the Cuvette Z dimension, Exactly?
The Z dimension is the distance from the cuvette bottom to the center of the cuvette aperture (the small window the light will pass through).
Z dimension is important to ultra micro cuvettes and flow-through cells where the measurement window is very limited.
Why is Z Dimension so important?
You will not be able to use the cuvettes with wrong Z dimensions. It’s critical to order the cuvette with the correct Z dimension when the measurement window is very small.
For example, if you order a 100uL sub-micro cuvette, with a 15mm Z dimension. The measurement window is only 5mm high and when using it to 8.5mm Z dimension spectrophotometer, the instrument light source cannot reach the bottom of the window so there will be no data reading. You should choose the correct Z dimension before you proceed to order.
Why does the Z dimension differ between instruments?
To ensure that their instrument performs optimally, each instrument manufacturer takes engineering decisions for its design and Z dimension sizes. The optical and engineering decisions are made to ensure that the instrument performs to its published requirements which determine the height, width, focus, and location of the light beam in any instrument.
How can I decide the Z dimension of my spectrophotometer?
The correct Z dimension or Z height or center beam height for an instrument should be detailed in the literature supplied by the manufacturer with the instrument.
The Z dimension or center beam height for an instrument should be defined in the literature or user manual given with the instrument by the manufacturer.
If you are not sure, please send us an email (sales@cotslab.com) to help determine the Z dimension of your instruments.
Cuvette Caps
There are a variety of caps and bottoms available, as well as different cuvettes, to fit your own experiment needs. It could be a bit complex for the purchasers when making the initial decisions.
For various budgets and sealing requirements, different cuvette caps are available.
| 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|
| Type | Material | Sealing | Injection | Price |
| PTFE Lid | PTFE | ★☆☆☆☆ | No | Low |
| Silicone Lid | Silicone | ★★★☆☆ | No | Low |
| Silicone Lid w Hole | Silicone | ★★★☆☆ | Needle Injection | Low |
| Stopper Cap | PTFE | ★★★★☆ | No | Medium |
| Screw Cap with Septa | PTFE | ★★★★★ | No | High |
| Screw Cap with Hole | PTFE | ★★★★★ | Needle Injection | High |
