How to select the right cuvette material for UV- VIS absorbance studies?

How to select the right cuvette material for UV- VIS absorbance studies?
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Spectrophotometer Cuvettes (Image Courtesy : http://www.sciencebuddies.org/)

Absorbance studies have become a base for examining various solutions and particles. Under these, the light gets passed through the solutions in a defined format.

However, Common laboratory absorption studies involve liquids – either as pure solvents or solutions of light absorbing compounds in transparent solvents. This brings in the need for a container that could hold these liquid substances.

Usually, a container of precise dimensions, i.e., 10mm path length, gets used here. These are called cuvette spectrophotometers, and they are transparent to the wavelength of light required for the purpose. Therefore, it doesn’t cause any problems during the study. 

The only issue here is that we can’t define the cuvette this simply because of the available diversity of materials with which they are made. So one may easily get confused about which alternative to use. Let’s first understand their basic material requirements, and then we will draw a contrast between different types of cuvettes.

What Are Cuvette Spectrophotometers Made of?

Cuvettes are commonly made from different transparent materials such as optical glass, quartz or transparent plastic. At first sight all such materials appear to be perfectly transparent and fit for all types of absorbance studies.However, each material has unique light absorbing properties and it is important to know about such optical characteristic properties before making your selection of the cuvette material.

In case you don’t give importance to these factors about cuvette used in UV spectroscopy, you will end up creating trouble in the absorbance studies, and the obtained results won’t be accurate.

The article examines the optical characteristics of such materials that will help you make the right choice before proceeding with absorbance measurements.

Irrespective of the material selected it must be borne in mind that cuvettes, except for transparent plastic cuvettes, are fragile and require careful handling. The earlier article titled Proper care and handling of UV – Vis absorption measurement cells highlights the precautions required in careful handling of cells and on ensuring a high degree of accuracy of your measurements.

So let’s move on to the available types of cuvettes.  

Various Materials Used in the Making of Cuvette for Spectrophotometry

Some of the common materials you can find cuvette in are:

Optical Glass Cuvette:

Glass cells are most common in school and college undergraduate laboratories because of their lower cost. Optical glass shows absorbance throughout the visible and IR regions extending from nearly 340 nm to 2500nm covering majority of organic and in inorganic species. However, glass absorbs strongly in UV region and its application is not recommended for wavelengths below 340 nm.

Plastic Cuvette:

Like glass transparent plastic cuvettes find application in absorbance measurements in visible region. The additional benefit is that such cuvettes are unbreakable but on the other hand they cannot be used in UV absorbance studies as well as with certain organic solvent compounds

Quartz Cuvette:

Quartz is expensive in comparison with glass and transparent plastics but has the additional benefit of covering both UV and visible regions right from 190 nm. However, it is even more fragile than glass and the cuvettes need to be handled with greater care.

Now that you have seen the individual properties of these materials, let’ move on to their comparison and examine which one will fit best. 

Comparing Cuvette Spectrophotometer

Here are some of the factors based on which you can understand the difference between plastic cuvette vs. glass cuvette vs. quartz cuvette.

  • Cost: Cost is a crucial aspect in determining any laboratory equipment or solutions. The most cost-efficient cuvette in the provided options is plastic. Then comes the optical glass cuvette, and finally, the quartz cuvette. So when you are tight on budget, plastic will be a great alternative to go with. 
  • Reusability: Plastics are usually disposable. You can use them once or a few times, as directed by the manufacturer. Then you will have to change them. On the flip side, both glass and quartz are reusable materials. If you maintain them properly, they will remain in good shape for a long time. 
  • Transparency: The simple rule for this factor is to check which material has the most ‘light transmission,’ therefore, remaining transparent during the study. Quartz stands out in this aspect. The material remains transparent in both visible light and UV ranges. That is why it can be easily used for UV-light spectrum sample measurements. Contrastingly, glass and plastic materials are generally ideal for visible light studies and can’t be used for purity and concentration measurements. 

Apart from these characteristics, there is another benefit of quartz, i.e., the highest temperature resistance. It has to be kept in mind as well while picking up a suitable cuvette. 

By now, it must be clear to you that all of the available types of cuvettes are great in some aspects. In order to choose one, the specific use and equipment have to be defined. For example, plastic may not be efficient for UV-range experiments, but it is a cost-effective alternative for all the visible light studies. 

It is important to bear in mind that oxygen present in the atmosphere absorbs significantly below 200 nm and nitrogen absorbance assumes significance below 190 nm. Absorbance measurements made below 200 nm should be conducted with oxygen free nitrogen purging of sample compartment. However, for measurements below 185 nm it is best to maintain vacuum in the sample chamber.

A blank reference measurement provides highly reliable results but for the purpose cell pair with optically matched windows should be used to prevent any absorbance mismatches.

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