In microbiology, a cuvette is a device used to hold a fixed volume of solution or sample. These cuvettes are typically rimless glass tubes that can hold a fixed volume of liquid.
One type of cuvette is the membrane filter cuvette. These contain a filter that allows liquid to pass through it, usually in an upward direction. They are typically used in water testing laboratories to test the amount of bacteria in water.
When using membrane filter cuvettes, it is important to align the cuvette in the sample holder the same way each time. If you do not, then your results may be incorrect due to an incorrect comparison between samples.
This article will explain why this is important and how to correctly align your sample holder with your cuvette.
Consistency in sample collection is important for comparing results. For example, if a researcher was studying polluted water and warned people to avoid it, but claimed that most of the water was safe to swim in due to their testing method, there would be concern about the accuracy of their findings.
If the researcher rotated the cuvette each time they collected a sample, they could not guarantee that half of the volume of water in the cuvette would be toward the top each time. This could lead to an inaccurate assessment of the pollution level in the water.
Similarly, if the researcher rotated the cuvette each time they collected a sample, they could not guarantee that all of the samples would contain equal amounts of material. This could also lead to misleading results.
During sample collection, it is important to ensure the cuvette in the sample holder is aligned the same way each time.
The cuvette, which holds the liquid sample, can be rotated clockwise or counterclockwise.
The dial on the droplet controller can be set to 1 drop or 2 drops per second.
If these settings do not match the setting for 1 drop per second on the droplet controller during calibration, then the number of drops collected will change. This can lead to an error in the amount of sample collected.
By ensuring that these settings do not change between samples, more accurate results will be obtained. The same goes for ensuring that the setting for the number of drops per second does not change.
Create a standard process
When performing a sample analysis, it is important to perform each step the same way each time.
To reduce the chance of error, it is suggested to create a standard process for analyzing samples. A standard sample analysis process can include instructions such as how to prepare the reagents, how to position the cuvette in the sample holder, and how to analyze the data.
The reagents can be prepared according to manufacturer specifications, and how to check and/or change them can be part of the standard process. How to position the cuvette in the sample holder and how to analyze the data can be set parameters within the instrumentation.
Having clear guidelines for preparation, positioning, and analyzing results will help prevent error when performing an analysis.
Avoid bad habits
A bad lab habit can cost you time and money, not to mention damage to your samples or even your health.
Work in a group setting with other people? Make sure you check their work, especially when they are unfamiliar.
It’s easy to forget to do this, but it only takes one mistake to ruin everything and cost someone time and money.
Make sure everyone is aware of this so that no one else makes the same mistake.It is also important to remind people of this so that they don’t become complacent or forget.
What is the cuvette?
Inside the sample holder is a small tube called the cuvette. This holds your sample and is where the test takes place. The cuvette can be made of plastic or glass, depending on the type of test you are doing.
For some tests, it is recommended to always place the cuvette in the sample holder with the same end facing down. For example, if you are doing a glucose test, it is advised to always place the empty cuvette bottom down in the sample holder.
This tip is important because when you add the sample to the cuvette, it needs to flow down smoothly. If you placed the cuvette upside down, there would be no way for the sample to flow down!
There are some tests that require both ends of the cuvette to be filled with solution. In this case, it is recommended to place the empty cuvette bottom down in the sample holder.
Why do we care about the orientation?
It is very important to keep the cuvette in the sample holder in the same orientation each time. The reason for this is because you want to measure the same volume of water each time.
If you did not pay attention to which side of the cuvette was up and you turned it around, then you would be measuring a different volume of water. This is because you would be adding more water to the sample tube each time, which would make the reading higher.
Keeping it in the same position also helps with consistency. If you always turn it one way, then you will always have the same volume of water in the sample tube.
Can I change the orientation randomly?
No, you should always ensure the cuvette (the tube where the sample is placed) in the sample holder is placed in the same orientation each time.
The reason for this is because the sensor on your glucose monitor checks the amount of glucose in your blood by passing a limited amount of water through the device.
If the cuvette was flipped, then more water would pass through the sensor, registering a lower blood glucose level. This would give you a false reading and possibly worry you that things are okay when they are not.
What happens if I change the orientation randomly?
If you do not keep the cuvette in the same orientation, then the sample holder will pick up a different amount of fluid. This can lead to discrepancies in your results!
For example, if you had a liquid that was one inch high and you turned the sample holder upside down, it would not pick up any liquid. The more times you flip the sample holder, the less liquid it will pick up.
If you are using a manual pipette to remove the liquid, then you must keep track of how much you pull out each time. If you do not, then your results will be off.
Both of these problems can be solved by keeping the cuvette in the same orientation each time so that the holes in the cuvette line up with the sample holder.