A volumetric flask is a piece of laboratory glassware mainly used to accurately measure specific quantities of liquids at a particular temperature. It is mostly used in chemistry. A volumetric flask is much more precise when compared with beakers or Erlenmeyer flasks. It is normally pear-shaped with a flat bottom. They are available in classes A and B where class A is recognized in being the highest in accuracy.
It is used in analytical chemistry for the preparation of the solutions. It is either made of glass or plastic and it is usually fitted with a stopper which is made from a chemically resistant plastic such as polypropylene other than glass. Its long neck has a single ring graduation mark and a label. The label is meant to show the nominal volume, tolerance, calibration temperature, class, relevant, manufacturing standard, and the manufacturing logo.
A volumetric flask is basically characterized by having a bulb and a long neck. Although there are some with rounded bottoms, most volumetric flasks have a flattened bottom which enables them to be set onto a lab bench. A volumetric flask should be calibrated before use so as to avoid introduction of systematic errors into the measurements and also reduce the random error inherent while using the instrument.
It is important to fill the volumetric flask twice the solution that you are about to fill with. Put the stopper on the opening and shake the flask. This is important so that all the surface area inside the flask is covered. When you do this, you are sure that the solution will not be contaminated or diluted when you pour it on the volumetric flask.
Could you be wondering when it is the most appropriate time to use a plastic volumetric flask as opposed to glass flask? Well, the plastic is much needed if you need to trace analysis on analysts at ppb levels that might be lost by adsorption on the glass surface.
How to use a volumetric flask
Since there are different sizes of volumetric flasks, begin by selecting the most appropriate size for your procedure. Next, measure and add the solute for the solution. Add enough solvent to dissolve the solute. Keep adding the solvent until you get near the line marked on the volumetric flask. Fill the flask using a pipette. Ensure all liquid drain down from the sides of the flask.
Using a meniscus (a meniscus is the concave or convex liquid curve seen in the container. It takes the shape of the surface tension of the liquid and adhesions to the wall of the container) of the solution and graduation line on the flask to determine your endpoint. Finally, seal the volumetric flask, mix, swirl and ensure the solution is thoroughly mixed. You can now store the prepared solution until it is ready to be used.
The error limits of volumetric instruments according to USP
The United States authorities supervise all companies producing pharmaceuticals products by authorities such as the Food and Drug Administration (FDA) it is a must for these companies to meet the requirements of the United States Pharmacopeia. All the volumetric measuring instruments are calibrated on an individual basis.
For maximum precision, computer-controlled systems are used to ensure a fully automated production line. Another essential step is a random sampling of finished products as a statistical process control according to DIN ISO 3951.
Should you put a volumetric flask in a drying oven?
The point is, it is okay to put the volumetric flask into a drying oven but you should not take it out of the drying oven. This is because the heat would warp the glass slightly and introduce error into the calibration mark. Furthermore, this will make the volumetric flask lose its value as an accurate measuring object.
What are the advantages of using a volumetric flask?
One obvious reason is its accuracy, thus very reliable. There are several things that should make you choose a volumetric flask as opposed to Erlenmeyer. A volume flask is specially calibrated and tested ensuring the volume listed is exactly the correct volume. Another advantage is its shape which is specially designed for accurate measurements. The line to mark the correct volume and the narrow neck is equally good. The narrow neck is advantageous because the level of the water is much more sensitive to the amount of the water than the way it would if the neck was much wider.
The fact that a volumetric flask is only designed to measure one and only one volume it gives you the confidence of the results. The markings are calibrated to a more accurate degree making it possible for you to add drop by drop volume measurements of a substance, something you are not able to do with a measuring cylinder.
How to clean a volumetric flask
It is very important to clean a volumetric flask to avoid any impurities. Assuming you are in the lab, acid washing should do a great job. Remember to put on eye protectors such as goggles and gloves. Pour hydrochloric acid solution into the volumetric flask. Put on the lid and shake the flask. Turn it to make sure all surfaces of the glass inside are being cleaned by the acid. From there, thoroughly triple rinse with de-ionized water. If you are cleaning your volumetric flask at home, just pour in some white vinegar and leave it to sit there for a while. That is enough to break up anything inside the volumetric flask.
Here are some examples of volumetric flasks from foxxlifesciences.com:
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 5 mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 5mL, Borosilicate 3.3 CS/5
Specifications
- Material: 3.3 Borosilicate Glass
- Bottle Volume: 50 mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension:11.81″ L x 8.27″ W x 2.56″ H
- Class/Quality Grade: Type 1, Class A
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 10 mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 10 mL, Borosilicate 3.3 CS/5
Specifications
- Bottle Volume: 5 mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension: 11.81″ L x 8.27″ W x 2.56″ H
- Class/Quality Grade: Type 1, Class A
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 25 mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 25 mL, Borosilicate 3.3 CS/5
Specifications
- Material: 3.3 Borosilicate Glass
- Bottle Volume: 25 mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension:11.81″ L x 8.27″ W x 2.56″ H
- Class/Quality Grade: Type 1, Class A
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 50 mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 50 mL, Borosilicate 3.3 CS/10
Specifications
- Material: 3.3 Borosilicate Glass
- Bottle Volume: 50 mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension:11.81″ L x 8.27″ W x 5.12″ H
- Class/Quality Grade: Type 1, Class A
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 100mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 100 mL, Borosilicate 3.3
Specifications
- Material: 3.3 Borosilicate Glass
- Bottle Volume: 100mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension: 20.87″ L x 8.66″ W x 3.27″ H
- Class/Quality Grade: Type 1, Class A
Amber Volumetric Flask, Wide Neck, With Glass I/C Stopper, Class A with Batch certificate, 200mL
Description
Borosil Wide Mouth Volumetric Flask with Interchangeble Solid Glass Stopper, Accuracy as per Class A, ASTM Standard with Batch Certificate, 200 mL, Borosilicate 3.3 CS
Specifications
- Material: 3.3 Borosilicate Glass
- Bottle Volume: 200mL
- Color: Amber
- Tolerance: +/- 0.08
- Overall Dimension: 16.93″ L x 12.40″ W x 7.09″ H
- Class/Quality Grade: Type 1, Class A
