7 Different Types of Chemistry Flasks and Their Uses
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Chemistry labs are filled with a variety of specialized equipment you're unlikely to find anywhere else, such as glassware, stirrers, microscopes, and testing kits. Within the glassware category, there are several types of flasks in chemistry that are utilized in a laboratory environment. Each of these flasks is created for a specific function, and is designed to withstand the conditions this function may subject it to. In this article we will explore the 7 different types of science flasks you will find in a chemistry lab. We will explain the purpose each of these containers serve in the lab, and go over the reasons behind their designs - from their shapes and volumes to the materials of which they are made.
Besides the role your flask needs to fill, another important thing to consider when searching for chemistry lab flasks is their status with the American Society for Testing and Materials (ASTM). The ASTM is an organization that sets standards for, among other things, equipment used in chemical science. Although the ASTM is not held responsible for forcing compliance with these standards, they are held in high regard in the chemical science industry on a global scale. Further, a certification earned from the ASTM can position glassware manufacturers and retailers as leaders in their respective industries, since it verifies that they produce products of the highest quality.
Otherwise known as a conical or titration flask, an Erlenmeyer flask has a flat base, cone-shaped body, and a cylindrical neck. The tapered, bulbous bottom of the Erlenmeyer flask coupled with its slim, long neck makes it ideal for swirling liquids without the danger of spilling. Other uses for this glassware include boiling, cooling, filtering, incubating, and storing liquids. Although Erlenmeyer flasks are typically stamped with volumetric measure marks, they are not recommended to measure volume. Erlenmeyer flasks can come in a range of sizes and are usually made of glass or plastic. They may also come equipped with caps for further safety in storing or mixing. The Erlenmeyer flask is named after its creator, a German chemist named Emil Erlenmeyer.
Büchner flasks are also known as Bunsen flasks, vacuum flasks, side-arm flasks, filter flasks, or suction flasks. The Büchner flask is a version of the Erlenmeyer flask that is made with thicker, heavier walls. The purpose of the thickened walls is to allow it to withstand a higher amount of internal pressure than a regular Erlenmeyer flask can.
Like an Erlenmeyer flask, a Büchner flask has a flat base, cone-shaped body, and cylindrical neck, but its neck is shorter and has a small tube protruding horizontally out of it. This tube is used to connect to a vacuum source to create pressure during filtration. Due to the nature of their applications, Büchner flasks are typically made of glass. Büchner flasks are named after Ernst Büchner, a German industrial chemist.
As their name implies, boiling flasks are used for heating or boiling liquids. Because they must tolerate such high thermal and chemical stress, these chemistry lab flasks are most commonly made of borosilicate glass. Boiling flasks have long necks and rounded bodies with either flat or rounded bottoms. This design is ideal for heating and boiling liquids because it promotes even heat disbursement with minimal evaporation. Boiling flasks were created by Otto Schott, a German chemist who also invented the borosilicate glass that boiling flasks are made out of.
Reagent flasks are chemistry laboratory containers used for storing liquids or powders. They can be made of plastic, glass, or borosilicate glass and can be tinted green, blue, red, or brown to shield any chemicals that may react negatively to light or radiation. Reagent flasks come equipped with a stopper or cap to contain the chemicals they are storing. These stoppers are manufactured just as carefully as the flasks themselves and must be mindfully chosen depending on the contents of each reagent flask. With regards to their name, "reagent" is a word used to identify matter used in a chemical reaction.
Although they can come in a variety of shapes, volumetric flasks are ideal for measuring a substance or chemical solution with precision. Volumetric flasks have a graduated neck for measuring chemicals accurately. They can either be tube-like all the way to their base as shown in the image above, or have a pear-shaped body with a flat bottom. Also called graduated flasks or measuring flasks, these science flasks are graded as either Class A (or Class 1) or Class B (or Class 2). Class A volumetric flasks are better for use in an analytic laboratory setting, as they are more precise and made from more durable materials.
Round bottom flasks have round bodies and round bottoms. They are able to rest upright on a flat surface with the help of either stabilizing rings that the bottom of the flask rests within, or stand clamps secured to their necks. Similar to boiling flasks, round bottom flasks are ideally designed for boiling and distilling liquids. Round bottom flasks can have either wide or narrow necks that can be short or long depending on their contents and applications. Emil Erlenmeyer, the German chemist who created the Erlenmeyer flask, also created the round bottom flask. Because of the thermal shock they must endure during heating and distillation, round bottom flasks are normally made of heat-resistant borosilicate glass.
Distillation flasks, also known as fractioning flasks, are chemistry flasks used in the process of heating liquids for distillation. Distillation involves dividing liquids within a mixture by boiling and evaporating them, thus creating condensation that escapes out of the tubular arm protruding out of the neck. With its round bottom and long neck, the design of the distillation flask is perfect for this application. Distillation flasks are made of borosilicate glass to withstand the high temperatures required to distill liquids.
It should be noted that although some of these flasks can be fabricated out of plastic, glass is really the ideal material due to its ability to withstand high temperatures and the corrosive chemicals that are frequently used in a laboratory setting. For the best selection of high-quality, ASTM-compliant laboratory glassware, visit the AmScope product page today.
Simple actions can make a lot of difference to the outcome of your shake flasks cultures. Some beneficial ones have been covered in a previous post 5 Ways to Increase Biomass in Your Shake Flasks . However, common practices can also be a barrier to effective optimization.
These include:
Overfill
ing
your flasks
Keep opening the
incubation chamber
door to sample
,
feed or add new flasks
Using
a thermometer
taped
to the glass of the chamber door
Pack things around the
outside of the incubator
shaker
This short overview will explain why these things count as sins against your shake flask culture and what you can do to overcome them.
Overfilling shake flasks
The usual filling volume for standard Erlenmeyer flasks is 20 % of total volume e.g. a 250 mL shake flask will contain 100 mL of culture. This is already above the fill volume which produces better oxygen transfer (10-15 %). Specially designed high-density culture flasks are an exception to this general rule. To fill beyond 25 % will both handicap growth of aerobic cultures and can increase wear on shaker bearings by raising the height of the load.
The aim of shaking using an Erlenmeyer flask is to provide good mixing and increase the surface area for oxygen transfer. A smaller volume can be partially distributed over the side wall of the flasks by the shaking action. If the fill volume is too large, a large proportion of the culture will not move from the centre of the flask, leaving a deeper liquid level and a smaller surface area for gas transfer.
For large flasks, this extra volume also has the effect of raising the height of the load on the shaker platform. This can significantly alter the optimum shaking parameters, as the forces applied varies according to the square of the height i.e. double the height and the maximum weight or speed possible will be reduced to one forth. Avoiding overfilling is better for both the culture growth and the shaking mechanism.
For any temperature control system to work effectively, there must be a differential between the room temperature and the minimum control temperature. If cooling is not available, the only action for a temperature controller is to turn off the heating if the actual value exceeds the set point.
The effect on the shake flask culture can be dramatic. For mammalian cells, just a single degree overtemperature can be enough to either kill the cells or, at least, severely reduce viability and growth. This makes the absolute minimum temperature for an incubator shaker without cooling approximately 30 °C, if a guaranteed room temperature of 20-22 °C can be achieved in all circumstances.
This is already too high for insect cell cultures and borderline for some yeasts. Ambient temperatures of 30 °C+ in Summer are almost certain in many parts of the world. Cooling is practically a standard for all but thermophilic cultures unless the laboratory has a very efficient air conditioning system. Cooling just the incubation chamber will be both more efficient and less expensive.
Frequent door opening
The need to open the incubation chamber door for sampling, feeding or exchange of flasks has the following effects:
Temperature control will stop, with fans switching off to help maintain the chamber temperature
The shaking will stop, with a gentle slow-down taking some seconds
Access to the flasks is necessary, the door will remain open for seconds or even minutes
When the operations are
finished
, the door
must
be closed, the shaker gently re-starts and the tempera
t
ure control switches on again
Total up the time when the culture is not at the correct temperature and shaking speed and compare this to the total duration of the culture. For short cultures e.g. 12 hours or less, this can be significant.
This is very unlikely to kill your culture, but it is likely to affect:
Growth and viability due to sub-optimal mixing and oxygen transfer
Time to reach a specific biomass level for e.g. adding
inductant
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Statistical validity of replicates e.g. do the flasks nearest the chamber door get cooler?
One answer to this problem is to add options to your shake flasks, so that biomass estimation and even simple feeding can be achieved automatically without opening the chamber door. The issue of adding and removing flasks can be due to common usage. If the incubator shaker is used by multiple groups, each one will add and remove flasks at different times. This can lead to a significant amount of time when the cultures are not at the correct temperature and growth suffers for all users. This issue can be solved by booking sole use of an incubator shaker. If this is leading to large units containing just a few flasks, it may be more efficient to consider having more small incubator shakers available.
Taping a reference thermometer to the incubation chamber door
Taping a reference thermometer to the clear window of an incubator shaker is not a “sin” in itself, but believing the value certainly is. The key point is that the reading is NOT the temperature of the incubation chamber. It’s an amalgam of the temperature of the air inside the chamber reaching the door and the seepage of ambient temperature through the clear panel.
Believing this reading is accurate can lead to a decision to change the control value by a degree or more to make the thermometer reading match the desired growth temperature. This is simply wrong when you consider the temperature which matters is a centimetre or two above the shaker tray where the culture is located. The temperature sensor used as a reference for control is located in the main air stream and closer to the shaking platform.
For the ultimate accuracy, an optional external temperature sensor mounted in a flask on the shaking platform can be used. This must be filled to a similar volume as the growth flasks and located in a good position to ensure the maximum stability of the reading. However, the greatest benefit will be achieved by just taking the supposed reference thermometer off the chamber window.
Pack items around the incubator shaker
This is something that can happen over time with no obvious reason why it could be harmful.
An incubator shaker depends on a good airflow around it on all sides for:
Drawing fresh, oxygenate air into the incubation chamber
Removing excessive heat from the chamber
Cooling of electrical components e.g. a cooling compressor
However, this clearance may be considered as a good place to store boxes, packing, or even further reduced by moving the incubator shaker nearer to a wall. This will result in components running hotter than indented, reduced movement of air through the chamber and a source of clutter interfering with good cleaning.
The answer is simple: Please be guided by the manufacturer’s instructions on clearance and ensure anything finding its way into this space is removed promptly.
As air is exchanged between the head space above the shake flask culture and the main incubation chamber, it is inevitable that some moisture will be lost at temperatures above ambient. For a short culture with large volumes, this may be insignificant. However, if a small culture volume is used with a culture of long duration, changes in the concentration of solutes and osmolarity can interfere with growth. This is especially true for mammalian cell cultures.
Evaporation can result in growth limitations and reduced productivity due to many factors, including:
As an aside, this is even more apparent when micro-well plates are cultured, as the volumes are much lower at the outset. For plates, a box with reduced ventilation may be used to reduce evaporation losses. In some cases, special covers over each plate which allow gas exchange can also help prevent moisture loss.
The “catch all” solution in this case is to specify a humidification system for the incubator shaker. This can use ultrasonics for aerosol creation from a bath inside the chamber, or a small steam generator can directly inject steam. An advantage of the latter system is that it removes a potential place for contaminants to grow i.e. the water bath. For a comprehensive overview on the different humidification systems available on the market have a look at our blog post Preventing Evaporation: Humidification Systems in the Incubator Shakers.
Contamination of the incubation chamber is a serious risk, which can be hard to remove once it is established. This can be caused by spillages getting below the shaker platform, where they may be hard to reach and clean up. A flask breakage is the most likely cause in this case. However, smaller spills caused by rough handling or transfer on the outside of flasks can lead to problems over time.
Rather than let this situation progress until full disinfection and/or sterilization is required, a prompt reaction to spillages and a regular cleaning schedule can stop the problem before it starts. If the incubator shaker is a shared resource, this could be organized on a rota schedule, so no single operator must do this task very often. Our blog post “How to Clean Your Incubator Shaker” guides you through all the essential cleaning steps.
A best practise routine can be added to any SOPs for general cleaning:
Cleaning surrounding areas
should be
designated to a person, group or contractor
A schedule should be agreed regarding
frequency and thoroughness of the cleaning process
A log should be kept detailing
results of
earlier
u
ntreated spillages
Good design can help! A shaker platform which can be easily moved for access beneath is a real benefit. A smooth chamber base with rounded corners and a drain point will allow for vigorous rinsing out of serious spills. Options such as an anti-microbial coating or UV sterilization of the air stream can then deal with the much lower levels of potential contaminants which can enter from the laboratory environment.
Conclusion: T
he issues reviewed are all easy to correct!
With some foresight and an appreciation of why they are problematic, avoiding these mistakes is simple. In addition, most solutions are cost-free or inexpensive:
Only fill flasks to maximum 20
% of total volume
.
Ensure an adequate differential with room temperature for good control or actively cool
.
Minimize door opening during cultivation
.
Don’t use a thermometer taped to the chamber window
.
Keep the area around the incubator shaker clear of obstructions to air flow
.
Be aware of the potential for evaporation losses over time and plan for this
.
Institute a regular cleaning regime and deal with spills right away.
Avoid the “7 deadly sins” and your cultures will be pure and productive.
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