Laboratory glassware is the most used laboratory equipment in various laboratories. Among many glasswares, test tube is applicable in biological as well as chemical laboratories.
The test tube is a long cylindrical handheld tube shaped like a finger that has been used in various experiments. It has different types depending on the material and purpose of the experiment.
Depending on the laboratory, test tubes also have different functions; in the chemistry laboratory, the test tube helps to test the properties of various chemicals and gasses. Likewise, the microbiology laboratory uses it to prepare culture media, collect samples, and hold fluids.
Test tubes are closed at the bottom and open at the top. The bottom of most test tubes is slightly curved/spherical. The length and diameter of the test tubes vary significantly from small (Durham) tubes to large culture tubes.
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Sizes of Test Tubes
Test tubes are available in variable sizes; ranging from 10 to 20 mm wide and 50 to 200 mm in length. The standard test tube size used in laboratories is 18 mm✕150 mm.
- Extra small (Durham) tube: comes in two dimensions; 5 mm✕35 mm or 4 mm✕40 mm. It is applicable for detecting gas produced by microorganisms. These are placed upside down in order to trap the gas.
- Small tube: The dimension of the small tube is 13 mm✕100 mm, and it can hold 9 ml of materials. It is helpful in performing different types of experiments.
- Medium tube: The medium-sized tube is 16 mm✕150 mm in dimensions. It can hold approximately 22 ml of material.
- Large tube: The dimension of a large-sized tube is 20 mm✕200 mm. It can hold 28 ml of material.
Types of Test Tubes
This laboratory glassware are classified on different types on two basis; based on the material used for constructing them and based on the purpose.
Based on the material
Depending on the material used, test tubes are of two types; disposable and reusable.
- Disposable test tubes: The disposable test tubes are made of various kinds of plastics like nylon, polyethylene, polypropylene, polyurethane, polyvinyl chloride, and polytetrafluoroethylene. Surprisingly, plastic test tubes are resistant to UV light like neoprene tubes, and different temperature ranges, like test tubes made up of nitrile operable in -30℉ to 275℉. The plastic tubes made up of polyethylene are resistant to high pressure.
- Reusable test tubes: These are made of glass; borosilicate, fused silica, or quartz glass are some of the types of glass used for the test tubes. These tubes are highly resistant to temperature so autoclavable and tolerate chemicals. Although these tubes are transparent, they are more costly than disposable ones.
Other materials used in the construction of test tubes are metal and ceramic. However, using test tubes made of these materials is relatively uncommon.
Based on Purpose
Depending on the purpose, test tubes are of various types. Like thin-walled, medium-walled, thick-walled, rimmed, screw top, ground glass tops, plain tops, graduated test tubes, and some come with stoppers, push caps, and screwtops are some of the types of test tubes.
- Thin-walled test tube: It is used for storage, holding, and mixing purposes but not heating due to the risk of easy breakage. The wall thickness in the tube is generally 0.5-0.6 mm.
- Thick-walled test tube: It is used for strong heating of chemicals as the glass wall is thick. Its wall thickness is 1.5 mm.
- Rimmed test tube: The rim of the test tube helps in providing extra mechanical strength in the test tube. It helps in easy holding using a test tube holder.
- Screw top test tube: The screw top helps secure the materials inside the tube. It is usually helpful in sample collection, culture media preparation, and blood collection.
- Plain top test tube: There is no rim or screw at the top of the test tube. It is useful for holding the chemicals before and during the experiment.
- Medium-walled test tube: These tubes have a 1-1.2 mm wall thickness. It has usage in performing exothermic chemical reactions and gentle heating of materials.
- Test tube with ground glass stopper: The tube is generally useful for storing chemicals and has a ground glass top to attach the stopper.
- Graduated test tube: Like a graduated cylinder, it precisely measures samples before performing experiments. Usually, the tube has a thick wall and an interchangeable glass stopper.
Uses of Test Tubes
Test tubes have a wide range of functions depending on the laboratories. In chemical laboratories, these tubes test the substances’ properties and perform experiments in different forms between two or more chemicals. The various functions of test tubes are as follows:
- Sample collection in clinical laboratories: The collection of samples like bodily fluids (saliva, pus, and sputum) occur in clean, sterilized test tubes. It helps to efficiently transfer samples from one place to another to confirm disease diagnosis.
- Blood collection in phlebotomy: Blood collection tubes are test tubes with color-coded caps that helps in identifying the purpose of blood collection and preservatives added to the tube. Phlebotomy is a procedure of withdrawing blood from the veins placed in the blood collection tube.
- Culture media preparation in microbiological laboratories: The preparation of broth or liquid medium usually occurs in the test tube. Other biochemical mediums are also prepared in the test tube. It helps in the identification of microorganisms.
- Analysis of chemicals: In the chemistry laboratory, a test tube is useful to study chemicals. The physical and chemical properties of chemicals in various physical states (solid, liquid, and gas) are analyzed by multiple tests using the test tube.
- Disease diagnosis: The use of test tube in clinical and microbiological laboratories not only help in collecting samples and blood but also helps in disease diagnosis by performing various test, especially in culturing cancer cells and biochemistry tests.
- Holding or storing samples/chemicals: The use of some samples and chemicals may be frequent, so saving and keeping these chemicals and samples for the test and future tests is another usage of test tubes.
- Heating experiments: Different experiment requires heating of the material for mixing or accurate result like Benedict’s tests, Fehling test, etc., and the material involved is small in amount. So, using a test tube helps in performing these experiments.
Importance of Test Tubes
Test tubes, although small, are an essential piece of laboratory glassware. It is paramount in laboratories that handle risky, hazardous chemical materials, contagious samples, and growing microbial cultures. Brief description of some of the importance of test tubes are as follow:
- Helps in handling hazardous chemicals: Chemicals like acids and bases can create hazards if not handled with care. Likewise, laboratories use different chemicals that can threaten human and environmental health, so using safety measurements with safer equipment is a must. Hence, using test tubes can decrease the risk of causing accidents in the laboratory.
- Helpful in safely performing experiments: As discussed earlier, some experiments require handling hazardous material. In contrast, some may require heating, so using the test tube helps perform experiments safely. Sometimes mixing chemicals and samples in a wide-mouthed container may increase the chance of spillage, so safety guidelines suggests using smaller mouthed test tube.
- Storage and holding of samples: Some cases demand long-term storage of samples, so using test tubes for storing and holding samples is helpful.
References
- Fisher Scientific. [cited 2023Mar22]. Available from: https://www.fishersci.com/us/en/browse/90168062/test-tubes?page=1
- Test tubes information [Internet]. GlobalSpec. [cited 2023Mar22]. Available from: https://www.globalspec.com/learnmore/labware_scientific_instruments/clinical_research_labware/test_tubes
- Dimeski G, Yow KS, Brown NN. What is the most suitable blood collection tube for glucose estimation? Ann Clin Biochem. 2015 Mar;52(Pt 2):270-5. doi: 10.1177/0004563214544708. Epub 2014 Jul 7. PMID: 25002707.
- Bayot ML, Tadi P. Laboratory Tube Collection. 2022 Aug 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 32310451.
