This description I felt was the first true engineering practice, where I deconstructed a laboratory pipette.

I Introduction:

Precision in scientific experiments is crucial, and even the smallest miscalculations can throw off weeks, months, and even years’ worth of research. To make sure that scientists are always obtaining the proper amount of fluids, acids, and solutions they desire for their experiment, the pipette has been what is used for these exact measurements. A handheld device that allows experiments to go as smoothly as possible, permitting scientists to continue pushing the limits of breakthroughs. The origins of the pipette started with a man called Francois Descroizilles who had developed the berthollimetre and alcalimetere. These inventions were 

viewed as “early precursors to the buret and pipette, respectively,” later to be further developed by Joseph-Louis Gay Lussac. (Wright 2014) 

Figure 1. Descroizilles’ polymère chimique- which included both the berthollimetre and alcalimetre. Source: Duval, C. (1951). J. Chem. Educ., 28(10).

Lussac’s work in 1824 would continue to be the norm with some slight changes throughout the years, until when it appears scientific methods turned backward, as labs began mouth pipetting. Lab technicians would be using straws with measuring labels on them to pull out a certain amount of fluid. This obviously leads to many health hazards, as the ingestion of volatile chemicals and substances couldn’t be avoided. 

This would lead to the frustration of someone called Heinrich Schnitger, who in 1961 after being frustrated with mouth pipetting patented the fixed volume “piston-driven” pipette known as the Marburg pipette which can still be seen today. (Wright 2014) In 1974, however, Warren Gilson and Henry Lardy, known as the Gilson model, patented a pipette with adjustable volume control. (Wright 2014) Many would argue whether the Gilson model stole from the Marburg pipette, but nowadays pipettes are a combination of the two. Usually, they are referenced as micropipettes and both ushered in a proper safe method to accurately carry out future scientific experiments. 

II Body:

To deconstruct the pipette, I’ve chosen to follow the diagrams provided for the schematics of publically available ones and other descriptions that are available online. For this specific technical description, I’ve chosen to use a mechanical air displacement micropipette, which pulls in quantities of substances through a growing and shrinking air pocket within the pipette. (Microlit 2021) It is also only a single-channel pipette, being able to hold one amount of liquid at a time before having to be dispensed. As the pipette works by the presence and lack of pressure on the pipette itself, the device works through a series of actions going from top to bottom. Thus, I feel it is appropriate to follow this order when looking at the pieces which make up the device. 

Figure 3. Micropipette Core Diagram featuring dual-purpose plunger button. Source: Microlit USA, Micropipette Product Diagram, 2021.

II A Top:

Starting at the highest point would be the plunger button and the plunger shaft, the area overall is referenced as the plunger. The plunger button can either be used for one purpose or two. The larger shared purpose between pipette devices is to be the point at which the operator uses the pipette. The usual order to press and pull the plunger is to insert the pipette into the desired fluid and pull the plunger up the plunger shaft to create a suction in order to obtain your set quantity. (Microlit 2021) Then, you’ll remove your pipette and transfer it to your second location, where you will press the plunger shaft down to release the substance. Thus, the plunger section’s main goal is to be the main point of contact to properly use the desired pipette, allowing the scientist to collect and obtain materials. 

Considering how hazardous some materials in a lab can be, it is general practice never to mix any materials in the fear of contamination. Thus, every time one pipette job is finished, the tip is removed, for another one to be suctioned onto the end. This job is done through a button usually behind the plunger section, called the tip ejector. The button is found at a lower level than the plunger button itself. Interestingly, its spot is near where the plunge button rests when fully depressed, allowing for quick access after the main goal of the pipette is fulfilled. (Microlit 2021) These 3 components make up the top section of the pipette and largely contain the operator’s contact points for the device. This, however, can change depending on whether the plunger button is given a second purpose. 

Figure 4. Extended diagram of a Gilson Pipetman-style pipette with volume adjustment knob. Source: Tek-Pette Pipette Diagram.

II B Middle:

 The second purpose the plunger button can have is also to be in charge of volume adjustment, in which case it is normally seen with ridges along the circumference to provide a more defined texture to the user. Through this, a scientist is able to quickly control the amount of fluid they are obtaining. In some other models, however, the role of volume adjustment is delegated to a knob in the larger part of the pipette called the body, which is the larger plastic casing of the later mechanisms. This knob is found directly after a plastic separation indicating the end of the plunger and the start of the body and performs the same purpose of volume adjustment. (Tek-Pette 2022) This can be seen as having its advantages even if it is arguably a bit harder to reach, given that it is separated from the press/depress mechanism of the plunger, the operator is less likely to make a mistake when using the pipette. This could be in the form of accidentally changing the amount of liquid being pipetted midway through its usage. Also found in the body rather recently would be a digital volume indicator, allowing the users to gain the most precise measurement of exactly how much they are going to be using in their lab experiments. (Microlit 2021) 

II C Bottom: 

Moving past the body is the tube where the liquid is stored, called the shaft. The first item within the shaft is the piston itself, consisting of a large spring on top and a small spring on the bottom, with two positioners to connect one another. A disposable filter is also present to prevent any contamination of the micropipette for any further usage, followed by a poly-seal o-ring for further separation. (Tek-Pette 2022) Going down the shaft is the “sealing end” that creates a gap between the shaft and the final portion of the pipette, the disposable tip, and connected to it the tip-ejector arm. (Tek Pette 2022) The disposable tip is something already discussed when explaining the usage of the plunger button, but its separation mechanically from the shaft also is a way in which the pipette can avoid becoming contaminated, allowing the operator to follow standard procedure. The arm connects the body and right above the tip itself, finishing at the sealing end. (Tek Pette 2022) Thus, it operates by releasing the disposable tip whenever the tip ejector is pressed, and releasing it whenever the button is depressed.

Conclusion:

Being that I hope to one day work in a laboratory setting, breaking down the pipette allowed me to further understand what role each mechanism played in fulfilling its purpose. Furthermore, I was able to see how the manufacturers have designed their pipettes with different opinions on how to balance practicality, and error reduction to engineer the best product possible. 

Works Cited

Pipette Diagram. (n.d.). Tek-Pette Pipette Calibration & Repair. Accessed October 29, 2022, from http://www.tek-pette.com/pipette-diagram

What is a Micropipette, How to use a Micropipette, Pipetting Technique, Function & Uses, Positive Displacement Pipette. (2021, January 20). Microlit. Accessed October 29, 2022, from https://www.microlit.us/micropipette-product-guide/

Wright, Meredith. Origins of the Pipette: Why Today’s Scientists Don’t Need to Use Their Mouths. (2014, March 31).The Incubator.  Accessed October 29, 2022, from https://incubator.rockefeller.edu/origins-of-the-pipette-why-todays-scientists-dont-need-to-use-their-mouths/