Wondering how filter tips fit between brands? Well you've come to the right place. In the last article we talked about how unfiltered tips fit on universal pipettes. The same rules apply here there are only 3 tip sizes 3.8mm, 6.1mm and 7.4mm. All filter tips are the same diameter, they differ in where the filter is placed in the tip.
First some terminology...
Collar - The part of the pipette tip that fits onto the pipette. The diameter of the collar is what determines tip fit. Universal tips are only 3 sizes, determined by the collar diameter. 3.8mm, 6.1mm or 7.4mm
Pipette Shaft - The part of the pipette that the tips fit onto. The diameter of the shaft is what determines tip fit. Depending on the volume of the pipette, the shaft may have a more or less tapered shape that determines how far it goes into the tip.
Why do pipettes have different length shafts with different tapers? It comes down to drag. Universal pipettes are also called air-displacement pipettes. They displace air of a known volume and create a small amount of suction to move a calibrated amount of liquid, essentially precision turkey basters. Anyways, the further they get from the sample, the more drag the air inside the tip experiences and the less precise they become. Have you ever tried to blow out a candle? From 6 inches it's easy, right? From 10 feet away it's almost impossible. That's because the air you are blowing is experiencing drag.
Air displacement pipettes a.k.a. universal pipettes, experience the same thing. To solve for this pipette designers make the shaft of the pipette longer so it gets closer to the sample inside the tip. A 20uL pipette has the longest shaft of any model as there is the most dead air volume inside the tip and needs to go further to reach the sample. A 100uL is shorter and a 200uL the shortest yet.
So while 200uL tips may all be the same 6.1mm diameter, the filter is moved higher or lower inside the tip to accommodate the different shaft length. Below is a picture of a 20uL, 100uL and 200uL filter tip (from left to right). The 20uL filter is the lowest, then the 100uL higher, then 200uL the highest.
So with this in mind universal tip fit is actually not too hard.
10uL filter tips - This ones easy, any size under 10uL 1uL/2uL/5uL/10uL use the same 3.4mm wide filter tip. An example is Nest Scientific 10uL tip part number 311012.
20uL pipettes that use extra long 10uL tips - These are pipettes with a 3.4mm wide shaft that use a 10uL tip that is extra long and holds 20uL total. Usually pipettes that use this kind of tip are grey accented in their color scheme or multi-channel. An example is Nest Scientific extra long 10uL tip part number 314012
20uL filter tips - These are 6.1mm wide but for 20uL pipettes. Most 20uL single channel pipettes use this type of 20uL filter tip. They also tend to have yellow color schemes, like yellow plunger buttons, design accents etc.. An example is Nest Scientific 20uL tip part number 315012.
100uL filter tips - These are 6.1mm wide but for 100uL pipettes with the filter midway up inside the tip. An example is Nest Scientific 100uL tip part number 316012.
200uL filter tips - These are 6.1mm wide but for 200uL pipettes, with the filter nearest to the collar of the pipette. An example is Nest Scientific 200uL part number 312012.
300uL filter tips - These are 6.1mm wide but the tip is extra long to hold an extra 100uL of sample. These are essentially extra long 200uL tips. The filter is in the same position as a 200uL filter tip. You can use 300uL filter tips on 200uL pipettes. An example is Nest Scientific 10uL tip part number. An example is Nest Scientific 300uL part number 319012.
1000uL filter tips - These are 7.4mm wide. They fit only 1000uL pipettes. An example is Nest Scientific 1000uL filter tip part number 313012.
1250uL filter tips - These are 7.4mm wide extra long 1000uL tips to hold an extra 250uL for 1200uL pipettes. These are usually for multichannel pipettes as 1200uL is a volume only seen on 8 and 12 channel pipettes. These can be used on single channel 1000uL pipettes as well as they are extra long 1000uL tips. An example is Nest Scientific 1250uL tip 317012.
Not sure about all this filter tip fit business yet? Drop us a line and we will get you sorted out and send some free samples.
Curious about tip fit on other types of pipettes? Check out these articles on Rainin LTS tip fit and special case tip fit.