Figure 1: Universal pipet tips of similar sizes from various manufacturers.

How do you know that a pipet tip that is "universal" will fit on your pipettor? Some pipet tips cost three to four times as much as another. Does the old adage "you get what you pay for" apply? We will begin to explore the answers to these questions in this first in a series of publications. In this article, we will focus on the differences in the design and fit.

Figure 2: Two approaches to Universal Fit – Soft/Flexible hub vs. traditional hub. (Photos courtesy of Sorenson Biosciences.)

By far the most common pipet tip design which has been in use for years is the tip made from polypropylene plastic which includes all of the tips shown in Figure 1 and the tip pictured on the right in Figure 2. In order for tips with hubs made of polypropylene, the diameter of the tip hub must be slightly larger than the barrel of the pipettor and the inside taper of the tip must also match the taper of the pipet barrel. If everyone conformed their pipettor barrel design to the same standard, there would never be a problem. Unfortunately, this is not the case which leads to people wondering if their pipettor is "universal" or not and can they trust a pipet tip from anyone other than the pipettor manufacturer?

Pipettors and tips are a classic "razor / razor blade" scenario. While the pipettor can cost from $75 - $1,200 or more, this is a very small proportion of the cost of the tips that may be used on that pipettor over its useful life. This fact isn’t lost on manufacturers. Some of them go to great lengths to create proprietary barrel geometries to ensure that other manufacturer’s tips won’t fit their pipettor. And when manufacturers begin making tips to fit their proprietary design, they change the design in a never ending cycle.

In an effort to get around this problem, several tip manufacturers have begun making tips with a hub that is soft and flexible and will conform to the shape of proprietary barrel geometries. An example is shown in the photo on the left in Figure 2 which is the Sorenson Biosciences Soft Fit tip. If you have a pipettor with fit problems or one that is from a manufacturer with proprietary barrel geometries (e.g., Rainin LTS) mixed with other pipettors who can use universal tips, then this may be an excellent way to have a single, common pipet tip for your entire lab.

Fortunately, most manufacturers of hand held pipettors (we are excluding robotic pipetting stations here) make pipettors that will utilize universal tips.

So let’s look at what makes a tip Universal by first taking a look at an engineering drawing of a 200 microliter tip made by Sorenson Biosciences in Figure 3.

Figure 3: Engineering drawing of the Sorenson Biosciences Standardization 200 microliter yellow pipet tip. (Measurements shown are in inches.)

One thing you will note is the inside diameter of 0.213 inches (5.41 millimeters.) Within very tight tolerances, this is the same diameter for every tip pictured in Figure 1. Although we have no way of accurately measuring the taper, suffice to say that these tips have tapers that are similar enough that they fit perfectly on a variety of pipettor brands that advertise accepting universal tips.

That’s exactly what this means! Don’t be fooled by all of the differences in the hub shoulder designs. In spite of the wide variation shown in Figure 1, all of these tips fit on and eject off a universal pipettor with equal ease. So what this means is that you have a whole lot more choices than you may have thought! If you are afraid to try a different tip for fear it won’t fit properly, you may be pouring money down the drain by buying the same brand tip as your pipettor!

Shop around on our site for tips that fit your pipettor! Our results will allow you to make your choice based on other criteria such as cost and packaging which we will explore in depth in another article.