Where Results Are Only as Accurate as the Sample Amount Dispensed
From food science and the controversial GMOs, to pharmaceutical development and medical research, to the routine tests that are part of an annual checkup, liquid dispensing systems play a largely unseen (to most of us) but critical part in our everyday lives.
Whether the task at hand is an experiment in gene sequencing or antibody testing, or an analysis of blood or urine, many biotechnology and laboratory tasks begin with moving samples of a liquid between containers and dispensing a precise amount onto or into a testing medium. In the typical large setting where these processes are performed — such as a hospital running tests on 600 patients or a lab examining 10,000 samples — liquid dispensing systems are, well . . . indispensable, performing a task that would be tedious, time consuming, more expensive, and more subject to human error if performed by hand for such large-scale applications.
These liquid dispensing systems utilized in diagnostics, biotech, and research labs often depend on very small tubing — with an ID as small as 50 microns or even 100 microns (close to the size of a single human hair) — to dole out tiny amounts of liquid at high throughput. And the characteristics of the tubing can make or break the process.
What are some issues to consider when using liquid dispensing systems?
Whenever you are using liquid dispensing systems, the primary concern is knowing the exact amount of liquid being dispensed. There are many reasons why this is crucial. For example:
- You may be starting with a finite sample size and need to perform a large of number of tests. For instance, you may need to use blood drawn from a patient to perform dozens of screening procedures — and you don’t want to have to go back to the patient to draw more blood to complete the testing.
- You need to know how much of another liquid (usually a reagent) must be added to the dispensed sample in order to perform an analysis. This is because the amount of interaction in the sample is often a function of the amount of other liquid.
- Because these reagents used to perform analyses are expensive, you want to use the minimum amount necessary to achieve measurable results.
- In turn, as the machines that perform the analyses have become more sensitive, they are able to use smaller and smaller amounts of both sample and testing medium — which in turn requires liquid dispensing systems to be more precise.
Naturally, a wide range of variables can have an impact on the accuracy of the liquid dispensing systems utilized in biotechnology and laboratory automation, including the choice of instrument and the specific methodology used. But in systems that utilize small tubing for dispensing the liquid, the precision of the tubing itself plays a vital role in helping to ensure that liquid dispensing systems are accurate and the results, valid.
What role does precision tubing play in liquid dispensing systems?
Previously limited by the inability of different tubing manufacturers to attain tight tolerances — even if the tubing could be cut precisely, the ID tolerances varied too much — designers used to rely on the pumping mechanism to try to ensure the accuracy of liquid dispensing systems. In other words, if the tolerances of the tubing ID were greater than the tolerances needed to achieve a valid result, the tighter tolerances would have to be achieved despite the limitations of the tubing. However, with the improved precision and tighter tolerances of today’s tube cutting, liquid dispensing systems now depend on the combination of pumping and precision tubing for reliable performance.
Having tubing that is cut to the correct length and drawn to the desired inside and outside diameters, with a clean, burr-free ID and a properly cut end, can help to avoid accuracy issues in liquid dispensing systems. For example, as sample sizes have gotten smaller, the destination for the samples has also gotten smaller. Well plates that used to have 16 spots for depositing samples now have in the range of 1,500 very small openings in the plate surface. That means the tubing in liquid dispensing systems needs to be straight, has to be cleanly sheared, and must be properly finished at its end — for instance, flat, angled, or rounded, depending on what is being tested — so that the tubes align precisely with the very tiny wells in the test plate.
The precision of the tubing in liquid dispensing systems can also have an impact on phenomena such as wicking and the so-called last drop problem. Wicking occurs when some of the liquid sample comes up the outside of the tube rather than being dispensed into the proper destination. The “last drop problem” is where a tiny droplet of sample liquid attaches itself to the end of a dispensing tube and stays there. Both wicking and the “last drop” can lead to carryover contamination in the next testing sample.
While the commonly accepted carryover of 4 parts per billion is certainly achievable, it becomes more challenging in hospitals and other lab environments where a huge number of tests are being performed. Here, the equipment must be washed efficiently while also maintaining lab productivity and cost effectiveness.
Having the proper end cut on the tubing (flat, angled, or rounded) can help to eliminate wicking and the last drop problem, and reduce the chances of carryover contamination in liquid dispensing systems. Having tubing with a clean, burr-free ID also makes cleaning more effective and reduces ID surface roughness that can trap contaminants.
We’re not splitting hairs!
When we’re talking about liquid dispensing systems that utilize tubing that’s almost as small as a hair, it’s an understatement to say that precision matters. So, we’re not splitting hairs when we say you want the length, ID, OD, and end cut to all be as precise as possible, to help ensure that the amount of sample that is dispensed will also be as precise as can be.
Next week, we’ll take a closer look at tubing ID and other variables that can have an impact on the accuracy of liquid dispensing systems. In the meantime, to explore different precision cutting options for your metal tubing or other metal parts needs, please download our free guide, Choose with Confidence: Comparing 2-Axis Precision Cutting Methods.