Common Errors In Volumetric Dosing And Pipetting – And How To Avoid Them

Just yesterday in the lab, I was preparing dilutions for a high number of analyses. How annoying – putting the same amount of sample and solvent into each vial, once, twice, three times, many times, keeping all other details in mind to prepare identical samples. Do you remember how it was during your course of study? And that’s still the daily routine in many labs. But today automation solutions are available to ease up repetitive manual tasks and prevent volumetric dosing errors.

Do you know the main errors in volumetric dosing and pipetting?

In the daily lab routine pipetting and dosing is ubiquitous. You need to prepare numbers of dilutions for your experiments, set up standard solutions, and generate blends and mixtures of different solutions and samples. And you are used to doing that manually with samplers.

You have to ensure that each single sample is prepared in the same way without contamination and, most importantly, in the right dosing volume or dilution and mixture ratio.

Everything is routine to you and you do it automatically. But what happens if you forget a single “simple” detail like e.g. having the tip not correctly assembled to the sampler? Right, you have a volumetric dosing error – but even worse – have you recognized it in your routine handling? Most of the times you only recognize it after you have analyzed your set of samples. So you need to start everything from the beginning to receive good and reliable results and hopefully there is enough original sample left to repeat the experiment.

This is just a “simple” example of errors which could arise during pipetting or dosing, but it has a great impact on the results.

Be aware of the pipetting and dosing errors:

  • Incorrect assembled tip
  • Wrong tip
  • Unequal pipetting and dosing rhythm
  • Tilted handling
  • Temperature differences between sample and sampler
  • Density differences between sample and calibration liquid
  • Deviations in the vapor pressure between sample and calibration liquid
  • Differences in the viscosities of the sampled solutions
  • No correct moistening before dosing
  • Contaminations by using the same tip several times

All these errors could lead to deviations in the range of 0.5 % to 50 % and if several errors add up it can become even worse.

Process control, process management and minimizing inadequate handling to ensure quality

Each lab worker has to take care of quality assurance of all lab processes including sampling issues like pipetting and dosing during sample preparation to guarantee correct and reliable results. Especially for a high number of repetitive manual tasks the risk of human error is quite high. To ensure the quality and reliability of the results you need the right processes to control and manage analytical workflow steps for sample preparation.

Automation and robotics are the classical solutions for repetitive tasks with integrated control and management features of the individual workflow steps. There are a lot of automation systems for dosing issues available in the markets targeting different industry segments like chemistry, life sciences and biotechnology.

Anton Paar introduced the automatic benchtop platform for sample preparation, the Modular Sample Processor, at ACHEMA 2015.

The Modular Sample Processor is intended for automated sample preparation steps prior to analysis. As you already know, the basis for correct dilutions, end concentrations, blends and subsamples is the correct pipetting and dosing of defined volumes.

All these processes are controlled gravimetrically with a high-precision weighing unit. This unit reports directly the weight of the filling volume to the Anton Paar Control Software. The software calculates based on the defined method the correct values for subsamples, dilutions or blends to be added. So you get the correct value for your subsequent analysis and do not have to worry about volume errors.

Via the integrated bar code reader each subsample can be traced back to its original input sample/batch. This makes each subsequent measuring result traceable.

The Modular Sample Processor can be used as a stand-alone unit for sample preparation or be embedded in an individual, automated workflow. Measuring instruments such as Anton Paar viscometers, density meters, refractometers, polarimeters or any instrument equipped with a flow cell can be connected directly via the integrated media interface and/or the samples or sample trays can be quickly transported to any measuring instrument by a robot.

It provides the utmost flexibility to fit into each lab workflow and ensure process quality for sample preparation.

Modular Sample Processor by Anton PaarModular Sample Processor – a benchtop automation platform

Do not waste any more time worrying about pipetting and dosing errors – automation provides flexible solutions. Automation of the sample preparation process with the Modular Sample Processor minimizes handling errors and optimizes time efficiency. You know at any time for any sample the correct value for your subsequent analysis.

  Learn more @ Anton Paar

Show all comments (1)
  • Hi Markus
    Excellent, I enjoyed reading that. This reminds of my very first large scale solid phase chemistry where I toiled all day preparing my samples for an overnight reaction. Only to comeback the next morning to find that I had forgotten to add a reagent to kick of the reaction. I understand the focus of your article is on minimising error. If I may also add another aspect which is equally as important issue which deserves a mention. That is repetitive strain injury (RSI) which is prevalent amongst various researchers.

Add comment

Your email address will not be published. Required fields are marked *