CAPACITIVE LIQUID LEVEL DETECTION

PRE-ELEC® compounds are key factors in accurate analyses

The accuracy of liquid handling is an essential topic for diagnostic testing. When a test is carried out, it is of paramount importance that it is trustworthy and accurate.

A single error in the liquid handling process may lead to false positives and false negatives, which may cause various problems in the subsequent steps – at worst, endangering the patients.

Sampling and liquid handling are part of the daily routine at testing laboratories, and if done manually, the chances are high for human error. Modern automatic liquid handling robots can carry out these repetitive chores as programmed, leading to higher sensitivity and specificity in diagnostic testing.

Liquid level sensing is a critical feature in automatic liquid handling. With sensitive and accurate detection of the liquid surface, it is possible to carry out high-precision pipetting of even the smallest volumes and avoid carry-over of liquids, as embedding the pipette tip into the liquid is not needed.

Liquid level sensing with conductive pipette tips

Conductive pipette tips play a key role in capacitive liquid level sensing, the predominant technology in modern automated liquid handling systems. Electrically conductive pipette tips enable the measuring of electrical signals at the pipette's tip. Conveniently, the electrical potential changes immediately and accurately as the tip comes into contact with a liquid. It reduces the need to submerge the tip into the liquid to be aspirated. Therefore, the risk of liquid carryover and cross-contamination is reduced significantly. Furthermore, the liquid handling is less dependent on having consistent liquid levels, and the need for laborious programming of the pipetting position is minimized.

To measure liquid level capacitively, the change upon the tip entering a liquid phase needs to be greater than other variances seen in the signal during tip movement. In the case of non-ionic liquids, the capacitance variation is modest, making it harder to utilize well. In these cases, the system is likely operated via pressure-sensing, an option that can also be used in parallel with capacitive liquid-level sensing. Below is an example where a tip traveling at constant speed enters the liquid. The change in capacitance is seen as a sudden shift in the baseline, while pressure takes significantly longer to stabilize and needs to penetrate deeper into the liquid.

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A tip traveling at constant speed enters the liquid. The change in capacitance is seen as a sudden shift in the baseline, while pressure takes significantly longer to stabilize, and the tip needs to penetrate deeper into the liquid.

In short, capacitive liquid level sensing provides the following advantages:

  • Not sensitive to liquid level
  • Minimal liquid contact when aspirating
  • Various control modes
Racks of pipette tips on an automated liquid handling machine in a clinical laboratory.; Shutterstock ID 571497442; purchase_order: DIAGNOSTIIKKA; job: ; client: ; other:
Racks of pipette tips on an automated liquid handling machine in a clinical laboratory.; Shutterstock ID 571497442; purchase_order: DIAGNOSTIIKKA; job: ; client: ; other:

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State-of-the-art PRE-ELEC® pipette tip materials for automated liquid handling systems​

Our electrically conductive plastic compounds are key factors in accurate analyses, where the material, mold, and process are optimized.  Read more about our pipette tip materials

Pioneering in diagnostics since 1990

We are privileged to provide materials for securing better healthcare worldwide. Premix’s electrically conductive compounds are widely used in In Vitro Diagnostics (IVD), enabling liquid-level sensing and reliable analytics in automated applications. Our conductive PRE-ELEC® compounds have been used in automated liquid handling applications since the early 1990s as the material was selected for the first liquid handling robots.

We have been trained by the high standards and tight production tolerances of the IVD technology and diagnostics industry. The requirements set for the materials have guided our strategy and technology development. We are fully committed to long-term availability and contingency preparedness.

We offer various product development and laboratory services for our customers. Our services are based on our top-notch expertise in functional plastics and carbon black know-how.

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