Positive Displacement Liquid Handler

What is the Positive Displacement Liquid Handler?

A positive displacement liquid handler uses a piston in direct contact with the liquid inside a syringe. It handles volatile, viscous and detergent-like liquids accurately without tip changes, even in long unattended runs.

Overview

In positive displacement, the piston touches the liquid, so there is no air column and no dependence on tip wetting. This gives stable performance for volatile solvents, viscous liquids, detergents, oils and long runs where the same syringe dispenses many aliquots. Syringes are typically 10–5000 µL and are replaced or flushed between methods. Accuracy of about ± 1 % and precision better than 1–2 % CV is common, verified gravimetrically and photometrically under ISO 8655. Because there is no air cushion, the system is relatively insensitive to altitude and vapour pressure, which is useful for solvent-based assays and HPLC sample preparation. Carry-over is controlled by flushing or by replacing syringes, and liquid-level sensing confirms successful aspiration.

How does it work?

A liquid handler moves precise volumes of liquid by drawing them into a tip or probe and delivering them to a target vessel. In air displacement systems, a piston in the pipette or the robot moves an air column that pushes and pulls the liquid, which stays in a disposable tip. In positive displacement systems, the piston contacts the liquid directly inside a syringe, so volatile, viscous or detergent-like liquids and solvents are handled accurately. Multichannel heads aspirate 8, 96 or 384 tips at once for plate work, and nanolitre dispensers use solenoid valves, piezoelectric elements or capillary tips for very small volumes. Accuracy and precision depend on tip fit, liquid properties, temperature, wetting and aspiration speed, and are verified gravimetrically or photometrically under ISO 8655. Software defines volumes, order, mixing and wash steps, and records every action.

What are the key features?

• Piston contacts the liquid directly
• Syringe sizes 10–5000 µL
• Suitable for volatile and viscous liquids
• Accuracy about ± 1 %, precision under 2 % CV
• Insensitive to altitude and vapour pressure
• Flush or syringe replacement for carry-over

What are the technical specifications?

A typical positive displacement liquid handler configuration offers type of Positive displacement liquid handler, syringe volume of 10–5000 µL, accuracy of ± 1 % at nominal, precision of ≤ 2 % CV, liquid types of Volatile, viscous, detergent and wetted path of Syringe or disposable syringe. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Positive Displacement Liquid Handler is used in solvent handling, viscous sample transfer, detergent and surfactant dispensing and HPLC sample preparation. Across the wider Robotic Liquid Handling class, laboratories also deploy it for plate-based assay setup, compound screening and PCR and qPCR setup.

Which standards and certifications apply?

Relevant standards and methods include ISO 8655 (piston-operated volumetric apparatus), ANSI/SLAS microplate standards, IEC 61010-1 (safety requirements for electrical equipment), USP <1058> (analytical instrument qualification), 21 CFR Part 11 (electronic records and signatures) and ISO/IEC 17025 (testing and calibration laboratories). Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Verify accuracy and precision on installation and at intervals defined by your quality system, using gravimetric checks with water and photometric tests for dye solutions. Control temperature and humidity, since evaporation and viscosity change small volumes. Use the specified tips and fit them correctly, because a poor seal causes volume errors. Clean the deck, wash station and probes on schedule, and inspect for bent or blocked tips. For regulated work, restrict software access by role, retain audit trails and back up methods and data. Define carry-over limits and test them for trace work. Train operators to recognise partial dispenses, bubbles and clogs, and record all calibration, maintenance and method changes.

How do I select the right Positive Displacement Liquid Handler?

Choose positive displacement for solvents, viscous liquids, detergents and long runs where tip changes are impractical. Confirm syringe sizes and wetted materials. RFQ: liquids, viscosity, volumes, throughput and solvent compatibility. Provide the liquid list and viscosity range.

How does it compare with other Robotic Liquid Handling variants?

Match the technology to the liquid and the volume. Air displacement suits aqueous solutions where the tip is changed or washed between samples. Positive displacement suits volatile solvents, viscous liquids, detergents and long runs without tip changes, because the piston touches the liquid. Choose multichannel heads for plate-based work at 8–384 wells, and nanolitre dispensers when reagents are expensive or volumes below a microlitre are needed. Confirm accuracy and precision at the working volumes, and check compatibility with the plates, tips, tubes and reservoirs you use. Consider tip format, deck capacity, mixing and heating options, and software for method editing, audit trails and LIMS exchange. Verify carry-over performance if you run trace analysis, and confirm the service and calibration support available.