Home » Products » Analytical Solutions » Pipettes & Liquid Handling » Mettler Toledo Pos-D Positive Displacement Pipettes
Pos-D Pipettes
|
For high densities, viscosities, or vapor pressures.
Mettler Toledo Pos-D Positive Displacement Pipettes
The Rainin Pos-D from Mettler Toledo is a specialized positive-displacement pipette engineered to handle problematic liquids that air-displacement pipettes cannot process accurately. Technically, the Pos-D utilizes a disposable capillary and piston (CP) assembly where the piston comes into direct contact with the liquid.
This design eliminates the air cushion between the sample and the piston, preventing errors caused by liquid physical properties such as high density, high viscosity, or high vapor pressure. This makes the Pos-D an essential technical tool for molecular biology, forensic science, and clinical chemistry where absolute sample integrity and volumetric precision are non-negotiable.
The Positive Displacement Mechanical Principle
The Pos-D is technically distinguished by its positive displacement mechanism, which differs fundamentally from standard air-displacement systems. In this setup, the piston is part of the disposable tip and makes direct contact with the sample. By removing the air gap that typically sits between the piston and the liquid, the Pos-D eliminates the "elasticity" of an air cushion. This ensures that the exact volume set on the pipette is the exact volume aspirated, regardless of the liquid's viscosity or temperature-driven expansion.
Specialized Handling for Viscous and Dense Liquids
Handling liquids like glycerol, fats, resins, or high-density buffers is a major technical challenge for conventional pipettes due to their resistance to flow. The Pos-D addresses this through the direct mechanical action of the piston within the capillary. The piston effectively "wipes" the walls of the capillary during dispensing, ensuring that even the most tenacious and viscous liquids are fully expelled. This results in high accuracy and reproducibility for complex chemical and biological formulations that would otherwise stick to the inside of a standard pipette tip.
Precision with Volatile and High-Vapor-Pressure Fluids
Volatile solvents such as acetone, ethanol, or hexane tend to evaporate into the air cushion of standard pipettes, causing leaking and inaccurate volumes. Technically, the Pos-D's direct-contact design prevents this evaporation because there is no air space for the vapor to expand into. This makes it the preferred tool for labs working with organic chemistry or environmental samples, as it provides a stable and leak-free environment for transferring liquids with high vapor pressures.
Absolute Contamination and Aerosol Prevention
For sensitive applications like PCR, DNA sequencing, or forensic analysis, cross-contamination is a critical failure point. The Pos-D technically prevents aerosol formation because the sample is completely contained within the disposable capillary-piston (CP) unit. Since no part of the pipette’s internal shaft ever comes into contact with the liquid or its vapors, there is no risk of carry-over between samples. This "built-in" protection ensures the purity of the experiment without requiring specialized filtered tips.
Ergonomic Design and Pre-Assembled CP Tips
Despite its robust mechanical action, the Pos-D is engineered with a focus on operator comfort. The pipette features an ergonomic handle with a finger hook that allows for a relaxed grip during long sampling sessions. To further streamline the technical workflow, the capillary-piston units are available in pre-assembled racks. This "web-style" packaging allows for the quick and easy loading of the CP onto the pipette without manual assembly, reducing the risk of contamination and increasing lab throughput.
High-Visibility Volume Display and Precise Adjustment
The Pos-D features a clear, high-contrast digital display that ensures the set volume is easily readable. Technically, the volume adjustment mechanism is designed for smooth operation while maintaining a secure lock to prevent accidental changes during pipetting. This ensures that the volumetric precision remains constant across multiple cycles, which is vital for preparing standard curves or executing complex clinical protocols where volume drift could compromise the results.
Durability and Chemical Resistance of Materials
The technical construction of the Pos-D incorporates high-grade materials selected for their durability and resistance to harsh laboratory environments. The pipette body is designed to withstand frequent use and exposure to a variety of chemical vapors. The disposable CP units are made from high-quality polymers that do not interact with the samples, ensuring that the chemical profile of the liquid remains unchanged during the transfer process.
Versatility Across Clinical and Research Applications
The Pos-D is a versatile technical instrument capable of supporting a wide range of laboratory disciplines. From handling viscous oils in industrial quality control to transferring sensitive blood and serum samples in clinical diagnostics, its mechanical reliability makes it a universal solution for "difficult" liquids. The ability to switch between different volume models ensures that the lab can maintain the same high level of accuracy from microliter to milliliter ranges.
Click here for more information about Mettler Toledo range of products
