In analytical labs, volumetric precision is not optional. Whether you’re diluting buffer for an HPLC run or transferring titrants, errors as small as 0.1 mL can lead to variability. Among essential glassware, graduated pipettes, especially Mohr pipettes, serve a key role where partial delivery and precise control are needed.
This blog talks about proper use techniques, pre-use checks, and integration with lab workflows. Product references are based on Mohr pipettes from Borosil Scientific, including Class A and Class B options with and without calibration certificates.
Understanding Graduated Pipettes: Mohr vs. Serological
Graduated pipettes allow flexible volume transfer. Mohr pipettes are calibrated “to deliver” (TD), with graduation marks starting above the tip. Serological pipettes, by contrast, are calibrated to include the tip volume.
| Pipette Type | Graduation Type | Volume Calibration | Ideal Application |
| Mohr Pipette | Partial | TD (to deliver) | Stepwise transfers, buffer aliquoting |
| Serological Pipette | Full-length | Blowout | Reagent preparation, media transfers |
Mohr Pipette Range
Mohr pipettes are widely used in settings that require accurate delivery of varying volumes, especially in titrations, dilutions, and buffer transfers. Companies like Borosil Scientific offer an extensive portfolio of Mohr pipettes, designed for high clarity, repeatable accuracy, and operational durability. Each pipette is calibrated to deliver (TD), suitable for incremental dispensing.
The range includes both Class A and Class B options, giving labs the flexibility to choose based on precision requirements. Class A pipettes are recommended for regulated environments requiring traceable calibration data, while Class B models serve well in day-to-day laboratory routines where slightly broader tolerances are acceptable.
All pipettes are designed to withstand thermal changes, resist chemical corrosion, and maintain graduation visibility through repeated autoclaving or acid exposure.
Pre-Use Inspection and Preparation
Before drawing any liquid, make sure the pipette is physically intact and properly cleaned. These steps are foundational to maintaining volumetric accuracy in pipetting.
- Check for cracks: Inspect the bore and tip under lab lighting.
- Ensure cleanliness: Rinse with deionised water to remove surfactants.
- Verify calibration: Use pipettes with valid COA or recalibrate with the gravimetric method.
- Select an optimal volume range: Choose a pipette that allows measurement within 30-90% of its range.
Using Mohr Pipettes: Step-by-Step Technique
To achieve consistent and accurate measurements, follow this standardised pipetting approach. The following steps align with best practices used in regulated laboratory environments.
- Attach pipette controller: Use a mechanical controller or bulb. Mouth pipetting is not permitted.
- Immerse the tip 1-2 cm below the liquid surface.
- Draw liquid above the zero mark, then release until the meniscus aligns exactly with zero.
- Deliver volume by allowing liquid to fall under gravity to the desired graduation. Do not blow out residual tip volume.
- Read at eye level: The lowest point of the meniscus must align with the calibration mark.
Mohr pipettes do not include the tip in volume measurement. Do not invert or blow out unless specified.
Application-Based Selection
Different laboratory applications demand specific levels of precision, readability, and certification. Choosing the appropriate pipette for the task provides consistent outcomes and better alignment with procedural requirements. Below is a table highlighting product recommendations based on use cases.
| Task | Suggested Product | Reason |
| HPLC buffer preparation | 7059 – Class A, calibrated | For traceable measurements |
| GC diluent transfer | 7062 – White markings | Easy readability against solvents |
| Titrant dispensing | 2030 – NABL certified | Precision delivery without overfill |
| General solution handling | 7060 – Class B | Economical and sufficient for daily work |
For HPLC vials, reproducible volumes from Mohr pipettes help maintain injection volume consistency.
Dos and Don’ts of Using Graduated Pipettes
A pipette’s performance isn’t only about build quality; it’s also about technique. Following best practices helps reduce human error and maintain consistency, especially during routine workflows.
Do:
- Calibrate regularly for Class A applications
- Use gloves to avoid body heat influencing readings
- Maintain vertical orientation during both aspiration and dispensing
Don’t:
- Tilt the pipette while reading
- Use plastic pipettes for strong organic solvents
- Force remaining liquid from Mohr pipettes unless specified
Storage and Cleaning
Proper storage and cleaning not only extend the life of the pipette but also ensure accuracy in repeat use. Make sure your post-use routines follow the standard lab protocols.
| Activity | Recommended Practice |
| Cleaning after acidic use | Rinse with tap water, then with distilled water |
| Protein/biological residue | Use chromic acid if SOP allows; rinse thoroughly |
| Storage | Upright in a pipette stand or a padded drawer, no bulb attached |
Avoid drying in vertical ovens above 60 °C, which can warp graduation visibility.
Class A vs Class B: When to Use Which
Understanding tolerance levels is critical when selecting pipettes for regulated environments versus routine use.
| Class | Tolerance (10 mL) | Use Case |
| A | ±0.02 mL | Analytical chemistry, regulatory reporting |
| B | ±0.10 mL | QC checks, non-critical volume transfers |
Where method reproducibility or COA generation is involved, only Class A pipettes (2030, 7059) from premium suppliers like Borosil Scientific should be used.
Conclusion:
In regulated and high-precision environments, graduated pipettes remain critical tools for exact volume handling. When used correctly, Mohr pipettes support applications ranging from stepwise dilutions to sample prep for HPLC vials or GC analysis.
By selecting borosilicate Class A instruments from Borosil Scientific, backed by NABL certification and calibration documentation, labs can maintain process integrity and audit readiness.
For labs developing SOPs or evaluating volume transfer reliability, refer to companies like Borosil Scientific e-Catalogue or connect with our product specialists for workflow-specific recommendations.
Because reproducibility starts at the bench, with the proper glassware.
