Which of the following is an example of a TD pipette?

• A. Ostwald-Folin Pipet
• B. Volumetric Pipette
• C. Serologic Pipet
• D. Pasteur Pipet

Answer: (A)

The concept being tested is the difference between TD (to deliver) and TC (to contain) pipettes. TD pipettes are calibrated so that the amount marked is delivered, with the understanding that some liquid remains in the tip and must be blown out to obtain the exact volume.

Ostwald-Folin pipette is a classic example of a TD pipette. It is a fixed-volume, large-bore pipette designed for accurate delivery of liquids (often viscous ones). After filling to the mark, you expel the contents and perform a final blow-out to ensure the full, marked volume is delivered. This blowing-out step is the hallmark of TD pipettes.

In contrast, volumetric pipettes are designed to contain a precise volume and are typically drained without blowing out, so they are considered TC. Pasteur pipettes are simple dropper-like devices without precise calibration, and serologic (graduated) pipettes are used for delivering variable volumes with blowing out or not depending on the specific design, but they are not the classic example highlighted for the TD category in this context.