The Volumetric Pipet and Pipetting Technique

Learn that volumetric pipets are calibrated glass or plastic tubes (1-100 ml) designed for accurate liquid measurements. Identify the specifications imprinted on the pipet, including the volume, calibration temperature, and whether it is a TD (to deliver) or TC (to contain) pipet.

Examine the pipet for cleanliness by checking that water does not bead up on the inner surface. If the pipet is not clean, follow a cleaning procedure or obtain a clean pipet.

Pour the liquid to be pipetted into a beaker, ensuring sufficient volume is available. Using a pipet bulb, draw up small quantities of the solution and rinse the entire interior surface by rolling the pipet horizontally with a rocking motion, repeating at least three times total.

Using the pipet bulb, fill the pipet with solution until it reaches 2-3 cm above the graduation mark. Remove the bulb and immediately place your forefinger over the top of the pipet stem, ensuring no air bubbles or foam are present.

Tilt the pipet slightly and wipe the outside lower stem with lint-free tissue to remove adhering liquid. Hold the pipet vertically over a waste vessel and slowly decrease finger pressure to allow the liquid level to drop until the bottom of the meniscus aligns exactly with the graduation mark.

Move the pipet vertically to the receiving vessel with the tip touching the wall. Allow the sample to drain freely, then wait an additional 5 seconds by counting without blowing or shaking out the remaining liquid in the tip.

Summarize the key steps: inspect and rinse the pipet, fill above the graduation mark using a pipet bulb, wipe the outside with lint-free tissue, adjust the meniscus to the mark, and drain into a receiving vessel while retaining the tip on the wall for 5 seconds.