Using a dropping pipette correctly involves several key steps to ensure accurate and contamination-free liquid transfer. It's important to understand not only how to physically use the pipette but also best practices for avoiding contamination.
Steps for Using a Dropping Pipette
Here's a step-by-step guide:
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Prepare Your Solutions: According to the reference, it's essential to avoid contaminating stock solutions. Therefore, always prepare the liquid you need to draw from a separate container, such as a beaker, rather than directly from the stock solution.
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Aspirate the Liquid:
- Squeeze the bulb of the dropping pipette before inserting the tip into the liquid.
- Gently insert the pipette tip into the prepared liquid.
- Slowly release the bulb to draw the liquid into the pipette. Avoid drawing in air bubbles.
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Dispense the Liquid:
- Position the pipette tip over the receiving container or surface.
- Gently squeeze the bulb to dispense the liquid drop by drop.
- Control the pressure on the bulb to achieve the desired drop size and flow rate.
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Prevent Contamination:
- Never insert the pipette tip directly into the stock solution to prevent contamination.
- Always use a clean pipette for each different liquid to avoid cross-contamination.
- Dispose of or properly clean the pipette after use, especially if it has been used with a potentially hazardous material.
Why Avoiding Contamination is Crucial
The provided reference explicitly emphasizes the risk of contamination. When the tip of the pipette comes into contact with a substance, it can carry that substance back into the source solution. The reference uses the example of a pink dye contaminating a stock solution to illustrate this point. This can alter the composition of the stock solution and affect any subsequent experiments or applications using that solution.
Example Scenario
Imagine you need to add a reagent to a test tube. Instead of dipping the pipette into the main bottle of the reagent, you pour a small amount into a clean beaker. You then use the pipette to draw the reagent from the beaker and add it to the test tube. This prevents any possible contamination of the entire reagent supply.
