![]() ![]() Micropipettes (or micropipets) have been calibrated with high precision and accuracy in order to quickly and easily transfer specific volumes of solution. Check the markings carefully to determine the type of graduated pipet you are using. Some graduated pipets can be filled to the desired level and then drained completely. Its use requires an initial meniscus reading and a final meniscus reading the volume delivered is the difference between the two readings as is the case with a buret or a graduated cylinder. Most of the techniques for using the graduated pipet are similar to those for the transfer pipet with the exception that for most graduated pipets one does not deliver a measured volume by allowing the graduated pipet to completely drain. Note: Whereas the transfer pipet can be used only to deliver a fixed volume of liquid, the graduated pipet will deliver varying amounts. Do not blow or shake out the small amount of liquid remaining in the tip this has been included in the calibration. Keep the pipet tip in contact with the container wall for about 15 seconds after emptying. ![]() To deliver the desired volume hold the pipet in a vertical position, and drain the solution into the container with the tip of the pipet touching an inner wall of the container. To reduce parallax put the meniscus at the same level as your eye so that the front and back sides of the etched line coincide. Quickly remove the bulb, cover the stem end with your index finger as described above, and then carefully allow the bottom of the meniscus to drop to the calibration mark. Using the rubber pipet bulb in the manner described above, fill the pipet to several centimeters above the calibration mark. Without further rinsing of the beaker, add fresh solution to the beaker. ![]() Dry the outside of the tip with tissue, and discard the excess rinse solution in the beaker. Roll the pipet back and forth in a horizontal position to wet thoroughly the entire inside surface by partially releasing the index finger seal as necessary. Another method of conditioning the index finger is to wet it with water and dry it with a paper towel. For a well- conditioned index finger, try rubbing it in your palm. If your finger is too dry it will be difficult to maintain a satisfactory seal, but if it is too moist you will have trouble with precision control of the flow rate. Quickly remove the bulb and cover the upper end of the pipet with the index finger of your dominant hand to control the liquid flow. Prevent liquid from entering the bulb, which will easily happen if the pipet tip is removed from the solution while there is still suction in the bulb. Before using the bulb make sure there is no liquid inside of it.ĭraw a few mL of solution into the pipet by gently holding together the pipet bulb and the upper end of the pipet (do not force the pipet bulb onto the end of the pipet), squeezing the air out of the bulb, immersing the pipet tip into the liquid in the beaker, and carefully releasing the bulb just enough to draw the desired quantity into the pipet. Do this by placing about 15 mL of the solution in a clean, dry 50 mL beaker. Prior to pipetting a solution, rinse the pipet with several small portions of the solution. Handle pipets with great care to avoid bumping the tip against a hard surface. A broken tip may slightly alter the volume delivered. Before using the transfer pipet check the delivery tip for possible breakage. There will be a small residual volume of liquid remaining in the tip after the draining has ceased. When filled to this mark the pipet will deliver its rated volume if it is allowed to drain freely. ![]() The transfer pipet has a single calibration mark etched on its stem.
0 Comments
Leave a Reply. |