Manual of basic techniques for a health laboratory - libdoc.who.int

3. General laboratory procedures 79Soaking in waterAfter rinsing, place the pipettes in a large, plastic measuring cylinder (or bowl) fullof water. If the pipettes have been used to measure infected material, leave them ina cylinder full of disinfectant solution (e.g. a quaternary ammonium compound or1% bleach solution; see pages 84 and 85) for 4 hours.Soaking in detergent and rinsingFollow the instructions given above for soaking and rinsing of laboratoryglassware.Blocked pipettes1. Put blocked pipettes in a cylinder filled with dichromate cleaning solution (reagentno. 20). Slide them carefully into the solution and leave for 24 hours.2. The next day, pour the dichromate solution into another cylinder (it can be usedfour times).3. Hold the cylinder containing the pipettes under the tap and rinse thoroughly.4. Remove the pipettes one at a time. Check that the obstruction has been washedaway. Rinse again.5. Leave to soak in ordinary water for 30 minutes, then change the water and soakfor a further 30 minutes.Warning: Dichromate cleaning solution is highly corrosive and should be used withextreme care. If it is accidentally splashed on the skin or clothing or into the eye(s),wash at once with large quantities of water.DryingDry heat-resistant glass pipettes in a hot-air oven at 60°C and ordinary pipettes inan incubator at 37°C. Alternatively, leave pipettes to air-dry.Using the vacuum pumpThis is a small instrument made of metal, plastic or glass that is attached to thewater tap.1. Turn the water on hard to drive a strong jet through the pump. This causes airto be sucked into the side arm of the pump and the rubber tubing attached toit.2. Fit this rubber tubing over the tip of the pipette.3. Dip the other end of the pipette into the rinsing liquid (water or detergentsolution), which is sucked through the pipette and discharged by the pumpinto the sink (Fig. 3.59).Microscope slidesNew slidesSoaking in detergent solutionPrepare a bowl of water mixed with washing powder or liquid detergent. Use theamounts recommended by the manufacturer. Place the slides in the bowl one byone and leave to soak overnight.Rinsing in waterRinse each slide with tap water and then soak in clean water for 15 minutes.Fig. 3.59 Using a vacuum pumpto rinse a pipette