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

Annex. Reagents and their preparation 361Methylene blue solution (No. 39)Methylene blue 0.3gDistilled water100mlDissolve the methylene blue in the distilled water. Filter the solution into a cleanbrown bottle. Label the bottle “METHYLENE BLUE SOLUTION” and writethe date.Neutral red, 1g/l (0.1%) solution (No. 40)Neutral red1 gDistilled waterq.s. 1000mlDissolve the neutral red in about 300ml of distilled water in a clean 1000-mlbottle. Make up the volume to 1000ml with distilled water and mix well. Labelthe bottle “NEUTRAL RED 0.1% SOLUTION” and write the date. Store at roomtemperature.Pandy reagent (No. 41)Phenol (C 6H 5OH)30gDistilled water500mlPut the phenol in a 1000-ml bottle. Add the distilled water and shake vigorously.Label the bottle “PANDY REAGENT” and write the date. Leave to stand for 1day. Check whether any phenol remains undissolved. If so, filter. (If all the phenolhas dissolved, add a further 10g and wait another day before filtering.) (Pandyreagent is a saturated solution of phenol.)Warning: Phenol is highly corrosive and poisonous.Phenol red, 10 g/l (1%) solution (No. 42)Phenol red crystals 0.1gDistilled water10mlWeigh out the phenol red crystals in a 20-ml beaker. Add the distilled water and stiruntil the crystals have dissolved. Transfer the solution to a plastic dropper bottle.Label the bottle “PHENOL RED 1% SOLUTION” and write the date. Store atroom temperature (20–25°C).Phosphate-buffered water, 0.01mol/l, pH 6.8 (No. 43)1. Prepare a stock solution of anhydrous sodium dihydrogen phosphate in a 1000-ml volumetric flask:Sodium dihydrogen phosphate, anhydrous (NaH 2PO 4) 13.6gDistilled waterq.s. 1000mlSterilize the stock solution by filtering it through a 0.2-mm pore size filter. Ifanhydrous sodium dihydrogen phosphate is not available, the solution can beprepared by dissolving 17.2g of sodium dihydrogen phosphate dihydrate(NaH 2PO 4·2H 2O) in 1000ml of distilled water. Label the volumetric flask “AN-HYDROUS SODIUM DIHYDROGEN PHOSPHATE” and write the date.Keep the stock solution in a refrigerator.2. Prepare a stock solution of disodium hydrogen phosphate in a 1000-ml volumetricflask:Disodium hydrogen phosphate, dihydrate(Na 2HPO 4·2H 2O) 17.8gDistilled waterq.s. 1000ml