Accurately
weigh
approximately
0,05 g 4-hydroxybenzoic acid (2.3),0.2 g salicylic acid(2.4),0.2 g benzoic acid (2.5) and 0,05 g sorbic acid (2.6)in a 50-ml volumetiric flask and make up to volume with ethanol/water mixture (2.13).Store this solution in a refrigerator.The solution is stable for one week