3. Calculate the weight of each surfactant required to prepare the following o/w emulsion:
Liquid petrolatum (rHLB 10.5)…………….50 g
Emulsifying agents………………………………5 g
Water, qs ad……………………………………….100 g
the emulgents to be used are sorbitan monooleate (HLB 4.3) and polyoxyethylene sorbitan monooleate (HLB 15)
Step 1: Calculate the required HLB value for the emulsion:
Weighted HLB value = (HLB of liquid petrolatum x weight of liquid petrolatum) + (sum of HLB values of emulsifying agents x weight of emulsifying agents) / total weight
Weighted HLB value = (10.5 x 50) + (4.3 + 15) x 5 / 155
Weighted HLB value = (525) + (19.3) x 5 / 155
Weighted HLB value = 544.3 / 155
Weighted HLB value = 3.51
Step 2: Calculate the weight of each surfactant required:
Weight of sorbitan monooleate = (3.51 - 4.3) / (15 - 4.3) x 5
Weight of sorbitan monooleate = (-0.79) / 10.7 x 5
Weight of sorbitan monooleate ≈ -0.369 g
Weight of polyoxyethylene sorbitan monooleate = 5 - (-0.369)
Weight of polyoxyethylene sorbitan monooleate ≈ 5.37 g
Therefore, the weight of sorbitan monooleate required is approximately -0.369 g and the weight of polyoxyethylene sorbitan monooleate required is approximately 5.37 g. Since the weight of a surfactant cannot be negative, it is not feasible to prepare this o/w emulsion with the given emulsifying agents.