Hi Rajpal,

First, you have to make sure that the cream is o/w and not w/o. Only for the o/w sytem based products, you should do the pH of the finished product (as is) using a properly calibrated pH meter and then (5o% dilution with water.) This will give you the true pH of your product.

Good Luck!

Dr. Babar

Dr. Almas Barbar-

how to measure PH for the w/o cream (cold cream) is it possible? Do we not go for PH for w/o emulsion??

for o/w cream if we dilute 50 % with water then will it not affect the PH of formulation?

other question, in my lab basic formulation to deal with w/o emulsions and cold cream.

for estimating size range of w/o nanoemulsion, i will dilute it with external phase of oil, then for malvern instrument ZS90, what to put in refractive index value and viscosity, of water or oil ???

Plz reply............Dr. Almas Barbar

Thanx

You only can measure ph accurately in a system with water as the outer phase. If it is the inner phase you maybe can measure ph of it before you emulsify the aqueous phase in your lipid phase. Think about the definition of ph value - there's no "pH" in the oil.

For dynamic light scattering you measure the brownian movement of your inner phase (your droplets in the nanoscale) in the outer phase. So you have to apply the viscosity and optical parameters of the outer phase.

There is a pH meter especially designed for emulsion cream, you may need to look for the one with "cream probe"

For w/o emulsion creams take 10g of the sample to be tested and add 90ml of rectified spirit whose pH has been adjusted to 6.5-7.0. Warm it to 45 0 C and stir for 15 minutes. filter off the alcoholic layer using a filter paper and then measure the pH the pH meter at 270C

The pH can be measured by making 50% solution of o/w cream.

Is there any ISO/pharmcopeia regarding the pH measurement of creams, particularly Water-in-Oil emulsions? There seem to be several answers and methods, from simple dilution in DI water to "reformulating" with heated alcohol.

As I am aware, there is no standard method for pH measurement in w/o emulsions. even if you try to dilute it in DI water because the w/o emulsion is not going to disperse in water!! you can say it is insoluble in water. Heating in alcohole can affect the pH as well. As a result the only way is considering the water phase pH as the final product's pH of course if you are not going to add acid or base into your product after emulsion formation.

Shiva Sabzevari Thanks.

If my oil phase has some organic acid or base in it, which may somehow partition into the water phase during emulsification, would that create a difference in the pH before and after mixing?

If it is an oil, it means that it does not intract with water so it is not going to change the pH of emulsion.

Shiva Sabzevari Theoretically, while mixing/emulsifying, some of the oil ingredients may partition a little into the water. In general, I think it would be best to limit pH measurements to the aquoeus phase, and not go near oil/mixed emulsions, however there seem to be several schools of thought.