pH

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nurul
nurul's picture
pH

Dear all,

I would like to ask which one is the correct way to determine pH for cosmetic products like shampoo, day cream, night cream and etc.

First:
To immerse the pH probe directly into the sample

Second:
To prepare 10% of sample dilute with DI water and then immerse the probe

Which one is the correct way.

Thanks

PhilM
PhilM's picture
 without diluting the sample

 without diluting the sample you could use litmus paper to determine if the product is acidic (pH 1-7) or basic (pH 7-14)

Then you can select an appropriate range piece of pH paper to determined its pH more exactly.

nurul
nurul's picture
Thanks for the reply,

Thanks for the reply,

But I dont have litmus paper, I only have pH meter. Thats why I want to know do i need to dilute the sample? If anyone know the standard method, can u pls tell me.

Thanks

Raashmi
Raashmi's picture
Hi Nurul,

Hi Nurul,

Diluting your samples will cause change in the pH. A litmus paper is a very crude way of determining pH which will not give you exact pH thats why for you its best to use Litmus paper rather than pH meter. As all the creams are very viscous and diluting it will change their pH.

Here's something i got:

When acids are diluted, the pH goes up toward 7. When alkalis are diluted, the pH goes down toward 7. A tenfold dilution of hydrochloric acid will change its pH by 1 pH unit, as will a tenfold dilution of sodium hydroxide. This is because the dilution of hydrochloric acid changes the concentration of hydrogen ions (H??+) by a factor of ten. It is the concentration of H??+ ions that determines the pH.

 

fringe
fringe's picture
hi Nurul,

hi Nurul,
don‘t diluting your samples,and diluted sample don’t show realy sample PH.
IF the sample is diluted ,the PH will get chose to 7.
So immerse the PH directly.
If you don't want to immerse the PH derectly and you also don't want use litmus paper.