sunscreen spray - Chemists Corner

Formulating

sunscreen spray

Posted by crisbaysauli on January 12, 2015 at 9:25 pm

Happy new year everyone!

Here I am again, having some problems with our formulations.

Now, we are doing a clear sunscreen spray witht the following composition

Alcohol

Isopropyl myristate

Octocrylene

Avobenzone

OMC

Benzo 3

BHT

Problem is, pH decreases from 4.8 to 3.20 during our stability study. Can someone help me explain this?

Bobzchemist replied 9 years, 9 months ago 6 Members · 12 Replies
12 Replies

Chemist77

Member
January 13, 2015 at 12:28 am

The breakdown of your sunscreen agents is the only cause that seems to be into play here. Check the temperature dependent degradation rates of your sunscreens and it would give you a fair idea about this phenomenon.
Bill_Toge

Member
January 13, 2015 at 3:04 am

in my experience, pH meters are notoriously unreliable in solvents other than water; the lower conductivity of the medium, hence the lower current, results in loss of precision and greater variation in readings

the most common way to resolve this is to add a fixed reference electrode to your pH meter
chemist1

Member
January 14, 2015 at 10:48 am

A version that I worked on was the following:
Finsolv TN G - 10%
OMC - 7.5%
Octyl Salicylate - 4.0%
Isododecane - 73.5%
Isohexadecane - 5%
Fragrance - QS

This had a really nice feel and was stable.
Iaskedbetter

Member
January 14, 2015 at 12:36 pm

Your formula does not have a pH, as it is anhydrous. You will get a reading when you use a pH meter, but that is not the pH.

Ethanol has a pHe value, which is not the same as pH and requires a specialized electrode. Regardless, I would say you are better off forgetting about pH in an anhydrous product altogether.
crisbaysauli

Member
January 26, 2015 at 12:08 am

@Iaskedbetter do you have a reference printed material on this one? It might help me explain to our marketing group.

@chemist1 did you have any issues about the pH?

@Bill_Toge can you recommend a supplier for this fixed reference electrode?
Bill_Toge

Member
January 26, 2015 at 8:29 am

sorry, I misread the thread originally and somehow thought there was water in this formula

I agree with @Iaskedbetter, the pH reading in an anhydrous product is totally irrelevant; reference electrodes are only meaningful or useful when measuring the pH of water/solvent mixtures
Iaskedbetter

Member
January 26, 2015 at 7:32 pm

http://fscimage.fishersci.com/cmsassets/downloads/segment/Scientific/pdf/foodtrack_summer_07.pdf

“The ASTM D6423 method is a procedure to measure the relative acid strength of high ethanol content fuels containing about 70% or more ethanol. Acid strength is determined by measuring the pHe of fuel, which is similar but not directly comparable to the pH of a water solution.”

pHe is important in the fuel industry because a high corrosion potential can wreak havoc on the internal parts of an engine. For cosmetics, we really only need to conduct package compatibility testing.
Bobzchemist

Member
January 27, 2015 at 5:41 pm

http://fscimage.fishersci.com/cmsassets/downloads/segment/Scientific/pdf/foodtrack_summer_07.pdf

http://www.astm.org/Standards/D6423.htm

When we tried to pH test our sunscreen spray here, it was always diluted in water, but it didn’t help enough. There can be no pH reading without water, so you really should just tell management that the readings you got were meaningless.
Bobzchemist

Member
January 27, 2015 at 5:42 pm

http://www.fishersci.com/ecomm/servlet/cmstatic?href=Scientific/researchAnalytical/ProductsServices/Food_Diagnostics/food_beverage_newsletter_ph_electrode.jsp&store=Scientific&segment=researchAnalytical&storeId=10652
crisbaysauli

Member
January 29, 2015 at 8:22 am

Thanks so much guys. I just had a meeting with our marketing and QA group and they were also awed by the realization that oils do not have pH! Thank you.
Bobzchemist

Member
January 29, 2015 at 3:06 pm

This is the one we make here at Beaumont - just in case anyone at your place is tempted to think that I’m giving advice that isn’t based on relevant experience:

http://dermatone.beaumontproducts.com/sunscreens/dermatone-continuous-spray-sunscreen
Bobzchemist

Member
January 29, 2015 at 3:08 pm

Also, we will private label any of our sunscreen products - just in case anyone’s interested.