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mg per spray pump
I have make sure our otc ingredient is approximately 10 mg’s per metered spray. Not sure how to do the calculation. I am sure I have to get the weight of the liquid being “sprayed” for the spray component. Any suggestions?
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2 Replies
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Approximately is your friend.I don’t know the Monographs well enough to even give a general bit of advice like -/+ 10%, but I do know that companies are given some freedom to set there range of specification on Active Ingredients.Stoichiometry is what you need to do, and it’s my favorite.1.) Define your diluent. What is going to be the bulk of you formula, water, oil, alcohol, isododecane, etc. (hell if you have a formula base already in mind use that)2.) Determine the diluent of formula base without actives density. A single ingredient may have a literature value, but always test yourself, and keep your temperatures consistent.3.) Tare an empty vessel on a scale, then collect 10 or more metered sprays of the diluent or active free formula into that vessel.4.) With the average weight per spray and the known density, you’ll easily find the volume per spray.5.) By using the diluent or active free formula base you could assume little change in the volume per spray with the addition of the active.6.) Keep in mind that if you active is a soluble solid it will likely increase the density of your solution.7.) Perform a specific gravity check on a solution you believe through calculation will deliver the 10 mg of active per average spray volume.8.) With your new test formula again collect 10 or more sprays and find the average weight per spray, and determine if the average volume per spray has changed. Hopefully not much. Then you have an approximate dosage per spray so long as your packaging is consistent and qualified.9.) Repeat this on enough duplicate sprayers that would justify the “metered sprayers” are reliable and consistent in their volume per spray.10.) Put that formula on accelerated stability, and if it fails start over easy peasy.Good Luck -
To get the average dispensed volume you trigger the pump several times
i.e. 20, 50, 100 times
pour liquid in a accurate graduated cylinder, measure it and divide by the number of sprays.
https://en.wikipedia.org/wiki/Graduated_cylinder
Now to determine the variation
you’ll need accurate equipment
IMO the best way to do it, without spending too much is to get a microliter syringe.
https://www.hamiltoncompany.com/products/syringes-and-needles/general-syringes/microliter-syringes
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