How do you compensate for the ingredients that get stuck to your measuring beaker?

Hi all,

I'm sorry if this is a newbie question but I am just getting started with my formulations.  I have read through a lot of resources on how to formulate properly and know that ingredients percentages are done by weight.  I've also read that this is the best way to scale based on the final amount of product needed.  I am trying to understand how to accurately compensate for the amount of ingredient that doesn't make it into your emulsion because it is stuck to the inside of your beaker.  I don't know the chemist term / equivalent of kerf loss.

For example, when making a lab batch of a o/w emulsion, I use 1% Optiphen as my preservative during cool down phase.  When at scale, this isn't as big of an issue but for a 100ml batch, that 1% is only 1g.  Given such a small amount, I am concerned about the amount of ingredient that gets stuck to the inside of the small beaker that I use to weigh the cool down ingredients.

Maybe I'm over thinking it but I've taken pains to be very precise when weighing my ingredients and this seems to materially change the proportions in the formula.

Thanks in advance,
Nelson

Comments

  • BelassiBelassi Member
    If you use the same beaker for multiple (compatible) things the error is less. Furthermore, you can, after final addition and mixing, pour some back in and then return it to the main amount, thus incorporating pretty much all.
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  • This is one of the reasons measuring by weight is useful. Measuring exactly 100mL of something viscous like glycerin means little if it doesn't get into the end product.

    I would recommend either:
    a) adding whatever you're weighing directly on the scale. If you're making 100mL, just throw the beaker on the scale, TARE, and add 1g into it. This completely eliminates loss between containers.
    b) weigh-by-difference. If you have a small beaker of Optiphen that has a net weight of 50g, pour from it until it weighs 49g. An easier way to do this is put your container on the scale, TARE, and remove so that the scale reads a negative value of the sum of the container weight and the ingredient weight. Pour out what you need, and put it back on the scale, effectively adding back the container weight. The negative value on the scale is how much was removed. This is particularly useful when doing multiple pours from a single container which has residual fluid that may be poured out with what you weighed and lead to over-pours. 

    Also, allowing yourself a +/- range of 1% or so will make life easier.
  • Unknown Member
    Thank you both for the guidance.  I try to minimize the beakers that I use to reduce the transfer loss.  One for the water phase, one for oil phase and one for the cool down phase.

    I had not considered the pour back method @Belassi suggested or the pour out method @alchemist01 shared.

    I will definitely try both to see which works best based on the batch.

    @alchemist01, what is the best way to allow that +/- 1% difference when my percentage is already at 1% like my preservative.?
  • err +/-1% of the value, not 0-2%. So if you're pouring 1g like in your example, you could allot a range of (.99*1)-(1.01*1), or 0.99g - 1.01g. 
    To be clear, the range you allot is for a QC department to tell you or your own standards, not me, 1% was just an example.


  • Unknown Member
    @alchemist01 thanks for clarifying.  I appreciate the response.  I misunderstood the 1% as a full percentage point rather than proportion of my ingredient.
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