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  1. #1

    Default What Determines High & Low Impact for Aroma Chemicals

    Hello Everyone, very new at making perfume (alcohol-based) but I have been reading and paying attention to a lot of these discussions in the forums the past 6 months (great stuff from David Ruskin, pkiler, Chris Bartlett to name a few...). Through a disastrous first round a couple months back, I am realizing dilution is the first adjustment I need to make, especially considering I am making 15 ml bottles of final product at a time.

    At the moment, I have a collection of about 15 aroma chemicals at 100% (4 ml vials) and about a dozen essential oils (1 ml vials) at 100% My plan is to dilute these materials in DPG before blending/testing. I understand some aroma chemicals/essential oils have differing impacts, which will affect the dilution process for each material but my question is: Is there a way to determine a material's impact (high or low) in scientific terms e.g. Pounds per Gallon, Vapor Pressure, etc. or is that just me trying to find the easy way instead of just using my nose?

    Thank you, any advice would help.

  2. #2

    Default Re: What Determines High & Low Impact for Aroma Chemicals

    No, at least for the most part, because it is physiological and depends on the affinity (or perhaps avidity, the difference being binding or dissociation constant vs rate of binding and dissociating) between the odorant and our olfactory receptors. Which in turn depends on our receptors, which aren't easily modeled.

    If not wishing to go just by judgment, a first approach is to use the TGSC odor strength descriptor. For low, there is no particular reason to dilute, although if diluting most materials to 10% then calculations could be easier if diluting low odor strength to 10% as well. For medium odor strength, 10% dilution is typical for accord building and tests if one is in the practice of doing such dilutions which not everybody is. (There's been a recent thread on that.) And for high odor strength, 1% is typical although for really high impact material dilution may need to be even greater.

    The second is to use the percentage used in the odor description (e.g., 100% for linalool, 10% for aldehyde C-10) and divide by 10 if you like to work diluted or do not divide if you don't. And if there's advice in the odor strength listing to not smell above a given percentage, don't go stronger than that in your choice.

    Another way is to choose dilution percentage according to how you or formulas you have studied ordinarily use the product, so as to make measuring practical. For example, if I ordinarily use only about 1 ppt of a material, I will want it diluted at 1%, personally. (I don't mean by this that if say ordinarily I used something at say 5 ppt it would then be 5%: it would be 10%.) And furthermore, to dilute enough so that the material isn't blasting you at the strength you dilute to.

    Anyway, rather than looking at physical properties, those are the approaches I'd recommend for planning it.

  3. #3

    Default Re: What Determines High & Low Impact for Aroma Chemicals

    Quote Originally Posted by scentless_apprenrtice View Post
    What Determines High & Low Impact for Aroma Chemicals
    There's no easy answer to this. There are general trends and loose rules that tend to hold, but it really depends on the specific compound. It has to do with how the shape of the molecule fits and interacts with the receptors in the nose.

    You can separate compounds into different families (alcohols, aldehydes, terpenes, lactones, etc) and divide them based on molecular weight, but that can only help make some rough predictions the level of impact they have. Oftentimes one tautomer will have a lot more impact than another tautomer. It all comes down to exact shape.

    Maybe there is a way to make better predictions, but it would probably get a lot more complicated than you care to get into, and is the field of fragrance chemistry experts.

    One general trend, an alcohol or hydroxy group often makes a fragrance compound more sharp and "potent". Aldehydes also tend to be high impact.
    Higher molecular weight compounds are more likely to be base notes.

    There's also not a precise way to quantify level of olfactory impact. It would be mostly subjective.
    I suppose you could make a scale of 1 to 10 and use a few specific compounds as a "reference point" for comparison.
    In a very loose general sense, you could speak of "high", "medium", and "low", which is not uncommon. But your "medium" might be someone else's "low" for a specific compound.

  4. #4

    Default Re: What Determines High & Low Impact for Aroma Chemicals

    Thank you very much, Bill. This definitely helped my perspective.

  5. #5

    Default Re: What Determines High & Low Impact for Aroma Chemicals

    Quote Originally Posted by parker25mv View Post
    There's no easy answer to this. There are general trends and loose rules that tend to hold, but it really depends on the specific compound. It has to do with how the shape of the molecule fits and interacts with the receptors in the nose.

    You can separate compounds into different families (alcohols, aldehydes, terpenes, lactones, etc) and divide them based on molecular weight, but that can only help make some rough predictions the level of impact they have. Oftentimes one tautomer will have a lot more impact than another tautomer. It all comes down to exact shape.

    Maybe there is a way to make better predictions, but it would probably get a lot more complicated than you care to get into, and is the field of fragrance chemistry experts.

    One general trend, an alcohol or hydroxy group often makes a fragrance compound more sharp and "potent". Aldehydes also tend to be high impact.
    Higher molecular weight compounds are more likely to be base notes.

    There's also not a precise way to quantify level of olfactory impact. It would be mostly subjective.
    I suppose you could make a scale of 1 to 10 and use a few specific compounds as a "reference point" for comparison.
    In a very loose general sense, you could speak of "high", "medium", and "low", which is not uncommon. But your "medium" might be someone else's "low" for a specific compound.
    So basically it's all sort of subjective and relative opposed to one universal "law".

  6. #6

    Default Re: What Determines High & Low Impact for Aroma Chemicals

    It's really a combination of factors. For example if you compare maceal and galaxolide. Both are base notes that last 400 hr. approx. But galaxolide is used neat and maceal is used 1% or even less. If you compare them u notice that for being a base note maceal has a startlingly high vapor pressure. So it's intensity is based on how hard and fast it hits our nose, how fast it dissolves at a molecular level and the fact that green molecules in general are easier to smell than musk molecules.

    Other than reasearch and other people's dilution notes one way to try to come up with a good comparison is to dilute linalool to 50% which is used historically for example. Then compare your new material and dilute your new material to equal strength with your reference material. So linalool 50% and maceal to .01% for example. And of course you have to repeat your observations on at least 3 days.

    However being the art and science of perfumery there are exceptions and weirdness like benzyl salicylate seems to have almost no odor but then mixed it does. Or like geosmin that seems the same strength no matter how you dilute it even down to .001%. or things that are too strong at 10% and impercetable at 1%. Or two things at 10% but together they are 30%.




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