Beginner perfumer · 77
How wide is the assay window — 86 of 1,794 materials have ends more than ten points apart
· 11 min read
The assay field rarely gives one number. It gives a range like "95.00 to 100.00", and that range is how much two bottles under the same name can differ. I measured the width across 1,794 materials with ten or more suppliers whose assay is written as a plain low-to-high: five points is commonest at 30.9%, then two points at 24.4% and one point at 17.1%. Eighty-six records (4.8%) are ten points or wider, and they include materials you actually use — beta-caryophyllene at 61 suppliers reads 80 to 100, rhodinol at 41 reads 70 to 100, camphene at 39 reads 80 to 100, pine oil at 38 reads 80 to 100. Three distinct causes are visible in the data, and they mean different things for you.
About 4 minutes.
The assay field rarely gives you a number. It gives you this:
95.00 to 100.00
That is not an error bar; it is a specification. It says any material meeting this range counts, and it does not tell you where your bottle falls.
So the question worth asking is: how wide is the range?
Measure it
Pulling materials with ten or more suppliers whose assay field is written as a plain low-to-high gives 1,794 records.
| Range width | Records | Share |
|---|---|---|
| 5 points | 555 | 30.9% |
| 2 points | 437 | 24.4% |
| 1 point | 306 | 17.1% |
| 3 points | 235 | 13.1% |
| 4 points | 105 | 5.9% |
| 10 points | 28 | 1.6% |
| 8 points | 25 | 1.4% |
| 15 points | 12 | 0.7% |
Over 90% sit within five points. That is the norm for this field and the default you can assume.
And 86 records — 4.8% — are ten points or wider.
Those 86 include materials you use
Sorted by supplier count, the top entries are not obscure:
| Material | Suppliers | Assay range | Width |
|---|---|---|---|
| Melon heptenal | 65 | 85 to 100 | 15 |
| Beta-caryophyllene | 61 | 80 to 100 | 20 |
| Myrcene | 56 | 90 to 100 | 10 |
| (E)-beta-damascone | 41 | 90 to 100 | 10 |
| Rhodinol | 41 | 70 to 100 | 30 |
| Camphene | 39 | 80 to 100 | 20 |
| Pine oil | 38 | 80 to 100 | 20 |
Rhodinol reads 70 to 100 — thirty percentage points. Both bottles are in spec, and one of them can be 30% something else.
(The list also holds very wide ranges on things that are not fragrance materials: hydrochloric acid at 10 to 100, lecithin at 60 to 100. Those are reagents and raw materials, outside this article.)
Three causes of a wide range
Reading the other fields on these records shows at least three different reasons, and they mean different things.
One: the name refers to a mixture in the first place
Rhodinol's head_synonym field reads:
3,7-dimethyl-6 & 7-octen-1-ol
"6 & 7" — two positional isomers sharing one trade name.
So part of that 70-to-100 range is not impurity; it is what the name covers. The ratio you receive will vary, and the supplier has not broken spec.
(One name covering more than one thing is more common still among naturals, measured in A third of the records sharing a CAS.)
Two: the synthesis does not run clean
Camphene's formulations field says:
commercial product may contain approx 20% tricyclene. … grades of purity: commercial, 75% or greater.
That is not a quality-control failure; it is chemistry. Camphene is made industrially by isomerising α-pinene, and that reaction yields camphene and tricyclene together — two products of the same carbocation rearrangement. (The full story is in its own material guide.)
What this class means for you: that 20% is predictable, and you can look up what it is.
Three: it is a deliberately made-up solution
Phenyl acetaldehyde solution on the list reads 45 to 55 — not unstable purity, but how a spec for "about a 50% solution" gets written.
This class announces itself. Converting a dilution back to neat before calculating a formula is something I did in Five people diagnosed the same formula.
What to do
- Read the width, not just the floor. 95-to-100 and 80-to-100 are different things even though they share an upper bound.
- Within five points is normal; ten or more is worth asking about. Request the batch's actual certificate of analysis rather than accepting the spec range as the answer.
- When the range is wide, read
head_synonymandformulations. Those two fields often say outright what the remaining fraction is. - Re-evaluate wide-range materials when you change supplier. Two bottles both in spec is not two bottles alike.
- If a material in your formula is hard to reproduce, check its assay range first. It may not be your technique.
What this doesn't establish
- This is a field audit, not a quality survey. I measured how specifications are written, not the purity distribution of material actually on the market.
- The 1,794 are the subset whose assay is a plain "lo to hi". Entries like "85.00 to 100.00 sum of isomers", or single numbers, are excluded.
- Ten or more suppliers is my threshold, and changing it changes the numbers.
- The "three causes" are my classification, read off other fields. No field explains why a range is the width it is, and most records leave both of those fields empty, so I can only make this judgement for the few that fill them in.
- An upper bound of 100 does not mean 100 is available. It is the top of a specification.
- I requested no certificate of analysis from any supplier. This article is entirely database fields.