Two certificates can both be correct and still disagree. When nicotine on one is 2.4% and on the other 2.7%, the cause may be nothing more than the basis: as-received counts the water in the sample, dry basis does not.
Two bases, one lot
As-received (also called as-is or wet basis) expresses a constituent as a percentage of the material exactly as it arrived at the laboratory, water included.
Dry basis (dry weight basis) expresses it as a percentage of the material with water removed by calculation.
Tobacco is hygroscopic and exchanges water with the air, so the moisture in a lot changes with storage and transit. If a result is reported as-received, it carries that variation with it. A dry-basis result is more stable because water has been taken out of the denominator.
The conversion
Let M be the moisture content as a fraction (12% moisture is 0.12).
- As-received to dry basis: Dry % = As-received % / (1 − M)
- Dry basis to as-received: As-received % = Dry % × (1 − M)
The moisture value should come from a named method on the same sample, or a split of it, taken at the same time. CORESTA Recommended Method No. 76 defines moisture content (oven volatiles) by drying in a forced-draft oven at 100 °C ± 1 °C for three hours. ISO 6488 (current edition 2021) specifies a Karl Fischer method for water content. The two are different measurements, so the conversion should state which was used.
Worked example (illustrative numbers only)
The figures below are invented to show the arithmetic. They are not Indileaf data and not a typical or promised specification.
Assume a lot whose true nicotine content is 2.73% on a dry basis. The same material tested at different moistures reads as follows.
| Moisture at test | As-received nicotine (illustrative) | Dry-basis nicotine |
|---|---|---|
| 8% | 2.51% | 2.73% |
| 12% | 2.40% | 2.73% |
| 16% | 2.29% | 2.73% |
Calculation for the 12% row: 2.73 × (1 − 0.12) = 2.40. Reversing it: 2.40 / 0.88 = 2.73.
The as-received figure moves by more than 0.2 percentage points across this range, although the leaf has not changed. If a contract set a minimum of 2.5% as-received, the same lot would pass at 8% moisture and fail at 12%. That is the practical risk of leaving the basis unwritten.
How moisture swings move results
Three situations commonly produce a gap between two reports:
- Different test dates. A sample that sat in an open container gained or lost water before analysis.
- Different moisture methods. Oven volatiles and Karl Fischer can differ slightly, which flows into the conversion.
- Different sub-samples. Moisture is measured on one portion and nicotine on another that has since changed. Good practice is to determine moisture on the same prepared sample at the time the nicotine portion is weighed.
CORESTA Guide No. 13 recommends that sample containers be airtight and preferably opaque, and that samples be stored dry and cool, away from light. If the sample was not protected, even a correct conversion cannot recover the original condition.
Methods are a separate question
The basis answers only one part of the comparison. Methods for nicotine also differ. CORESTA publishes recommended methods for total alkaloids (CRM 85) and for nicotine by gas chromatography (CRM 62). Titration is widely used for quick checks but is not a CORESTA method. A complete line therefore reads: nicotine, minimum value, method, basis.
Why this matters for scrap and by-products
Nicotine-extraction buyers pay for nicotine yield, so a basis mismatch becomes a commercial difference. For high-nicotine scrap, a few tenths of a percentage point of nicotine is material, so agree the basis and method before the first shipment. Scrap and dust also equilibrate quickly with ambient air, which makes moisture handling at sampling especially important.
Reading a certificate in four steps
- Find the moisture figure and the method that produced it.
- Find the basis printed next to each result. If none is printed, ask before accepting the number.
- Convert the result to the basis in your contract using the formula above, and keep the working.
- Compare on that single basis, then compare methods, then compare samples. Taken in this order, the steps often resolve an apparent disagreement before anyone suspects the laboratory.
Contract wording tips
- State the basis for each constituent: "Nicotine, minimum (x)% on a dry-weight basis."
- Name the moisture method: "Moisture by CORESTA Recommended Method No. 76" or "water by ISO 6488."
- Say whether commercial weight is as-received or adjusted.
- Require that results on certificates show both the as-received value and the moisture, so any reader can convert.
- Name a referee laboratory and the method it will use in a dispute.
- Define the sample: who draws it, how it is sealed, and how soon it must reach the laboratory.
Frequently asked questions
Which basis should a contract use?
Either can be used if it is written down. Many buyers specify the nicotine minimum on a dry basis and state the moisture method, because that makes lots of different moisture comparable.
Does the moisture method change the dry-basis result?
It can. Oven volatiles and Karl Fischer water content are different measurements, so the moisture figure used in the conversion should come from a named method.
