First ask what “moisture” means
A supplier’s “moisture” line is incomplete without the test method. Loss on drying (LOD) measures mass lost under specified drying conditions, not water alone: WHO’s 1998 medicinal-plant manual explicitly includes both water and volatile matter.[1] For procurement, ask whether the agreed attribute is drying loss or water content before comparing two COAs. This historical manual explains a measurement distinction; it does not establish a current specification for every finished extract.
Loss on drying: retain the conditions
The WHO procedure specifies drying conditions and a weighing endpoint, with provision for the procedure for the material concerned.[1] Request the method identifier and revision, sample preparation and mass, temperature, duration or constant-mass endpoint, and pressure where relevant. Ask the laboratory whether non-water volatile components could contribute to this extract’s loss. Do not relabel a gravimetric LOD result as a water-specific result merely because both are reported as percentages.
Karl Fischer: water-specific does not mean interference-free
Karl Fischer (KF) titration is based on a reaction with water rather than total mass loss; Metrohm also warns that solvent compatibility matters, including aldehydes and ketones, and calls for a solvent blank when samples are dissolved.[3] Ask whether the lab uses volumetric or coulometric KF, direct addition, solvent extraction or an oven, and what demonstrates suitability for the actual extract and carrier matrix. A method name alone does not establish adequate water release or absence of interfering reactions.
An oven is sample preparation, not an automatic solution
In oven-KF, released water is carried to the titration cell; Metrohm describes this approach for insoluble or reactive samples.[2] Oven temperature must release the water without decomposing the sample, and sample-vial blanks and system checks remain important.[2] Ask for the basis for the selected temperature, evidence of complete release, blank correction and recovery checks. Do not copy an instrument article’s example temperature or recovery interval into a purchase specification without a material-specific review.
Compare like with like before accepting a lot
LOD and KF are not interchangeable by default. If a COA reports one while the specification requires the other, request a documented explanation and suitable testing rather than choosing whichever result is lower. Ask: Is the result on an as-received basis? What are the units and calculation basis? Were samples from the same lot, and how were they sealed, stored and handled before measurement? Do not use LOD minus KF as an identified residual-solvent result; any solvent acceptance question needs its own agreed test.
Turn the distinction into a sourcing request
Request the exact SKU and carrier composition, agreed method and revision, lot-specific numerical result, reporting basis and acceptance criterion with its rationale. There is no universal moisture or LOD limit proposed here. Ask who approves a method change and how comparability will be demonstrated before using historical results for trend review. These are buyer review questions, not evidence of testing performed by ZL Botanicals, shelf-life validation or regulatory compliance.