Dry basis correction calculator
Loss on drying from the two balance readings, and a result moved between the as-received and dry bases — with the correction factor itself, which is usually what you apply across a run.
The formula
LOD % = 100 × (wet − dry) / wet factor = 1 / (1 − LOD/100)
- wet
- as-received sample mass
- dry
- mass after drying to constant weight
- LOD
- loss on drying, as a percent of the as-received mass (wet basis)
- factor
- multiply an as-received result by this to put it on the dry basis; divide to go back
Worked example
An assay corrected to the dry basis
A sample weighing 10.000 g as received dries to 9.200 g. The loss is 0.800 g of the original 10.000 g, so LOD = 8.000% and the correction factor is 1 / (1 − 0.08000) = 1.087 — shown here to four significant figures, though the calculator carries it at full precision.
An assay reading 91.2% on the as-received material is therefore 91.2 / 0.9200 = 99.13% on the dry basis. For a positive result at non-zero loss on drying the dry-basis figure is the larger of the two, because the same analyte is being expressed against a smaller mass.
Common pitfalls
Loss on drying is not water content
Drying drives off everything volatile at the stated temperature — water, residual solvent, and anything else that leaves. Karl Fischer titration measures water specifically. Where a monograph names one, the other is not a substitute, and swapping them produces a wrong number that looks entirely reasonable.
Moisture is a fraction of the as-received mass
Loss on drying is expressed against the original wet mass, which is the convention in pharmaceutical, food and environmental testing. Some industries express moisture against the dried mass instead; for the same sample that gives a different figure. This calculator is wet basis throughout.
Correcting a result that is already on the dry basis
Applying the factor twice is invisible in the arithmetic and wrong by the square of the factor. Before correcting, check what basis the method reports on — an assay already stated as anhydrous or dried needs nothing further.
The drying programme is part of the result
Temperature, time, sample thickness and whether the oven was under vacuum all change how much mass is lost. An LOD figure without its conditions is not reproducible, so record them alongside the number.
Correcting a rounded result
Apply the factor to the full-precision result, not to the value you rounded for the report. Rounding first carries the error into everything downstream — the same reason the calculators here round only at display.