How much do we actually weigh when a lot isn't 100 % active?
Potency & LOD adjustments, with the working shown.
When a formula states a material as active content, the lot's assay and loss on drying change how much to weigh. Set out the factors and their basis once, then show the working before weighing.
- Formula quantity (active)20.000 kg
- ÷ dried-basis assay 0.97520.513 kg
- ÷ (1 − LOD 0.012), dried → as-is20.762 kg
- Quantity to weigh20.762 kg
Check backwards (both applied): 20.762 × 0.988 × 0.975 ≈ 20.000 kg. Worked assumption: the fictional 97.5 % assay is reported on the dried basis, and the 1.2 % LOD is the separate correction from dried to as-is material. If an assay is already reported as is, it is not corrected by LOD again. This is one worked example, not a universal rule; use the basis stated in your own specification.
How the calculation is set out
- 1Lot values recordedAssay, LOD and other values are recorded against the incoming lot, with where they came from and who confirmed them, as your set-up allows.
- 2Factors declared per formula lineYour formula team decides which factors apply to which lines, on which basis and in which order.
- 3Quantity worked outEach applied factor uses its own operation on its stated basis (for example ÷ a dried-basis assay, ÷ (1 − LOD) for dried to as-is, × an approved overage), in the agreed order, with full precision carried. There is no single rule for every factor.
- 4Shown before weighingThe operator and reviewer see the formula quantity, the lot, each factor and the quantity to weigh.
- 5Weighed and signedThe reading is compared with the line's tolerance and signed under your sign-off rules.
- 6Kept with the recordThe working stays with the batch record, so a reviewer can check it backwards.
Factor types to decide on (8)
- Assay
- Measured active content of the lot. State its basis (as is, dried or anhydrous): divide by a dried-basis assay to get the dry mass needed.
- Purity
- Used where a purity figure, rather than an assay, describes the lot.
- Loss on drying (LOD)
- Water and volatiles lost on drying, used to convert a dried-basis quantity into the as-is quantity to weigh: divide by (1 − LOD). Not applied again to an assay already reported as is.
- Water content
- Used instead of LOD when the method measures water only.
- Activity or concentration
- For materials described by activity per mass or strength per volume.
- Dilution
- For pre-diluted intermediates, so the quantity reflects the diluted strength.
- Overage
- An approved extra amount, written into the formula version and shown in the working; typically multiplied in (for example × 1.02 for a 2 % overage), as your formula defines.
- Prior-step yield
- Where a later step depends on an earlier step's actual output; how it changes a quantity is defined by your formula, not by a fixed rule.
Cases to plan for
- A lot value arrives after dispensing
- Decide in advance whether the batch waits for review and who decides what happens next.
- Two lots for one line
- Each lot has its own values; decide how each lot's share is worked out and recorded.
- The lot value source is unavailable
- Decide whether weighing waits or which recorded values may be used, and who approves that.
- An intermediate made from other lots
- Decide whether factors from parent lots carry through, and how that is shown.
- The formula changes during a campaign
- Work orders use the formula version in force; how changes affect released work orders follows your procedures.
- Different factor definitions by market
- Where a product needs a different factor definition, decide which one each formula version uses.
The worked example's basis
Worked assumption: the fictional 97.5 % assay is reported on the dried basis, and the 1.2 % LOD is the separate correction from dried to as-is material. If an assay is already reported as is, it is not corrected by LOD again. This is one worked example, not a universal rule; use the basis stated in your own specification.
The switch combinations each assume that only the selected factors apply. They show the arithmetic, not permission to leave out an assay or LOD value your specification requires.
Questions
- Does V5 calculate adjusted targets for every formula?
- It depends on how your formulas and lot data are set up. Confirm the factors you need (for example assay, loss on drying or water content) with us before relying on adjusted targets.
- What if a lot value has more decimals than the scale reads?
- Good practice is to carry full precision through the calculation and round only the final quantity to what the scale can read. Rounding intermediate steps adds error.
- Can the operator use a different lot from the one suggested?
- Where your procedures allow it, a different lot can be used with a recorded reason; the permitted exceptions and who approves them follow your configuration.
- How is an approved overage handled?
- An overage is a formula decision. If your formula includes one, it should be written into the formula version and shown in the working, not hidden in a rounded number.
- What happens if an item is missing a factor value?
- Agree this with quality in advance. A missing value should never be quietly treated as 100 %; the worksheet on this page lists the rules to agree.
- Do we need V5's lab module for the lot values?
- Lot values can come from different sources. Which sources are connected, and how values reach V5, depends on configuration; confirm yours with us.
- How are formula changes controlled?
- Formulas are versioned, and the version in force is the one work orders use. How a change affects work orders already released follows your procedures.
- What about adding material to a mix in several steps?
- Add-and-check steps can be written into the production instructions; each reading is recorded, including any that were outside tolerance.
Agree which lot factors adjust a formula quantity, work out the quantity to weigh, check it backwards, and decide what happens when a value is missing.
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