Pharmacopoeial Titration Assay Calculator
Per cent assay from titre, blank, factor and the monograph’s equivalent, with the RSD.
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About the Pharmacopoeial Titration Assay Calculator
Works out a titrimetric assay the way pharmacopoeial monographs write it: the titre less the blank (or, in a back titration, the blank less the sample's titre), times the factor of the titrant, times the monograph's "each mL of … is equivalent to … mg", divided by the quantity weighed. It handles direct, back (residual) and non-aqueous titrations, corrects the volume of a non-aqueous titrant for the difference between the temperature of standardization and of the assay, and can report on the dried or anhydrous basis or as a per cent of the label claim.
With up to six replicates it gives each result, the mean, the standard deviation and the RSD, rounds the result the way The International Pharmacopoeia's General Notices say (to one decimal more than the limits, then to the limits' decimals) and compares it with the monograph's limits. It also checks each weight against the stated quantity and a non-aqueous blank against the usual ceiling. Without a pass it shows a free preview: the method, the limits that apply and the verdict, with every computed figure hidden; the figures, the working and the PDF, Excel and Print exports unlock with a Premium pass.
How to use it
- Choose the titration: direct, back (residual) or non-aqueous.
- Enter the titrant’s nominal molarity and its factor (or its actual molarity), and the monograph’s mg equivalent to 1 mL — or let the tool work it out from the molar mass and the moles of titrant per mole of substance.
- Enter the blank and, for each replicate, the quantity weighed and the titre. For a back titration the titre is that of the back titrant.
- For a non-aqueous titrant, enter the temperatures at standardization and at the assay; add the limits from the monograph, typed with their decimals.
- Read each replicate, the mean, the RSD and the verdict. Without a pass the report stays a free preview with its figures hidden; the PDF, Excel and Print unlock with a Premium pass.
Examples
Sodium acetate R: 0.4012 g · 0.1 mol/L perchloric acid, factor 1.0023, standardized at 22 °C, used at 25 °C · titre 29.42 mL, blank 0.08 mL · each mL ≡ 13.61 mg (illustrative readings)
(29.42 − 0.08) × [1 + 0.001 × (22 − 25)] = 29.252 mL · × 1.0023 × 13.61 = 399.04 mg · ÷ 401.2 mg × 100 = 99.46 %
The International Pharmacopoeia’s reagent entry for sodium acetate R gives the equivalent of 13.61 mg and requires not less than 99.0 %.
1.5023 g in 0.5 mol/L reagent; back titrated with 0.5 mol/L hydrochloric acid, factor 1.0024; blank 49.80 mL, sample 16.55 mL; each mL ≡ 45.04 mg
(49.80 − 16.55) × 1.0024 × 45.04 = 1,501.2 mg · ÷ 1,502.3 mg × 100 = 99.93 %
0.1 mol/L titrant, molar mass 258.07 g/mol, 3 mol of titrant per mol of substance
0.1 × 258.07 ÷ 3 = 8.602 mg per mL
Common uses
- Calculating and recording a titrimetric assay of an active substance or excipient.
- Back titrations such as saponification-type assays, where the blank minus the sample gives the result.
- Non-aqueous assays with perchloric acid, corrected for the temperature of the titrant.
- Checking replicate agreement against the RSD limit of your procedure.
The calculation
- Volume used = titre − blank for a direct titration; blank − titre for a back titration, because the substance used up part of the reagent the blank still has.
- mg found = volume × factor × mg equivalent to 1 mL of the titrant at its nominal molarity. In a back titration the factor is the one of the titrant in the burette: the reagent added in excess cancels out, since the blank uses the same volume of it.
- Per cent = mg found ÷ mg weighed × 100; on the dried or anhydrous basis × 100 ÷ (100 − loss on drying or water %); as a per cent of the label claim × average unit weight ÷ label claim.
- Equivalent from the molar mass = nominal molarity × molar mass ÷ moles of titrant per mole of substance.
Rules from The International Pharmacopoeia
- Rounding: results are calculated to one decimal place more than the requirement and then rounded — 5 to 9 raises the preceding figure, 4 or less leaves it (General Notices, calculation of results). So 101.9451 % against 98.0–102.0 % becomes 101.95 and then 102.0. Where your pharmacopoeia or SOP rounds only once, straight to the limit's decimals, choose Round once under Rounding: the same result then reads 101.9.
- Quantities: the quantity taken may differ from the stated one by not more than 10 %, and is weighed accurately; the result is calculated from the exact quantity (General Notices).
- Non-aqueous titrants in solvents with a high coefficient of expansion, such as glacial acetic acid: when the titration temperature t2 differs from the standardization temperature t1, multiply the volume by [1 + 0.001 (t1 − t2)] (method 2.6). A blank should generally not exceed 0.01 mL of a 0.1 mol/L titrant for each mL of solvent.
Enter another coefficient if your pharmacopoeia gives one.
Sources
- The International Pharmacopoeia — General Notices (quantities; calculation of results), 2.6 Non-aqueous titration, and the reagents and volumetric solutions section
Limitations
- The equivalent, the limits and the procedure come from the monograph you test against; the tool holds no monographs.
- The factor is taken as given: standardize the titrant first (the Volumetric Solution Standardization Calculator does that).
- Results are compared with the limits as their mean; check whether your monograph or SOP also limits single results.
- Up to six replicates at a time.
Privacy
On this device: nothing is sent
Your entries stay in this browser and are never sent anywhere. The PDF and Excel files are made on your device.
Frequently asked questions
What do I get without a pass?
Without a pass, Pharmacopoeial Titration Assay Calculator shows the method, the limits that apply and the verdict for your input, with the first rows of a list; computed figures stay hidden until the pass. Until you unlock it, the result can’t be downloaded or printed. A Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How is an assay calculated from a titration?
Per cent = (titre − blank) × factor × mg equivalent to 1 mL ÷ mg weighed × 100. The equivalent is the monograph’s "each mL of … is equivalent to … mg" for the titrant at its nominal molarity; the factor corrects for its actual strength.
Why is the blank subtracted the other way in a back titration?
Because you titrate what is left of a reagent added in excess. The blank shows all of the reagent; the sample’s titre is smaller by what the substance used up, so the difference blank − sample is the reagent consumed.
Do I correct a perchloric acid titrant for temperature?
Yes, when it is used at another temperature than the one it was standardized at. The International Pharmacopoeia multiplies the volume by [1 + 0.001 (t1 − t2)], t1 being the standardization and t2 the assay temperature.
How many decimals should the result have?
As many as the limit: The International Pharmacopoeia works to one more decimal, then rounds, 5 to 9 rounding up. Type the limits as the monograph writes them (98.0, not 98) and the report rounds to match; choose Round once if your rules round straight to the limit’s decimals. The RSD is rounded to the decimals of its limit in the same way before it is compared.
What is the factor of a volumetric solution?
Its actual molarity divided by its nominal molarity, found by standardization: a 0.1 mol/L solution that is in fact 0.1012 mol/L has a factor of 1.012.