Pharmaceutics

Dissolution Calculator

Absorbance readings → average → concentration → correction factor → corrected concentration → amount dissolved and % drug release, with every step shown.

Tablet / drug information

Drug / dosage form (optional)

Printed on the lab record.

Label claim (drug per dosage unit)

Dissolution medium volume (V)

e.g. 900 mL in each vessel.

Sample withdrawal volume (Vs)

Volume removed at each time point.

Dilution factor (DF)

Unitless. 1 = sample measured undiluted; 10 = 1 mL made up to 10 mL.

Calibration equation

Y = a + bX — Y = absorbance, X = concentration, a = intercept, b = slope

Intercept (a)

Slope (b)

AU/(µg/mL)

Concentration unit (X)

Y = a + bX(Y = absorbance, X = conc. in µg/mL)

Open calibration tool

Time points

Time | B1 … Bn absorbance | Average absorbance — add or remove time points as your practical needs.

Absorbance readings per time point

1–6 readings (B1…B6). Every visible reading is required.

Sampling times and absorbance readings
#	Time(min)	B1(AU)	B2(AU)	B3(AU)	B4(AU)	Average absorbance(AU)	Remove
T1						—
T2						—
T3						—
T4						—
T5						—
T6						—
T7						—

Load an example data set (you can edit every value)

Correction method: practical-sheet (previous corrected concentration)

First time point: no previous withdrawal, so CF = 0 and corrected concentration = concentration. At every later time point CF = (Vs / V) × previous corrected concentration, and corrected concentration = current concentration + CF.

This tool uses only that method. For a different correction, use the Cumulative Drug Release Calculator.

Laboratory calculation card

Enter the tablet data, the calibration equation and every absorbance reading to calculate the dissolution profile.

Average Y = (B1 + B2 + B3 + B4) / 4

X = (Y − a) / b · C = X × DF

CF = (Vs / V) × previous corrected concentration (CF = 0 at the first time point)

Corrected concentration = current concentration + CF

Amount dissolved (mg) = corrected concentration (mg/mL) × V (mL)

% Drug release = (Amount dissolved / Label claim) × 100

Y is the average absorbance, a and b are the intercept and slope of the calibration line, Vs is the sample withdrawal volume and V the dissolution medium volume. A concentration in µg/mL, mg/L, µg/L or g/L is converted to mg/mL as its own step before the amount is calculated.

Worked example: four time points, two readings each

Illustrative values. A 250 mg tablet is tested in 900 mL of medium. At 10, 20, 30 and 45 min a 5 mL sample is withdrawn, diluted 1 in 10 and read twice. The calibration line in the same medium is Y = 0.0021 + 0.0312X (X in µg/mL). Set 'Absorbance readings per time point' to 2 and use four time points.

Label claim: 250 mg
Medium volume V / sample Vs: 900 mL / 5 mL
Dilution factor: 10
Calibration a, b (µg/mL): 0.0021, 0.0312
10 min (B1, B2): 0.312, 0.318
20 min (B1, B2): 0.488, 0.494
30 min (B1, B2): 0.592, 0.586
45 min (B1, B2): 0.641, 0.647

10 min — average, concentration, dilution
Y = (0.312 + 0.318) / 2 = 0.315 AU X = (0.315 − 0.0021) / 0.0312 = 10.0288 µg/mL C = 10.0288 × 10 = 100.288 µg/mL (first point: CF = 0)
10 min — amount dissolved and % release
Amount = 100.288 µg/mL × 0.001 × 900 mL = 90.2596 mg % release = 90.2596 / 250 × 100 = 36.10 %
20 min — correct for the 5 mL already removed
Y = 0.491 → X = 15.6699 → C = 156.699 µg/mL CF = (5 / 900) × 100.288 = 0.557158 µg/mL Corrected C = 156.699 + 0.557158 = 157.256 µg/mL
20 min — amount and % release
Amount = 157.256 × 0.001 × 900 = 141.53 mg % release = 141.53 / 250 × 100 = 56.61 %
30 and 45 min — same steps
30 min: C = 188.109, CF = 0.873644, corrected 188.983 µg/mL → 170.084 mg → 68.03 % 45 min: C = 205.737, CF = 1.0499, corrected 206.787 µg/mL → 186.108 mg → 74.44 %

% drug release: 36.10 % (10 min), 56.61 % (20 min), 68.03 % (30 min), 74.44 % (45 min)

The correction is small here (about 0.5 % of the concentration per sample, because 5 mL is 1/180 of the medium) but it grows with every withdrawal. Whether 74.44 % at 45 min meets the specification is decided by the Q value and stage criteria in the monograph or product specification, not by the profile alone.

Common mistakes

Forgetting the dilution factor. The calibration gives the concentration in the cuvette; the vessel concentration is that value × DF.

Leaving the concentration in µg/mL when multiplying by the medium volume in mL. µg/mL × mL gives µg — convert to mg/mL first, or the % release comes out 1000 times too high.

Using a calibration line prepared in a different medium or at a different wavelength from the dissolution samples.

Applying the withdrawal correction at the first time point. Nothing has been removed before the first sample, so CF = 0.

Reporting % release from one vessel as if it were the batch result. Dissolution tests use several vessels, and the acceptance stages are defined per unit and on the mean.

Assumptions and limitations

This tool applies only the practical-sheet correction, CF = (Vs / V) × the previous corrected concentration. Some manuals instead add (Vs / V) × the sum of all earlier measured concentrations; the two give slightly different later values, so use the method your practical specifies (the Cumulative Drug Release Calculator offers other corrections).

It assumes the medium volume V stays constant because each withdrawn sample is replaced with fresh medium.

The calibration line is assumed to be linear over every absorbance read; a reading above the top standard is an extrapolation.

It calculates a single release profile. Profile comparison (for example the f2 similarity factor) and S1–S3 acceptance testing are separate steps.

Calibration Curve CalculatorBuilds the Y = a + bX line this tool needs and sends it here.Cumulative Drug Release CalculatorIf your practical uses a different withdrawal-correction method.Dissolution Rate Constant CalculatorTo go from a release profile to a dissolution rate constant.

References

United States Pharmacopeia–National Formulary. General Chapter <711> Dissolution. Rockville (MD): USP.
U.S. Food and Drug Administration. Guidance for Industry: Dissolution Testing of Immediate Release Solid Oral Dosage Forms. Rockville (MD): FDA; August 1997.
Aulton ME, Taylor KMG, editors. Aulton's Pharmaceutics: The Design and Manufacture of Medicines. 6th ed. Edinburgh: Elsevier; 2022.

Common questions

Each sample withdrawn removes some dissolved drug from the vessel. The practical-sheet correction adds back (Vs / V) × the previous corrected concentration, so later concentrations are not underestimated.

Nothing has been withdrawn before the first sample, so there is no drug to add back: its corrected concentration equals its concentration.

It multiplies the concentration read from the calibration equation (C = X × DF), because the solution in the cuvette was diluted from the withdrawn sample. Every later step is linear, so applying it at the end would give the same answer.

Usually a reading error, a wrong dilution factor, or a concentration unit that does not match the calibration curve (for example µg/mL entered as mg/mL). Check those before reporting it.

Yes. Open this tool from that calculator's Dissolution button, or press “Import saved calibration” here — the intercept, slope and unit land in the fields, where you can still edit them.

Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy