Tapped Density Apparatus: Example SOP for Operation and Calibration

In short: A tapped density tester settles a powder in a graduated cylinder by repeated, standardised taps so that bulk and tapped density can be calculated. This example SOP covers operation, a tap-count calibration check and records, and points to the harmonised pharmacopoeial method (USP <616> and Ph. Eur. 2.9.34). Adapt it to your instrument and quality system.

1. Objective

This example SOP describes handling, operation and calibration of a bulk/tapped density apparatus in the Quality Control laboratory.

2. Scope

It applies to the tapped density tester in the Quality Control laboratory. Menu steps below are typical of a programmable, microprocessor-controlled tester and differ between models, so the instrument manual prevails for key presses.

3. Responsibility

• Analyst / section head: follows the SOP and completes the usage log and test records.
• Head of Quality Control (or designee): ensures implementation and timely calibration.

4. Principle of the test

Bulk density is the mass of an untapped powder divided by its apparent unsettled volume. Tapped density is the mass divided by the volume after the powder has been mechanically tapped until the volume stops changing appreciably. The harmonised pharmacopoeial texts (USP <616>; Ph. Eur. 2.9.34; JP 3.01) were accepted as interchangeable under ICH Q4B Annex 13.

For the graduated-cylinder method, the current harmonised text describes in outline: about 100 g of powder, weighed to 0.1 per cent, poured gently into a dry 250 mL cylinder readable to 2 mL. If 100 g would give an untapped volume outside 150 to 250 mL, a different mass is used and reported; for untapped volumes of 50 to 100 mL a 100 mL cylinder readable to 1 mL may be used and reported. The untapped volume is read, then the cylinder is tapped 10, 500 and 1250 times, reading the volume each time. If the 500- and 1250-tap readings differ by no more than 2 mL (1 mL for the 100 mL cylinder), the 1250-tap volume is the tapped volume; otherwise tapping continues in further increments (for example 1250 taps) until successive readings agree within that limit. Fewer taps may be used for some powders when validated. The drop height must be reported with the result.

The harmonised text gives two settings for the graduated cylinder: tapped Method 1, nominally 300 ± 15 taps per minute from a height of 14 ± 2 mm (250 mL cylinder of 220 ± 44 g on a 450 ± 10 g support), and tapped Method 2, a fixed drop of 3 ± 0.2 mm at nominally 250 ± 15 taps per minute. The chapter was revised in this layout, so check that the method number in your specification and instrument programme matches the current text.

Always follow the method in the approved specification for the material.

5. Procedure

5.1 Preliminary checks

1. Check the instrument is clean and free of dust; wipe with a soft, lint-free cloth.
2. Confirm calibration status and that the cylinder is the size required by the method.
3. Connect to mains and switch on using the rear power switch.

5.2 Setting up a programme (example for a menu-driven tester)

1. After the start-up screen, press Enter and choose Prog, then Add/Edit to create a new programme number.
2. Enter the sample name and select the test method (for example USP).
3. Select the procedure type (for example USP-I, II or III as listed on the instrument), the cylinder volume (100 or 250 mL) and the tap-count mode.
4. Enter the tap counts for each reading stage and return to the main menu.

5.3 Running a test

1. Choose Run, optionally View the programme first, then select the programme number and enter the sample identification.
2. Enter the weighed sample mass. Record the initial (untapped) volume in the cylinder.
3. Start the run. At each tap-count stage, read and enter the volume.
4. Continue until the end-point required by the method is met.
5. Calculate: bulk density = mass / initial volume; tapped density = mass / final tapped volume, in g/mL.
6. Switch off the mains after use.
7. After the test, dispose of the powder as per the site’s waste procedure (for example as a slurry in water if the material is safe to do so) and clean the cylinder.
8. Fill the instrument usage log each time the instrument is used.

6. Calibration

Frequency (example in-house criterion): quarterly, and after repair. Written calibration procedures, schedules and records are expected under US FDA 21 CFR 211.68 and 211.160(b)(4).

Tap-count check: set the instrument to 25, 50 and 100 taps in turn and compare the counted taps with the tap number shown. Acceptance (example in-house criterion): the counted number equals the set number.

If the instrument fails, tag it “Out of calibration – do not use” and assess results since the last good check.

7. Records

Keep the usage log, calibration data sheet (Annexure I) and test records. Retain GMP records for at least 1 year after the expiry date of the respective product batch (EU GMP Part I, Chapter 4, §4.11; 21 CFR 211.180(a)), or longer if local law or the marketing authorisation requires.

8. Training and distribution

• Trainer: Head of Quality Control. Trainees: section heads, analysts, officers.
• Controlled copies: Quality Assurance and Quality Control; original with Quality Assurance.

9. Annexure

Annexure I: Calibration test data sheet.

Related reading

• Calibration, verification of performance and qualification of QC instruments
• SOP for maintenance of laboratory instruments
• Records maintenance in the quality control laboratory

Frequently asked questions

What is the difference between bulk and tapped density? Bulk density uses the powder’s unsettled volume; tapped density uses its volume after standardised tapping. Their ratio is used to judge flowability (Hausner ratio, Carr index).

Why must drop height be reported? Different drop heights and tap rates can give different settled volumes, so results are only comparable when conditions are stated.

Can fewer taps be used? The pharmacopoeial text allows fewer taps only when validated for the material.

Abbreviations

QC: Quality Control; SOP: Standard Operating Procedure.

References

• USP General Chapter <616> (revised harmonised text titled Bulk Density of Powders, official 1 August 2025).
• European Pharmacopoeia 2.9.34 Bulk density and tapped density of powders (current edition).
• Pharmacopoeial Discussion Group harmonised text, Bulk density of powders (published by PMDA, pmda.go.jp).
• ICH Q4B Annex 13, Bulk Density and Tapped Density of Powders General Chapter (Step 4, 7 June 2012; it evaluated the earlier harmonised texts).
• US FDA, 21 CFR 211.68, 211.160(b)(4), 211.180(a); EudraLex Volume 4, Part I, Chapter 4, §4.11.
• Instrument manufacturer’s user manual.