Learn how to accurately measure the bulk and tapped density of pharmaceutical powders with this step-by-step guide, following the guidelines set by the United States Pharmacopeia and the In-House. Improve the quality and consistency of your products with a reliable bulk density and tapped density test procedure.

Bulk Density & Tapped Density Test Procedure

1.0     Objective

• • The objective of this General Test Procedure (GTP) is to describe the procedure to be used for Bulk density and Tapped density.

2.0     Principle/Reaction

• • It is a qualitative measuring technique used to find out bulk density to determined by measuring the volume of a known mass of powder sample.

3.0     Requirements: As per USP/IH

• •  Graduated Measuring cylinder

• • Tap density tester

4.0     Bulk Density and Tapped Density as per USP

• • Bulk Density as per USP

• • Measurement Procedure in a Graduated Cylinder:

• • Unless otherwise specified, pass a quantity of material sufficient to complete the test through a sieve with apertures greater than or equal to 1.0 mm, if necessary to break up agglomerates that may have formed during storage.

• • This must be done gently to avoid changing the nature of the material. Into a dry 250 ml cylinder (readable to 2 ml) introduce, without compacting, approximately 100 g of test sample, M, weighed with 0.1% accuracy.

• • Carefully level the powder without compacting, if necessary, and read the unsettled apparent volume (Vo) to the nearest graduated unit. Calculate the bulk density, in g per ml, by the formula –

M/ Vo.

• • Generally repeated determinations are desirable for the determination of this property.

• • If the powder density is too low or too high, such that the test sample has an untapped apparent volume of either more than 250 ml or less than 150 ml, it is not possible to use 100 g, of the test sample and the volume of the cylinder may be modified and the test conditions specified with the results.

• • Select a sample mass having an untapped apparent volume of 150 to 250 ml (apparent volume greater than or equal to 60% of the total volume of the cylinder), the weight of the test samples is specified in the expression of results.

• • For test samples having an apparent volume between 50 ml and 100 ml, a 100 ml cylinder readable to 1 ml can be used, the volume of the cylinder is specified in the expression of results.

• • Tapped Density as per USP

• • Tapped density is achieved by mechanically tapping a measuring cylinder containing a powder sample.

• • After observing the initial volume, the cylinder is mechanically tapped, and volume readings are taken until little further volume change is observed.

• • The mechanical tapping is achieved by raising the cylinder and allowing it to drop under its own weight a specified distance by either of two methods as described below.

• • Devices that rotate the cylinder during tapping may be preferred to minimize any possible separation of the mass during tapping down.

• • USP Method I for Bulk Density / Tapped Density

• • A 250 ml graduated cylinder (readable 2 ml with a mass of 220±44 g).

• • A setting apparatus capable of producing in 1 min, either nominally 250±15 taps from a height of 3±0.2 mm, or normally 300±15 taps from a height of 14± 2 mm.

• • The support for the graduated cylinder, with its holder has a mass of the 450± 10 g.

• • Proceed as described above for the determination of the bulk volume (Vo).

• • Secure the cylinder in the holder.

• • Carry out 10, 500, and 1250 taps on the sample powder and read the corresponding volumes V₁₀,V₅₀₀, and V₁₂₅₀ to the nearest graduated unit.

• • If the difference between V₅₀₀, and V₁₂₅₀ is less than or equal to 2 ml, V₁₂₅₀ is the tapped volume.

• • If the difference between V₅₀₀ and V₁₂₅₀ exceed 2 ml, repeat the increments such as 1250 taps, until the difference between succeeding measurement is less than or equal to 2 ml.

• • Fewer taps may be appropriate for some powder when validated.

• • Calculate the tapped density (g/ml) using the formula m/V_F, in which V_F, is the final tapped volume.

• • Generally, replicated determinations are desirable for the determination of this property.

• • Specify the drops height with the results.

• • If it is not possible to use a 100 g test sample, use a reduced amount and a suitable 100 ml graduated cylinder (readable to 1ml) weighing 130±16 g and mounted on a holder weighing 240±12 g.

• • If the difference between V₅₀₀ and V₁₂₅₀ is less than or equal to 1 ml,V₁₂₅₀ is the tapped volume.

• • If the difference between V₅₀₀ and V₁₂₅₀ exceeds 1ml,repeat in increments such as 1250 taps, until the difference between succeeding measurements is less than or equal to 1 ml.  

• • The modified test conditions are specified in the expression of the results.

• • USP Method II for Bulk Density / Tapped Density

• • Apparatus and procedure:

• • Proceed as directed under Method I except that a suitable mechanical tapped density tester that provides a fixed drop of 3 mm ±0.2 mm at a nominal rate of 250 drops per minute.

• • Measures of Powder Compressibility:

• • The Compressibility Index and Hausner Ratio are measures of the propensity of a powder to be compressed.

• • As such, they are measures of the relative importance of inter particulate interactions.

• • In a free-flowing powder, such interactions are generally less significant, and the bulk and tapped densities will be closer in value.

• • For poorer flowing materials, there are frequently greater inter particle interactions, and a greater difference between the bulk and tapped densities will be observed.

• • These differences are reflected in the compressibility Index and the Hausner Ratio.

• • Compressibility Index — Calculate by the formula:

100 (Vo – V_F)

Vo

Where,

Vo= unsettled apparent volume

V_F = final tapped volume

• • Hausner Ratio — Calculate by the formula:

Vo

V_F

• • Depending on the material, the compressibility index can be determined using V₁₀ instead of Vo. (Note: If V₁₀ is used, it will be clearly stated in the results.)

5.0     Bulk Density and Tapped Density as per In-House (IH)

• • Procedure:

• • Transfers weigh about 100 g of substance being examined for bulk density in the class A measuring cylinder.

• • Carefully level the powder without compacting.

• • Keep the measuring cylinder in the holder of bulk density apparatus set the knob for 500 stokes & start the apparatus.

• • After completion of 500 stokes, remove the measuring cylinder and read the volume of substance in terms of CC or ml, by holding the cylinder parallel to the eyesight.

Calculation:

Actual weight of sample/ml  = g/ml