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AMENDMENTS TO THP 2021 VOLUME II
APPENDIX
1.11H POWDER FINENESS AND SIEVES pp. 854‒856
Replace with the following:
                                                         1.11H POWDER FINENESS AND SIEVES
                                                                                       Powders
      The degree of coarseness or fineness of a powder is differentiated and expressed by reference to the nominal mesh aperture size of the sieves used.
      The following terms are used in the description of powders:
       COARSE POWDER  A powder all the particles of which pass through a sieve with a nominal mesh aperture of 1.70 mm and not more than 40.0 per cent through a sieve with a nominal mesh aperture of 355 μm.
      MODERATELY COARSE POWDER A powder all the particles of which pass through a sieve with a nominal mesh aperture of 710 μm and not more than 40.0 per cent through a sieve with a nominal mesh aperture of 250 μm.
       MODERATELY FINE POWDER A powder all the particles of which pass through a sieve with a nominal mesh aperture of 355 μm and not more than 40.0 per cent through a sieve with a nominal mesh aperture of 180 μm.
       FINE POWDER  A powder all the particles of which pass through a sieve with a nominal mesh aperture of 180 μm.
      VERY FINE POWDER A powder all the particles of which pass through a sieve with a nominal mesh aperture of 125 μm.
      When the fineness of a powder is described by means of a number, it is intended that all the particles of the powder shall pass through a sieve of which the nominal mesh aperture, in µm, is equal to that number.
      When a batch of a vegetable drug is being ground and sifted, no portion of the drug shall be rejected, but it is permissible, except in the case of assays, to withhold the final tailings, if an approximately equal amount of tailings from a preceding batch of the same drug has been added before grinding.
     When the use of sieves is inappropriate, the definition is expressed in terms of the particle size as determined by suitable microscopical examination.
                                                                                       Sieves
     Wire mesh sieves used in sifting powdered drugs are identified by numbers indicating the nominal mesh aperture.
     The sieves should be made of wires of uniform circular cross-section. The wires may be of s tainless s teel or of other suitable material except that plated wire is not permitted. Sieves should conform to the specifications which are concordant with the recommended International standard ISO 3310-1:2000 (E), shown in the following table.

      Calibration and recalibration of tes t sieves is in accordance with the most current edition of ISO 3310-1. Sieves should be carefully examined for gross dis tortions and fractures, especially at their screen frame joints, before use. Sieves may be calibrated optically to estimate the average opening size, and opening variability, of the sieve mesh. Alternatively, for the evaluation of the effective opening of tes t sieves in the size range of 212 to 850 μm,
Standard Glass Spheres are available from the national or international organization, e.g. NIST¹. Unless otherwise specified in the individual monograph, perform the sieve analysis at controlled room temperature and a relative humidity between 20 and 70 per cent.
      CLEANING TEST SIEVES Ideally, test sieves should be cleaned using only an air jet or a liquid stream. If some apertures remain blocked by test particles, careful gentle brushing may be used as a last resort. Washing sieves in hot water is not recommended since the sieves can distort and rupture during heating and cooling. If it is necessary to use water, it should be used at ambient temperature and the sieve dried by first using a volatile water-miscible
solvent to remove the water and then a low-pressure air jet to remove the solvent. This procedure should be carried out in a fume hood or cabinet that conforms to local regulations.
                                                                Method for Determining Powder Fineness
       Place the specified quantity of the test powder upon the appropriate sieve having a closefitting receiving pan and cover. Shake the sieve in a rotary horizontal direction and vertically by tapping on a hard surface for not less than the specified time or until sifting is practically complete. Avoid prolonged shaking that would result in increasing the fineness of the powder during the tes ting. In the case of oily or other powders that tend to clog the openings, carefully brush the screen at intervals during the test. Breaking up lumps that form during the sifting. Weigh accurately the amount remaining on the sieve and in the receiving pan.
       The fineness of a powdered drug or chemical may be determined also by screening through the sieves in mechanical sieve shaker, which reproduces the circular and tapping motion given to testing sieves in hand sifting but with a uniform mechanical action, following the directions provided by the manufacturer of the shaker.

                                                     Method for Determining the Particle Size
        The following method-sieving is used for the determination of particle size in herbal drug powders and topical powders. Sieving generally falls into three main types, manual sieving, mechanical sieving and air-jet sieving. Manual sieving and mechanical sieving are most suitable where the majority of the particles are larger than about 75 µm. For particles smaller than 75 µm, air-jet sieving or other means of agitation may be more appropriate.
       Mechanical sieving methods using mechanical agitation or electromagnetic agitation, and that can induce either a vertical oscillation or a horizontal circular motion, or tapping, or a combination of both tapping and horizontal circular motion is available. Entrainment of the particles in an air stream may be used in air jet sieving.
       The relative humidity of the environment in which the sieving is carried out must be controlled to prevent moisture uptake or loss by the sample. If the substance being examined is known to develop an electrostatic charge, an antistatic agent, such as colloidal silicon dioxide and/or aluminium oxide, may be added at a 0.5 per cent w/w level to minimize this effect.

   1. Manual sieving
       SINGLE SIEVE  Place a quantity of the substance being examined, as specified in the individual monograph, upon the sieve with a specified number or a nominal mesh aperture, in µm, with a close-fitting receiving pan and cover. Shake the sieve in a rotary horizontal direction for
not less than 3 minutes, and gently tap on the sieve frequently in vertical direction. Weigh accurately the amount in the receiving pan, and calculate the percentage.
     TWO SIEVES Place the accurately weighed content of 5 single-dose units or of 1 multiple dose unit upon the upper sieve. Shake the sieve in a left-to-right horizontal direction by
gently tapping on the sieve for 3 minutes. Weigh accurately the amount remaining on the coarser sieve and passing through the finer sieve. Calculate the percentage of the fraction.
   2. Mechanical sieving
       Unless otherwise specified, weigh accurately the test sieves having a 200-mm in diameter and the receiving pan. Place 25 to 100 g of the substance being examined, accurately weighed, depending on the bulk density of the material, upon the top or coarsest sieve whereas the
bottom sieve and cover is assembled with a close-fitting receiving pan. Set the mode and the frequency of agitation, and agitate the nest of sieves for 5 minutes, then weigh accurately each sieve and the receiving pan and determine the weight of substance on each sieve.
     Calculate the percentage. Repeat these steps until the weight on any of the test sieve does not change by more than 5 per cent or 100 mg of the previous weight on that sieve. If less than 5 per cent of the total sample weight is present on a given sieve, the end-point for that sieve is increased to a weight change of not more than 20 per cent of the previous weight on that sieve.
  3. Air-jet sieving
      A single sieve is used at a time. It requires sequential analyses on individual sieves starting with the finest sieve to obtain a particle size distribution. Unless otherwise specified, weigh accurately the test sieve having a 200-mm in diameter. Place 25 to 100 g of the substance being examined, accurately weighed, depending on the bulk density of the material, upon the sieve with a cover. Set the pressure and air-jet for 5 minutes, then weigh accurately the sieve and determine the weight of substance on it. Calculate the percentage. Repeat these steps until the weight on the test sieve does not change by more than 5 per cent or 100 mg of the previous weight on that sieve. If less than 5 per cent of the total sample weight is present on a given sieve, the end-point for that sieve is increased to change of not more than 20 per cent of the previous weight sieve.