EVALUATION OF TABLETS

1. Size  & Shape: It can be dimensionally described & controlled. The thickness of a tablet  is only variables. Tablet thickness can be measured by micrometer or by other device. Tablet thickness should be controlled within a ± 5% variation of standard value.

2. Unique identification marking: These marking utilize some  form  of embossing, engraving or printing. These markings include company name  or symbol, product code, product name  etc.

3. Organoleptic properties:  Color distribution  must be uniform with no mottling. For visual color comparison compare the color of sample against standard color.
The presence of odor in a batch of tablet  indicates a stability problem  such as the characteristics odor of  acetic acid in aspirin tablet. Presence of odor could  be characteristic of the drug (Vitamin), added  ingredients (flavoring agent) or the dosage form  (film  coated tablet have a characteristic odor) For  chewable tablet presence or absence of specified taste can be checked. A  tablet level of flaws such as chip, cracks, contamination from  foreign solid  substances  (hair,  drops  of oil,  dirt), surface texture (smooth vs rough) and appearance (shining vs dull) may have zero defect.

4. Hardness and Friability: Tablet requires a certain amount of strength or hardness and resistance to friability to withstand mechanical shakes of handling in manufacture, packaging and shipping. Hardness generally measures the tablet crushing strength. The strength of a tablet was determined by following  ways;

(a) By cracking  the tablet between 2nd  and 3rd  fingers  with  the  thumb acting  as a fulcrum. If there is a sharp snap,  the tablet is an acceptable strength.

(b) Tablet hardness can be defined as the force required breaking a tablet in a diametric compression. In this test the tablet is placed between two anvils, force is applied to the anvils, and the crushing strength  that just  causes the tablet to break is recorded.

Generally used Hardness testers are:
(1) Monsanto  Tester
(2) Strong-Cobb  Tester
(3) Pfizer  Tester
(4) Erweka  Tester
(5) Schleuniger  Tester  

Hardness for compressed tablet is 5 to 8 kg.

Friability of  a tablet  can  determine in laboratory  by Roche friabilator. This consist of a plastic chamber that revolves at 25 rpm,  dropping the tablets through a Distance of six inches in the friabilator, which is then operate for 100 revolutions. The tablets are reweighed. Compress tablet that lose less  than 0.5 to 1.0 % of the Tablet weigh are consider acceptable.

5. Weight Variation test (U.S.P.): Take 20 tablet and  weighed individually. Calculate average weight and compare the individual tablet weight  to  the average. The tablet  pass the U.S.P. test if  no more that 2 tablets are outside the percentage limit and if no tablet differs by more than 2 times the percentage limit.

6. Content Uniformity Test: Randomly select 30 tablets. 10 of these assayed individually. The Tablet pass the test if  9 of the 10 tablets must contain not less than 85% and not more than 115% of the labeled drug content and the 10th  tablet may not contain less than 75% and more than 125% of the labeled content. If  these  conditions  are not met, remaining 20 tablet assayed individually and none may fall out side of the 85 to 115% range.

7. Disintegration Test (U.S.P.): The U.S.P. device to test disintegration uses 6 glass tubes that are 3” long;  open at the top and 10 mesh screen at the bottom  end. To test for disintegration time, one tablet is placed  in each tube and the basket rack is positioned in a 1-L beaker of  water, simulated  gastric fluid or simulated intestinal fluid  at 37 ± 20  C such that the tablet remain 2.5 cm  below the surface of liquid on their upward movement  and not closer than  2.5 cm  from  the bottom  of the beaker in their downward movement. Move the basket  containing the tablets up and down through a distance of 5-6 cm  at a frequency  of 28 to 32 cycles per minute. Floating of the tablets can be prevented by placing perforated plastic discs on each tablet. According to the test the tablet must disintegrate and all particles must pass through the 10 mesh screen in the time specified. If  any residue remains, it must have a soft mass.

Disintegration time:

Uncoated tablet: 5-30 minutes
Coated tablet: 1-2 hour

8. Dissolution Test (U.S.P.):

Apparatus-1:  A single tablet is placed in a small wire mesh basket attached to the bottom of the shaft connected to a variable  speed motor. The basket is immersed in a dissolution medium  (as  specified in monograph) contained in a 100 ml  flask. The flask is  cylindrical  with  a hemispherical bottom. The flask  is maintained  at 37±0.5^C by a constant temperature bath. The motor is  adjusted  to  turn at the specified speed and sample of the fluid are withdrawn at intervals to determine the amount of drug in solutions.

TABLET EXCIPIENTS

DILUENT:- Diluents  are  fillers used  to  make required bulk of  the  tablet  when the drug dosage itself is inadequate to produce the bulk. Secondary reason is to provide better tablet properties such as improve cohesion, to permit use of  direct compression manufacturing or to promote flow.

Commonly used tablet diluents:-

1. Lactose-anhydrous and spray dried lactose
2. Directly compressed starch-Sta Rx 1500
3. Hydrolyzed starch-Emdex  and Celutab 
4. Microcrystalline  cellulose-Avicel (PH 101and PH 102) 
5. Dibasic calcium  phosphate dehydrate
6. Calcium  sulphate dihydrate
7. Mannitol  
8. Sorbitol
9. Sucrose- Sugartab, DiPac, Nutab
10. Dextrose

BINDERS & AHESIVES:- These materials are added either dry or in wet- form  to form  granules or to form cohesive  compacts for directly compressed tablet.

Example:

Acacia, tragacanth- Solution for 10-25% Conc.      
Cellulose derivatives- Methyl  cellulose, Hydroxy propyl methyl cellulose, Hydroxy propyl cellulose      
Gelatin- 10-20% solution      
Glucose- 50% solution        Polyvinylpyrrolidone (PVP)- 2% conc.        Starch paste-10-20% solution. Sodium alginate, Sorbitol

DISINTEGRANTS:- Added to a tablet formulation  to facilitate its breaking or disintegration when it contact in water in the GIT.

Example:

Starch- 5-20% of tablet weight.                
Starch derivative – Primogel and Explotab (1-8%)                
Clays- Veegum  HV, bentonite 10% level in colored tablet only.         
Cellulose derivatives- Ac- Di-Sol (sodium  carboxy methyl cellulose)                
Alginate                
PVP (Polyvinylpyrrolidone), cross-linked

SUPERDISINTEGRANTS:- Swells up to ten fold within 30 seconds when contact water.

Example:

Crosscarmellose- cross-linked  cellulose, Crosspovidone- cross-linked povidone (polymer),
Sodium  starch glycolate- cross-linked starch. These cross-linked products swell upto 10n fold with in 30 seconds when in contact with water.

A portion of disintegrant  is added before granulation and a portion before compression, which serve as  glidants  or  lubricant. Evaluation of carbon dioxide in effervescent tablets is also one way of disintegration

LUBRICANTS AND GLIDANTS:-

Lubricants are intended to  prevent adhesion of the tablet materials to the surface of dies and punches, reduce  inter particle friction and may improve the rate of flow of the tablet granulation. Glidants are intended to promote flow of  granules or powder material by reducing the friction between the particles.

Example:

LUBRICANTS:- Stearic acid
Stearic acid salt - Stearic acid, Magnesium stearate, Talc, PEG (Polyethylene glycols), Surfactants

GLIDANTS:- Corn Starch – 5-10% conc., Talc-5% conc.
Silica derivative - Colloidal silicas such as Cab-O-Sil, Syloid, Aerosil in 0.25-3% conc.

COLORING AGENTS:- The use of colors and dyes in  a tablet has three purposes:    

(1) Masking of off color drugs  
(2) Product Identification    
(3) Production of more  elegant product

All coloring agents must  be approved and  certified by FDA. Two forms of colors are used in tablet preparation – FD &C and D & C dyes. These dyes are applied as solution in the granulating agent or Lake form  of these dyes. Lakes are dyes absorbed on hydrous oxide and employed as dry powder coloring.

Example:

FD & C yellow 6-sunset yellow
FD & C yellow 5- Tartrazine                
FD & C green 3-   Fast Green                
FD & C blue 1- Brilliant Blue                
FD & C blue 2 - Indigo carmine  
D & C red 3- Erythrosine 
D & C red 22 – Eosin Y

FLAVOURING AGENTS:- For chewable tablet- flavor oil are used

SWEETENING AGENTS:- For chewable tablets: Sugar, mannitol. 
Saccharine (artificial): 500  time’s sweeter than sucrose.

TAPPED DENSITY

TAPPED  DENSITY:- The  tapped  density  is  an  increased  bulk  density  attained  after  mechanically  tapping  a container  containing  the  powder  sample.   The  tapped  density  is  obtained  by  mechanically  tapping  a  graduated  measuring  cylinder  or vessel  containing  the  powder  sample.  After  observing  the  initial  powder  volume  or  mass,  the measuring  cylinder  or  vessel  is  mechanically  tapped,  and  volume  or  mass  readings  are  taken until  little  further  volume  or  mass  change  is  observed.  The  mechanical  tapping  is  achieved  by raising  the  cylinder  or  vessel  and  allowing  it  to  drop,  under  its  own  mass,  a  specified  distance by  either  of  three  methods  as  described  below.  Devices  that  rotate  the  cylinder  or  vessel during  tapping  may  be  preferred  to  minimize  any  possible  separation  of  the  mass  during tapping down.

Method  A :- The  apparatus  consists  of  the  following:

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

a  settling  apparatus  capable  of  producing,  in  1  minute,  either  nominally  250  ±  15  taps from  a  height  of  3  ±  0.2  mm,  or  nominally  300  ±  15  taps  from  a  height  of  14  ±  2  mm.  The support  for  the  graduated  cylinder,  with  its  holder,  has  a  mass  of  450  ±  10  g.

Procedure

Proceed  as  described  above  for  the  determination  of  the  bulk  volume  (V0).  Secure the  cylinder  in  the  holder.  Carry  out  10,  500  and  1250  taps  on  the  same  powder  sample  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  exceeds  2  ml,  repeat  in  increments  such  as  1250  taps, until  the  difference  between  succeeding  measurements  is  less  than  or  equal  to  2  ml.  Fewer taps  may  be  appropriate  for  some  powders,  when  validated.  Calculate  the  tapped density  (g/ml)  using  the  formula  m/Vf  in  which  Vf  is  the  final  tapped  volume.  Generally, replicate  determinations  are  desirable  for  the  determination  of  this  property.  Specify  the  drop 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  1  ml)  weighing  130  ±  16  g  and  mounted  on  a  holder  weighing 240  ±  12  g.  The  modified  test  conditions  are  specified  in  the  expression  of  the  results.

Method  B

Procedure

Proceed  as  directed  under  Method  A  except  that  the  mechanical  tester  provides  a fixed  drop  of  3  ±  0.2  mm  at  a  nominal  rate  of  250  taps  per  minute.

Method  C

Procedure

Proceed  as  described  in  Method  C  for  measuring  the  bulk  density  using  the measuring  vessel  equipped  with  the  cap.  The  measuring  vessel  with  the  cap is  lifted  50-60  times  per  minute  by  the  use  of  a  suitable  tapped  density  tester.  Carry  out 200  taps,  remove  the  cap  and  carefully  scrape  excess  powder  from  the  top  of  the  measuring vessel  as  described  in  Method  C  for  measuring  the  bulk  density.  Repeat  the  procedure  using 400  taps.  If  the  difference  between  the  two  masses  obtained  after  200  and  400  taps  exceeds 2%,  carry  out  a  test  using  200  additional  taps  until  the  difference  between  succeeding measurements  is  less  than  2%.  Calculate  the  tapped  density  (g/ml)  using  the  formula  Mf/100 where  Mf  is  the  mass  of  powder  in  the  measuring  vessel.  Record  the  average  of three  determinations  using  three  different  powder  samples.  The  test  conditions  including tapping height are specified in the expression of the results.

MEASURES OF POWDER COMPRESSIBILITY

Because  the  interparticulate  interactions  influencing  the  bulking  properties  of  a  powder  are also  the  interactions  that  interfere  with  powder  flow,  a  comparison  of  the  bulk  and  tapped densities  can  give  a  measure  of  the  relative  importance  of  these  interactions  in  a  given powder.  Such  a  comparison  is  often  used  as  an  index  of  the  ability  of  the  powder  to  flow,  for example  the  Compressibility  index  or  the  Hausner  ratio. The  Compressibility  index  and  Hausner  ratio  are  measures  of  the  propensity  of  a  powder  to  be compressed  as  described  above.  As  such,  they  are  measures  of  the  powder  ability  to  settle  and they  permit  an  assessment  of  the  relative  importance  of  interparticulate  interactions.  In  a  freeflowing  powder,  such  interactions  are  less  significant,  and  the  bulk  and  tapped  densities  will be  closer  in  value.  For  poorer  flowing  materials,  there  are  frequently  greater  interparticulate 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:- 100(Vo-Vf)/Vo

where

Vo - unsettled  apparent  volume,
Vf - final  tapped  volume.

Hausner Ratio: Vo/Vf

Depending  on  the  material,  the  compressibility  index  can  be  determined  using  V10  instead  of V0. If V10 is used, it is clearly stated in the results.

BULK DENSITY

BULK DENSITY:- The  bulk  density  of  a  powder  is  the  ratio  of  the  mass  of  an  untapped  powder  sample  and  its volume  including  the  contribution  of  the  interparticulate  void  volume.  Hence,  the  bulk  density depends  on  both  the  density  of  powder  particles  and  the  spatial  arrangement  of  particles  in  the powder  bed.  The  bulk  density  is  expressed  in  grams  per  millilitre  (g/ml)  although  the international  unit  is  kilogram  per  cubic  metre  (1  g/ml  =  1000  kg/m3)  because  the measurements  are  made  using  cylinders. It  may  also  be  expressed  in  grams  per  cubic  centimetre  (g/cm3). The  bulking  properties  of  a  powder  are  dependent  upon  the  preparation,  treatment  and  storage of  the  sample,  i.e.  how  it  was  handled.  The  particles  can  be  packed  to  have  a  range  of  bulk densities  and,  moreover,  the  slightest  disturbance  of  the  powder  bed  may  result  in  a  changed bulk  density.  Thus,  the  bulk  density  of  a  powder  is  often  very  difficult  to  measure  with  good reproducibility  and,  in  reporting  the  results,  it  is  essential  to  specify  how  the  determination was made.

Method  A:- Measurement  in  a  graduated  cylinder

Procedure

Pass  a  quantity  of  powder  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  graduated  cylinder  of  250  ml  (readable  to  2  ml),  gently  introduce,  without compacting,  approximately  100  g  of  the  test  sample  (m)  weighed  with  0.1%  accuracy. Carefully  level  the  powder  without  compacting,  if  necessary,  and  read  the  unsettled  apparent volume  (V0)  to  the  nearest  graduated  unit.  Calculate  the  bulk  density  in  (g/ml)  using  the formula  m/V0.  Generally,  replicate  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  powder  sample.  Therefore,  a  different  amount  of  powder  has  to  be  selected  as  test  sample, such  that  its  untapped  apparent  volume  is  150  ml  to  250  ml  (apparent  volume  greater  than  or equal  to  60%  of  the  total  volume  of  the  cylinder);  the  mass  of  the  test  sample  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.

Method  B:-  Measurement  in  a  volumeter Apparatus

The  apparatus consists  of  a  top  funnel  fitted  with  a  1.0  mm  sieve.  The funnel  is  mounted  over  a  baffle  box  containing  four  glass  baffle  plates  over  which  the  powder slides  and  bounces  as  it  passes.  At  the  bottom  of  the  baffle  box  is  a  funnel  that  collects  the powder  and  allows  it  to  pour  into  a  cup  mounted  directly  below  it.  The  cup  may  be  cylindrical (25.00  ±  0.05  ml  volume  with  an  inside  diameter  of  30.00  ± 2.00  mm)  or  cubical (16.39  ±  0.20  ml  volume  with  inside  dimensions  of  25.400  ±  0.076  mm).

Procedure

Allow  an  excess  of  powder  to  flow  through  the  apparatus  into  the  sample receiving  cup  until  it  overflows,  using  a  minimum  of  25  cm3  of  powder  with  the  cubical  cup and  35  cm3  of  powder  with  the  cylindrical  cup.  Carefully,  scrape  excess  powder  from  the  top of  the  cup  by  smoothly  moving  the  edge  of  the  blade  of  a  spatula  perpendicular  to  and  in contact  with  the  top  surface  of  the  cup,  taking  care  to  keep  the  spatula  perpendicular  to prevent  packing  or  removal  of  powder  from  the  cup.  Remove  any  material  from  the  side  of the  cup  and  determine  the  mass  (M)  of  the  powder  to  the  nearest  0.1%.  Calculate  the  bulk density  (g/ml)  using  the  formula  M/V0  in  which  V0  is  the  volume  of  the  cup  and  record  the average  of  three  determinations  using  three  different  powder  samples.

Method  C:- Measurement  in  a  vessel Apparatus

The  apparatus  consists  of  a  100  ml  cylindrical  vessel  of  stainless  steel.

Procedure

Pass  a  quantity  of  powder  sufficient  to  complete  the  test  through  a  1.0  mm  sieve, if  necessary,  to  break  up  agglomerates  that  may  have  formed  during  storage  and  allow  the obtained  sample  to  flow  freely  into  the  measuring  vessel  until  it  overflows.  Carefully  scrape the  excess  powder  from  the  top  of  the  vessel  as  described  for  Method  B.  Determine  the mass  (M0)  of  the  powder  to  the  nearest  0.1%  by  subtraction  of  the  previously  determined  mass of  the  empty  measuring  vessel.  Calculate  the  bulk  density  (g/ml)  using  the  formula  M0/100 and record the average of three determinations using three different powder samples.

DIFFERENT TYPES OF TABLETS

Repeat action tablet: Sugar coated or multiple compressed tablets are used for this purpose.The core tablet is usually coated with shellac or an enteric polymer so that it will not release its drug in stomach but intestine. 

Delayed action and enteric-coated tablet: This  dosage form is intended to release the drug after some  time delay or after the  tablet has passed one part of the GIT into another. All  enteric coated  tablets are type  of  delayed action  tablet  but all delayed action tablets are not enteric or not intended to produce enteric action. 

Sugar coated tablet: Primary role is  to produce an elegant, glossy, easy  to swallow, widely utilized in preparing multivitamin and multivitamin mineral combination. Sugar coating doubled the tablet weight. Now polymers are used with sugar solution.

Film coated tablet: One type of coated tablet in  which drug is  not required in coating. This is an attractive method within one or two hours. Polymers such as hydroxypropylcellulose, hydroxypropylmethyl cellulose, and colloidal dispersion of ethylcellulose are commonly used. A 30% dispersion of ethyl cellulose is known as aquacoat. Advantage of film  coated over  sugar coated  tablets  is  better mechanical strength and flexibility of the coating, little increase in tablet weight. 

Chewable tablet: These are intended to be chewed  in the mouth before swallowing. Used for large tablet of antacid, bitter or foul testing drugs are not  suitable for this type tablet.

Buccal and sublingual tablet:  These tablets are small, flat and are intended to be held between the cheek  and teeth or in cheek  pouch (buccal tablet) or  below the tongue (sublingual tablet). Drugs used by this  route are for quick  systematic action. The tablets are designed not to be disintegrate but slowly dissolve.

Troches and lozenges:  Used in  the oral cavity to exert local effect in mouth and throat. They are commonly used to treat sore  throat or to control coughing in common cold. They may contain local  anesthetics,  antiseptic,  antibacterial agents, demulcents,  astringent  and  antitussive. The tablets are dissolving slowly over a period of 30 minutes.

Dental cone: These tablets are designed to be placed in the empty socket remaining after tooth extraction. Main purpose is to prevent microbial growth in the socket or to reduce bleeding.

Implantation tablets: Designed for substances implantation to provide prolonged drug effect from  one month to a year, tablets are usually small, cylindrical not more than 8mm length. These methods require special surgical technique for implantation and discontinuation of therapy. Generally used for administration of growth hormone to food producing animal.

Vaginal tablets: These are designed to undergo slow  dissolution and drug release in vaginal cavity. Tablets are wide or pear shaped,  used to antibacterial, antiseptic and astringent to treat vaginal infection.

Effervescent tablets: Tablets are designed to produce  a   solution  rapidly with  the release of carbon dioxide. The tablets  are prepared by compressing the active ingredient with mixture of organic acid such as  citric acid or  tartaric acid and sodium bicarbonate.

Dispersing tablets:  Tablets are intended to be added to a given volume of water to produce a solution of a given drug concentration.

Hypodermic tablets:  These tablets are composed of one or more drugs with watersoluble ingredients. Drug is added to sterile water to prepare sterile solution, which is injectable.

Tablet triturates:  Usually are made from  moist materials  using a  triturate mold, which gives them the shape of cylinder. Such tablet must be completely and rapidly soluble.

Compressed tablets:  Standard  uncoated  tablets are manufactured by  compression. The general methods are by wet granulation,  dry granulation or direct compression, used for rapid disintegration and drug release. Both type of action – systemic effect and local effect.

Multiple compressed tablets:  For incompatible components these are:  

A) Layered tablet- either two  layered (for two components)  or three layered (for three components) tablet.

B) Compressed coated type- either tablet within a tablet or tablet  within a tablet within a tablet.

Tablet  in this category are usually prepared for two reasons

1.  To separate physically or chemically  incompatible  ingredients.

2. To produce repeat action or prolong action product.

Volume and Density Determination Methods Using Manual Laboratory Devices

PYCNOMETRY ( SPECIFIC GRAVITY BOTTLES):- A pycnometer is a vessel with a precisely known volume. Although  a pycnometer is used to determine density  ρ  or specific  gravity,  it measures  volume  V; a balance is used to determine mass  m.  Manual  pycnometers (glassware)  typically  are used to determine the density  or specific gravity  of liquids  by  filling the vessel, then weighing. Density  is  calculated by  ρ  =  m/V  and specific gravity  by  the same equation and dividing  both sides by  the density of water with reference to temperature. First the object containing  the void  is weighed empty. It  is then filled with a  liquid  of known density  and reweighed. The  weight difference  ∆m  is the weight of the liquid  and from  these data, volume  can be calculated by V =  ∆m/ρ. As  will be  explained,  this  process  is used to ‘calibrate’ sample cells used in  mercury porosimetry. Another pycnometer method is to place a quantity  of a dry,  pre-weighed solid sample  in the  pycnometer and fill the rest of the pycnometer with a liquid of known density (typically  water), the weight of  the  pycnometer filled only  with the liquid having  previously been  established. The density  of the sample can be  determined  from  the known density  of the water,  the  weight  of the pycnometer filled only with the liquid, the weight  of  the  pycnometer containing  both sample and  liquid,  and  the weight of the sample.  This is a common  method used in characterizing  soil samples.

HYDROSTATIC WEIGHING ( DISPLACEMENT METHOD):- By  this  method,  the volume  of a solid sample is determined  by  comparing  the weight of the sample in air to the weight  of  the  sample immersed in a liquid of known density. The volume  of the sample is equal to  the  difference in  the  two  weights divided by  the density  of the liquid.  Conversely, if the volume  of a solid object is accurately  known, the density  of the  liquid  can be  determined  by  the loss of weight of the immersed  object.This is the basis for the hydrometer method. If  the sample is porous, one must determine  if the pores are to be included  or  excluded  from the  volume.   If  they  are to be included or the sample will react with  the  displacement medium,  a  sealing  coating  can be applied. If  pore volume  is to be excluded, the liquid must displace the air and completely  fill the  pores. Various pretreatment methods are used including  evacuation and boiling. When  determining  volume  by  directly measuring  the displaced volume,  liquids,  fine particles  or gases can be used as the displacement medium. If  the  sample  material  is porous,  fine  particles will not penetrate into the smaller pores that water  can  enter.  Mercury, being  a non-wetting  liquid, also will not penetrate pores under ambient pressure  as  will wetting  liquids. Gases, Helium  in  particular, will penetrate readily  into very  fine pores.

HYDROMETERS:- A  hydrometer is  a  vertical  float that measures the density  or specific gravity  of  a liquid  or liquid/solid suspension (slurry). The hydrometer,  inscribed  with a graduated scale along  its length, sinks into the  liquid  until  it  has displaced  a volume  of liquid equal in weight to that of the float.  Specific  gravity  or  density  is read directly  from  the inscribed scale at the liquid  surface  after buoyancy  and gravitational forces equalize.

FLOAT-SINK OR SUSPENSION (BUOYANCY) METHOD:-This  method  requires  a liquid of known and adjustable  density  in which the sample is placed. The  density  of the liquid is adjusted until the sample  either  begins  to  sink  or float , or is suspended  at  neutral  density  in the liquid.The  density  of the object is then equated to that of the liquid. This method also is used  to separate materials by  their density.

DENSITY GRADIENT COLUMN:-  A density gradient  column  is a column  of liquid that varies in  density  with height.  A sample is placed in the liquid  and observed to determine at what vertical  level in the column  the sample is suspended.    The  density  of the liquid at that level  is  the density  of the sample, and that value is determined by  standards of known density.

TAP DENSITY AND VIBRATORY PACKING  DENSITY:- These are very  similar methods for  determining the bulk  density  of a collection of  particles under  specific  conditions  of packing.   In  the former case, packing  is achieved by  tapping  the container and in the latter by  vibrating  the container. The particles under test should  not break  up under test conditions.

BULK/ENVELOPE VOLUME BY COATING:- Coating the sample allows  determination of  bulk  volume or apparent volume  of solids while preventing absorption  or reaction with suspension liquids. Penetration of the coating  into the  open  pores  of the sample must be considered. Following  the referenced method  the  mass of the sample is obtained. The  sample  is  dipped into molten wax of known density. After withdrawal, any  air bubbles in the  wax  coating are pressed out, and the coated  sample  is weighed.  The difference in  weight  before  and after  coating  is  the weight of the wax, and dividing  this  number  by  the density  of the wax provides the volume  of  wax  composing  the coating.   The volume  of the coated sample  is determined by  hydrostatic weighing.    From  this volume, the volume  of wax (or other coating)  is subtracted, yielding  the bulk  (or  envelope) volume  of the sample.

VALIDATION OF TEST SURFACE TO EVALUATE CLEANING EFFICACY

SWAB SAMPLING PROCEDURE

1. Pipette out 5 ml of sampling solvent in transport container.

2. Remove a swab from its protective bag using a clean latex hand glove.

3. Avoid touching the swab head to prevent its contamination. 

4. Transfer the swab in transport container (test tube) containing 5 ml of sampling solvent and allow the swab to soak completely. 

5. Take out the swab from sampling solvent and squeeze the tip against inner surface of test tube to remove excess solvent in such a manner that excess solvent drips inside the test tube.

6. Hold the stem of swab without touching the head of the swab.

7. Using one side of moistened swab wipe the test surface of 5 sq. inch with 10 firm horizontal strokes using a clean template. 

8. At the end of each stroke, lift the swab carefully. 

9. Turn the swab over to its other side; wipe the test surface of 5 sq. inch with 10 firm vertical strokes using the template.

10. At the end of each stroke, lift the swab carefully.

11. Hold the stem of the swab without touching the head of the swab and let the swab drop into the transport container. Plug the transport container with stopper and send for analysis after adequately labeling the same.

PROCEDURE FOR MICROBIOLOGICAL EVALUATION

1. Take a sterile swab to sampling point.

2. Mark the swab with (1) Sampling point & (2) Date on outer cover. 

3. Put on the clean latex hand gloves and disinfect the same with 70% IPA. 

4. Take out the sterile swab carefully from the outer cover dip the swab in sterile water and swab the complete selected area (10x10 cm). 

5. Replace the swab immediately inside the cover, close it and send for analysis. Sample should not be hold for a long period exceeding 24 hours

Fo CALCULATIONS

NUMERICAL Fo VALUE

The actual observation obtained during the heat penetration studies at different temperature sensing location are complies in the table and the observed temperature shall be subjected to fo calculation at that particular location the lethality factor calculation is done by using the formula

F0 = dt ∑10(T-121)/z

F0 = dt ∑(sum of lethality factor)

Where,

dt = time interval between successive temperature measurements.

T =observed temperature at that particular time (as actual temperature recoded).

Z  = change in the heat resistance of Geobacillus stearothermophilus

Spores as temperature is changed (10°C or mentioned in COA).

Fo VALUE FOR BIOLOGICAL INDICATORS

The biological F0 value for biological indicator strip exposed during the sterilization can be calculated as follows

               F0 = D121 (log A – log B)

 Where,

 D121 = D Value of the biological indicator at 121°C

 A =experimental biological indicator concentration or spore population.

 B =desired level of sterility (SAL - 10^6)

DESIRED SPORE LOG REDUCTION

Calculate the desired reduction in spore log population by using the formula

SLR Desired = log A – log SAL desired

Where,

A = experimental population of biological indicator

SAL desired = desired level level of sterility (10-6)

ACTUAL SPORE LOG REDUCTION

Calculate the actual reduction in spore population by using the formula

SLR actual  = Fo/D121

Where,

     Fo = Minimum calculated Fo value

     D121 = D value of Biological indicator

HEATING BLOCK VALIDATION

PROCEDURE
   
1. Take 5 calibrated thermometer and give them No. L1, L2, L3, L4, L5 as mentioned in annexure.

2. Keep five thermometer in test tubes at different location inside well of heating block as per location chart enclosed.

3. Operate Heating block as per S.O.P.

4. Compare temperature of each thermometer with respect to temperature adjusted one on heating block  at every 15 minutes interval upto 1 hours.

5. Record the result as per annexure.

ACCEPTANCE CRITERIA

Temperature on display should be within 37°C + 1°C.

The results obtained at all location of heating block should be within 36 to 38°C.

Change the location by placing thermometer in other than previously selected location to cover maximum well during validation in a calendar year.

FREQUENCY

Every month