Lecture 1 - Equipment Flashcards
What are the basics of using a prescription balance?
- beam on knife edge or torsion
- every pharmacist needs one
- sensitivity represented by SR
Describe the concept of the sensitivity requirement
= weight that will cause a distinct change
- SR of 6 mg is req. for a prescription balance (will move 1 unit on index plate)
- capacity is 120 g
How does the sensitivity requirement relate to weighing error?
3 ways:
- % error:
- (% error = (error of measurement/quantity desired, x 100%) - If sensitivity of the balance is known:
- % error = (sensitivity/quantity desired, x 100%) - Can calculate the lowest weighable quantity (LWQ):
- (sensitivity/% error tolerated, x 100%)
How is weighing error calculated?
% error = (error of measurement/quantity desired, x 100%)
error of measurement = MV-DV
How would you calculate the least weighable quantity (LWQ) with a 5% or less error?
LWQ = sensitivity/% error tolerated, x 100%
Describe the technique of trituration to be able to accurately obtain weights of materials below the LWQ with a 5% or less accuracy
= grinding a drug in a mortar with a pestle
goal: to reduce particle size/blend powders (also may be referring to a blended mix of powders & the dilution of a potent drug with an inert diluent powder)
allows removal of an aliquot (weighable quantity) which will have the desired quantity of drug with acceptable accuracy
*any substance being weighed has to be larger than the LWQ for the balance
Describe the concept of geometric dilution & trituration to obtain homogeneity when blending powders
geometric dilution = when a small amount of material is mixed with a larger amount of SOLID or SEMI-SOLID material
- start with small quantity & then use a small quantity of the larger quantity 1st
trituration = can obtain homogeneity because it can also refer to a blended mix of powders & the dilution of a potent drug with an INERT DILUENT POWDER
What are mortars and pestles?
used for small scale comminution (a process to reduce particle size)
made of glass or porcelain
What is the difference between mortars and pestles?
glass - for soft powders, liquid incorporation or semi-solids (aka ointments); good for coloured material & volatile oils
glazed porcelain - rougher (good for trituration), good for coloured material & volatile oils
porcelain - for comminution of crystalline material & for primary emulsions
Describe the process of levigation & what is the purpose of the process
= process of mixing powder with small amount of liquid (levigating agent) in which the powder is INSOLUBLE to make a smooth paste (aka wetting powder)
agent aids in wetting of powder
purpose: reduce particle size & break down aggregates
often done with flexible spatula on a glass slab
Spatulas can be made of stainless steel or plastic. When should steel NOT be used with?
- materials like iodine or strong acids
- materials with harmful trace amounts of metals
- drugs or material that oxidize easily (ex: phenol)
Primarily USED for levigation of powders prior to incorporation into semi-solids (cream or ointments)
When is volumetric glassware used?
to measure EXACT quantities of liquids (‘to deliver’ (TD) (ex: pipettes) or ‘to contain’ (TC) (ex: cylindrical graduates & volumetric flasks)
When are pipettes used?
to measure volumes SMALLER than 5 ml
When should syringes be used?
sizes range from 0.5-60ml (good accuracy; 2 types: parenteral & oral)
When should a volumetric flask used?
to prepare specific volumes (1ml-5000ml)
