Weighing and Measuring Amounts of Ingredients
Session 9: Weighing and Measuring Amounts of Ingredients
Required for Compounding
Total Session Time: 120 minutes
Prerequisites
Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
Activity/
Step Time Content
Method
1 05 minutes Presentation Introduction, Learning Tasks
50 minutes Presentation
2 Buzzing Weighing Amounts of Ingredients
Demonstration
55 minutes Presentation
3 Brainstorming Measuring Volumes of Ingredients
Demonstration
4 05 minutes Presentation Key Points
5 05 minutes Presentation Evaluation
Session X: ———— -(Title)———————- 50
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning tasks and clarify
ASK students if they have any questions before continuing.
STEP 2: Weighing Amounts of Ingredients (50 minutes)
Activity: Buzzing (5 minutes)
ASK students to pair up and buzz on the following question for 2 minutes
ALLOW few pairs to respond and let other pairs to add on points not mentioned
WRITE their response on the flip chart/board
CLARIFY and SUMMARIZE by using the content below
is the common instrument used in weighing different amounts of ingredients required for
compounding.
o Use a balance that is suitable for weighing the required quantity. The maximum
weight that is accurately measured by the balance is determined by multiplying
the smallest scale unit by 200. Never try to weigh quantities exceeding the
capacity of the balance. Check whether the balance and the weights are calibrated
for the SI unit system. If not, make sure the amounts to be weighed are converted
to the same SI unit as in the weighing balance.
o Check the instrument for inaccurate adjustment and sticking by releasing the
beam on a trial swing and observing the movement of pointer over the calibrated
scale (For non-electrical balance)
o When using a non-electrical balance make sure the balance arm can move freely.
This is checked by touching the balance pan with a forceps. Make sure the
balance is in the down or is resting position, before transferring materials or
weights to or from the pans.
o When using a non-electrical balance always use forceps to transfer weights; never
touch weights with your fingers. Put weights back into weight drawer or into their
case immediately after use and close the weight drawer immediately. These
procedures are to avoid corrosion and contamination of the weight and keep them
accurate.
Session X: ———— -(Title)———————- 51
o Never weigh pharmaceutical materials directly on the balance pan. Use a piece of
paper for solids, waxed paper for semisolids, and appropriate vessels for liquids.
Vessels used for liquids requires cleaning after each weighing.
o Use a suitable spatula for transfer of materials to the balance pan. Take care not to
spill any material. Clean immediately after spilling material. The spatula should
be cleaned after each weighing.
o Some pharmaceutical material are corrosive or aggressive. Special containers and
spatulas are sometimes needed.
o After weighing a solid that has to be dissolved in a liquid, it can be washed off
with that liquid.
o Clean the balance thoroughly after use.
Activity: Demonstration (30 minutes)
DIVIDE students in small manageable groups.
PREPARE equipment and materials needed for demonstration
POSITION students so that everyone can see and hear
REVIEW general rules for weighing ingredients using weighing balance with students.
REFER students to the general rules of weighing pharmaceutical ingredients.
DEMONSTRATE the procedure of weighing solid pharmaceutical ingredients for
compounding.
ALLOW one student from each group to do a return demonstration and let others comment on it
CLARIFY and SUMMARIZE
INFORM the students that “every student will practice in the skills laboratory under supervision
until is competent”
Session X: ———— -(Title)———————- 52
STEP 3: Measuring Volumes of Ingredients (55 minutes)
Activity: Brainstorming (5 minutes)
Ask students to brainstorm on the following question:
ALLOW few students to respond
WRITE their responses on the flip chart/ board
CLARIFY and SUMMARISE by using the content below
cylinder), pipettes, and a dropper or syringes.
o Select a measure of a suitable size. Pharmaceutical measures show no scale lower
than the minimum volume they can accurately measure.
o Make sure the scale of the measure is in milliliters (mL), not otherwise. When the
volume is stated in other units, convert the volumes to milliliters (mL)
o Always read the scale at eye level, at the bottom of the liquid surface (meniscus)
as shown on figure 9.1 below. When reading the scale is difficult, hold a piece of
dark colored paper behind the measure.
o Make sure no liquid remains in the measure. It may take some time for liquid to
flow out completely, particularly when you are measuring viscous liquids. For
water and aqueous solutions keep the measure top down for 15 seconds after all
the liquid has flown out, and 2 minutes for syrup and oils.
o Measure should be cleaned and dried after each measurement. Measures should
not be used while they are still wet.
Session X: ———— -(Title)———————- 53
o To prevent contamination of measures with dust, they should be kept upside
down, preferably in a clean cupboard.
o Select an adequately graduated pipette whose capacity is appropriate to the
volume requiring measurement.
o Then draw small volume of the liquid to be measured into the pipette and
thoroughly wet all the internal surfaces of the pipette. Allow liquid to drain and
discard it.
o Carefully fill the pipette to a level slightly above the graduation mark.
o Quickly replace the bulb (or mouth) with your forefinger to stop the liquid from
flowing out. The best way to control the flow of liquid from the pipette is with a
slightly wet fore finger.
o Make sure there are no air burbles in the fluid or on the fluid surface.
o Wipe the outer surface of the pipette clean.
o Hold the tip of the pipette against glass vessel and allow the liquid to flow out
until the bottom of the liquid surface just touches the graduation mark.
o Place the tip of the pipette against the inner wall of the receiving container,
holding the pipette in a vertical position and the container at an angle of about 450
from vertical.
o When the free flow ceases, rest the tip against the wall of the container for an
additional 15 seconds.
o Rinse the pipette thoroughly after use.
o For corrosive and toxic liquids, attach a rubber bulb to the stem of the pipette.
Under no circumstances mouth suction can be used.
Activity: Demonstration (30 minutes)
DIVIDE students in small manageable groups.
PREPARE equipment and materials needed for demonstration
POSITION students so that everyone can see and hear
REVIEW general rules for measuring volumes of ingredients using pipette and measuring
cylinder with students.
REFER students to the general rules of measuring volumes of pharmaceutical
ingredients.
DEMONSTRATE the procedure of measuring volumes of liquid pharmaceutical ingredients for
compounding.
ALLOW one student from each group to do a return demonstration and let others comment on it
CLARIFY and SUMMARIZE
INFORM the students that “every student will practice in the skills laboratory under supervision
until is competent”
Session X: ———— -(Title)———————- 54
STEP 4: Key Points (5 minutes)
is the common instrument used in weighing different amounts of ingredients required for
compounding.
cylinder), pipettes, and a dropper or syringes
surface (meniscus)
weighed or measured.
STEP 5: Evaluation (5 minutes)
compounding?
compounding?
Session X: ———— -(Title)———————- 55
References
Peter Bakker, H. W., Vincent Gooskens, Ben Naafs, Rachel Van der Kaaij, Nicolien Wieringa.
(2012). Dermatology Preparations for the Tropics (2nd ed.).
Pharmaceutical Society of Great Britain., & Pharmaceutical Society of Great Britain. Department
of Pharmaceutical Sciences. (1994). The Pharmaceutical Podex, Principles and Practice
of Pharmaceutics (W. Lund Ed. 12th ed.). London,: Pharmaceutical P.
Senya, S. S., Mwasha, C. Y. S., Muyinga, A. M., Amiri, R. I., & Mauga, E. A. S. K. (2011).
Tanzania Pharmaceutical Handbook (2nd ed.). Dar es salaam: School of Pharmaceutical
Sciences, Institute of Allied Health Sciences, Muhimbili University of Health and Allied
Health Sciences.
Stoklosa, M. J., & Ansel, H. C. (1996). Pharmaceutical calculations (10th ed.). Baltimore:
Williams & Wilkins.
Session X: ———— -(Title)———————- 56
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