Liquid Measurement
Dr. Amani Elsayed
Learning Objectives
• Differentiate between volumetric/nonvolumetric
and TD/TC glassware or devices.
• Select glassware/liquid measurement devices
which are appropriate for a particular
measurement operation.
• Describe and/or demonstrate the proper
techniques for using pipettes, syringes, and
graduates for measuring and delivering liquids.
Introduction
• The pharmacist is concerned with liquid
measurement from two perspectives.
• She should be concerned with the ability to
accurately measure the components of a
prescription preparation.
• She must be concerned with how the patient
will measure and deliver an accurate dose of a
liquid medication.
Volumentric Glassware and Other Devices
Intended "to Deliver" TD
• Volumetric Pipets
• They are normally used for
the accurate transfer of 1.0,
2.0, 5.0, 10.0, and 25.0 ml
of liquid.
• Mohr pipette
• The Mohr, or graduate
multiple volume pipet, is
graduated from a point near
the tip to the nominal
capacity of the pipet. Thus,
it can delivery multiple
volumes of liquid with good
volumetric precision.
Volumetric Pipets
Mohr pipette
Volumentric Glassware and Other Devices
Intended "to Deliver" TD
• Syringes
• Hypodermic Syringes
• Hypodermic syringes
come in a variety of
sizes.
• They are especially
useful for measuring
and delivering viscous
liquids.
Hypodermic Syringes
Volumentric Glassware and Other
Devices Intended "to Deliver" TD
• Oral Syringes
• Oral syringes are also
available as a device for
accurately providing a
dose of liquid medication
to the patient. They are
especially useful with
children and elderly
adults who frequently
require nonstandard
doses, and for whom
accuracy of dose is most
critical.
Oral Syringes
Volumentric Glassware and Other
Devices Intended "to Deliver" TD
• Graduates
• Graduates are used for
measuring and
transferring liquids in a
manner that is less
precise than with a
pipette.
• As a general rule, a
graduate should be used
which has a capacity
equal to or just exceeding
the volume to be
measured.
Graduated Cylinders
Conical Graduates
Volumentric Glassware and Other
Devices Intended "to Deliver" TD
• Calibrated Medicine Droppers
• Calibrated medicine droppers
are often used to deliver small
doses of liquid medication, 1
ml or less, to the patient.
• In order to maximize accuracy
of dosing of a compounded
solution from a medicine
dropper, the pharmacist must
calibrate the dropper with the
intended solution at the time
of delivery.
Volumetric Glassware Intended "To
Contain"
• Volumetric Flasks
• Volumetric flasks are
used to prepare
solutions of a specific
volume and
concentration.
• Because of their shape,
the pharmacist would
not reasonably expect
them to deliver their
full volume.
Nonvolumetric Glassware and
Devices
• Erlenmeyer Flasks,
Beakers, and Prescription
Bottles
• Erlenmeyer flasks,
beakers, and prescription
bottles are not volumetric
devices and should NOT
be used to measure
liquids.
• "Graduation" marks on
such vessels are only
approximations of liquid
capacity
Erlenmeyer Flask
Beaker
Nonvolumetric Glassware and
Devices
• Teaspoon
• The Teaspoon and the
problem concerning the
actual volume of liquid
contained in a
"teaspoonful" has existed
for many years.
• Despite various
recommendations, the
problem persists.
• Patients continue to selfadminister liquid doses
from spoons which, in all
probability, are far from
standard.
Guidelines for Selecting Liquid Measurement
Devices
• Always select the smallest device (graduate, pipette,
syringe) that will accommodate the desired volume of
liquid. This will minimize the potential for errors of
measurement associated with misreading the scale.
• Use a graduated pipette, syringe, or calibrated dropper
to measure/deliver volumes <1 ml.
• Remember that oily and viscous liquids will be difficult
to remove from graduates and pipettes, and at best
require long drainage time. Consider using a
disposable syringe instead, or better yet, measuring by
weight rather than volume.
Guidelines for Selecting Liquid
Measurement Devices
• Never use prescription bottles, nonvolumetric
flasks, beakers, or household teaspoons as
measurement devices, unless you calibrate it
yourself.
• When small (<5 ml) or very accurate doses are
required, provide the patient with a calibrated
dropper, oral syringe, or similar device to
ensure proper dosing.
Quiz
1) What might you recommend to provide a
parent to improve the accuracy in
administering a dose of ½ tsp. of antibiotic
liquid to infant
A) A 3 ml oral syringe
B) A dosing cup with 2 tsp. graduation mark
C) A dropper with no graduation mark
D) A plastic teaspoon
Quiz
2) An ointment prescription requires 30 ml of
peanut oil. What is the most efficient way to
measure and deliver this viscous oil?
A) 30 ml single volume pipette
B) 50 ml graduated cylinder
C) Calibrated beaker
D) Weight
Quiz
3) The density of peanut oil is 0.915. How much
will 30 ml of peanut oil weigh?
A) 27.45 g
B) 32.79
C) 29.08
D) 30.915
Quiz
4) The following volumes of teaspoon,
tablespoon and dropper are Correct EXCEPT
(more than one answer)
A) Tsp. 15 ml
B) Tbs. 15 ml
B) Dropper (30 drop/ml)
D) Dropper (20
drop/ml)
E) Tsp. 5 ml
F) Tbs. 5 ml