Test 2: Solutions Flashcards
(38 cards)
Contamination
Microbes grow in all conditions – most typically 37 degrees C, pH 7
Yeasts and molds in sugar and glucose solutions
Prevention
Hygienic laboratory
Frequent disinfection
Minimize Traffic
Refridgeration
Laminar flow hoods
USP microbe free water for preps (presterilized?)
Initial removal of air from chamber
Pulsed Vacuum
Dynamic Vacuum
Heating Sterilization
A condensate trap at bottom of chamber
Dynamic steam
Post-sterilization phases
Vacuum and time-controlled vacuum maintenance
Cooling by circulating cold water in the jacket
Cooling by spraying water on the load
Ampule tightness with fast vacuum
Spontaneous cooling
Ampule tightness test with dye solution penetration.
Chemical Cold Sterilization
- Ethylene Oxide
- Hydrogen Peroxide
- Hydrogen Peroxide plus steam
- Formaldehyde
Partition Coefficient (K)
Describes how drug will partition between a
non-polar organic phase and a polar water
phase.
K= [HA]o / [HA]
Partition Coefficients and Drug Solubility
– Used to indicate relative lipophilicity of drug
molecules.
– Affects drug solubility, permeability,
bioavailability, and drug binding.
– Most models describe partition coefficient
using octanol - water system.
Partitioning and Extraction of Drugs
Partitioning is the ability of a compound to distribute in two immiscible
systems.
It is of paramount importance, as many pharmaceutical processes such
as absorption from the gastrointestinal tract after oral administration,
diffusion across skin and other epithelia, distribution following entry into
systemic circulation, extraction and isolation of pure drugs after synthetic
manufacturing or from crude plant sources, formulation of a stable dosage
form (emulsion, suspensions, etc) and assay of plasma concentrations are
all based on partitioning phenomenon.
All drugs traverse one or more biological membranes from the time they
are administered until they are eliminated.
Biological membranes are made of protein and lipid materials, but they act
primarily as lipid barriers.
Passive diffusion is the predominant mechanism by which many drugs are
transported, and thus the lipophilic nature of the molecules is important
Transport/Permeation of Drugs
Transport of drug molecules from dosage form to target sites often involves several partitioning
processes. For example, in oral dosage form, followed by dissolution in gastrointestinal (GI) tract, the
drug has to partition between GI fluid and the inner GI membrane, followed by a second partitioning
between the outer GI membrane and systemic circulation before it will reach the target organ. Similarly,
the drug has to partition between its vehicle and skin before the efficacy of a drug molecule can be
achieved following topical application on skin
Formulation of drugs
Partitioning may be a factor in the stability of finished dosage forms where both oil and water phases
exist, for example, in emulsion systems. Antimicrobial preservatives must be present in the aqueous
phase of an emulsion to prevent spoilage. If the preservative chosen partitions into the oil, then additional
preservatives may be needed to maintain an adequate water phase concentration. (This problem
becomes more complicated if the preservative is a weak acid, HA, whose partitioning is pH dependent.)
Industrial processes
Many manufacturing processes involve extracting desirable (or undesirable) substances from a liquid
phase with another immiscible liquid. Such processes depend upon partitioning and permit one to obtain
purer drugs and chemicals.
Analytical procedures
Often these procedures involve an extraction or partitioning step to obtain the desired substance in a
system where it can be analyzed. HPLC (high performance liquid chromatography) is the most widely
used procedure for assaying drug concentrations in biological fluids and is fundamentally dependent
upon a partitioning step.
Partitioning as a function of pH
Most pharmaceuticals are either weakly acidic or weakly basic.
Weak electrolytes exist in un-ionized forms in octanol or lipid
phase
In aqueous phase, both unionized and ionized forms exist in
equilibrium
Therefore partition co-efficient K can be calculated as described
below:
The characteristics of colligative properties are:
- Colligative properties are related and a change in any one of them will
be reflected in the corresponding changes in the others. - A given colligative property of equimolar solutions of electrolytes and
nonelectrolytes will not be identical - Colligative properties of different solutes in a solution are additive
Boiling Point Elevation:
Normal boiling point is defined as the temperature at which
the vapor pressure of the liquid becomes equal to the
external atmospheric pressure (760 mm Hg). The boiling
point of a solution containing a nonvolatile solute would be
higher than the pure solvent because the solute would lower
the vapor pressure of the solvent. The increase in boiling
point can be written as T – T0 = Tb. The ratio of the
elevation of boiling point, Tb, to the lowering of vapor
pressure, p, is approximately a constant at 100°C.
Freezing Point Depression
The normal freezing point of a compound is defined as the temperature at
which the solid and liquid phases coexist under an external pressure of 1
atm.
In general, solutions have a lower freezing point than the pure solvent
If a solute is dissolved in a liquid, the vapor pressure of the liquid solvent is
lowered below the solid solvent.
Then the temperature will drop to re-establish equilibrium between the liquid
and solute.
Thus the freezing point of the solution is always lower than that of the pure
solvent.
The depression of the freezing point of a solution with respect to the pure
solvent is analogous to boiling point elevation
Both pure solid and pure liquid phases of the solvent can coexist with their
vapor, and therefore, both phases have a non-zero vapor pressure.
In solution, solvent co-exists with its vapor, so, at the freezing point of a
solution, the solvent in the solution and the solvent in the solid (which
is composed only of solvent) must co-exist.
Osmotic Pressure:
Water Concentration: Concentration of water in a solution
depends upon the number of solute particles in the solution, not
on their chemical composition
Osmotic pressure: Is defined as the pressure required to offset
the movement of solvent through a semi-permeable membrane
from a dilute aqueous solution to a more concentrated one.
Van’t Hoff Equation: V = nRT
= Osmotic pressure in atmospheres
V is volume of solution in litres
n is the number of moles in solute
R is the universal gas constant equal to 0.082 1 atm mole-1K-1,
Vapor Pressures of Solutions
– Vapor pressure of the system is influenced by
the mole fraction of components.
– Systems can be classified as ideal or nonideal.
Vapor Pressure Lowering
– Addition of a solute lowers the vapor pressure
of the solvent.
– Can be calculates using the molal
concentration of the solute.
Boiling Point Elevation
Addition of a solute to a solvent results
in a solution of higher boiling point that
the pure solvent.
–To calculate this, you need molal
concentration of the solute and the
ebullioscopic constant, Kb.
Freezing Point Depression
Addition of a solute to a solvent results in a
solution of lower freezing point that the pure
solvent.
– To calculate this, you need molal
concentration of the solute and the cryoscopic
constant, Kf.
Osmotic Pressure ()
Free energy of solvent in solution is less that
free energy of solvent in its pure form
– Solvent moves from high free energy state of
pure solvent to lower free energy state of
solution.
Colligative Properties of Electrolytes
Can be obtained by modifying equations with
the van’t Hoff factor (i).
– Factor represent the number of ions
generated per molecule.
