SOLUTIONSGrade: 3

lec: 2Dr. Rozhan Arif Mohammed

TIU

FACULTY OF PHARMACY

PHARMACEUTICAL TECHNOLOGY I

2020-2021

Outline

Solution

• Definition

• Classification of solution

• Factors affecting Solubility

• Dissolution Rate

DEFINITION

In pharmaceutical term,

solutions are "liquid

preparations that contain one

or more chemical substances

dissolved in a suitable solvent

or mixture of mutually miscible

solvents".

• Dilute Solutions: A solution containing relatively small quantity of solute as compared with the amount of solvent.

• Concentrated Solution: A solution containing large amount of solute in the solution than that in dilute solution.

• Saturated solution is one where the concentration is at a maximum -no more solute is able to dissolve at a given temperature.

• Super Saturated Solution: A solution that contains relatively larger amount of solute than that required for saturation and it is obtained by heating and adding more and more solute.

Pharmaceutical solutions may be classified according to their intended uses into:

Oral solution Otic solution Ophthalmic

solution

Nasal solution (e.g. normal

saline nasal drop)Topical solutions

Classification

Pharmaceutical solutions can be classified according to their composition into:

Syrups: are aqueous solution containing sugar.

Elixirs are clear, sweetened hydro-alcoholic solutions intended for oral use and are usually flavored to enhance their palatability.

Spirits : are alcoholic or hydro-alcoholic solutions of volatile substances. (solutions of aromatic materials if the solvent is alcohol)

Aromatic waters: They are clear aqueous solutions prepared from volatile oils, the solvent is water. Aromatic waters are not the therapeutically potent because of the very small proportion of active ingredient present in them.

Classification

• Tinctures are solutions prepared by extracting active constituents from crude drugs are termed tincture or fluid extracts dissolved in alcohol or in a hydro alcoholic solvent.

tinctures may also be solutions of chemical substances.

• Injections are certain solutions prepared to be sterile and pyrogen free and intended for parenteral administration.

Types of Solutions

Solution of Solid in Liquid

Most of true solutions are example of solid in liquid solution.

Factors Affecting Solubility of Solid in Liquid

a. Endothermic system: most chemicals absorb heat when

they are dissolved and are said to have a positive heat of

solution, resulting in increased solubility with an increase in the

temperature, NH4NO3.

b. Exothermic system: a few chemicals have a negative

heat of solution and exhibit a decrease in solubility with a

rise in temperature e.g. methyl cellulose, NaOH and

Ca(OH)2.

c. Neither exothermic nor endothermic system: which

means that the solubility of the compound at low temperature

is the same when the temperature is high e.g. NaCl.

1. Temperature: the effect of temperature is

not always the same, there are three different cases:

Factors Affecting Solubility of Solid in Liquid

2. Effect of molecular structure of solute and solvent.

• The more nearly solute and solvent are alike molecular structure the greater the solubility of one in the other.

• In general it may be stated that the polar solvents like water will dissolve salts and other electrolyte readily.

• Ex: Water solubilizes NaCl by surrounding the ions of NaCl in such way that –ve center of H₂O close Na+ ion and +ve center of H₂O close to Cl-

• On other hand, non polar liquids are required for non polar solutes.

• Polar liquids may act as solvent when solute are capable of H-bound formation with solvent e.g. water and alcohol of low m.wt.

As the m.wt of alcohol increased, resulted in decrease polarity and decrease the solubility in water.

Steps of Solubility Process

1)Energy needed to separate solute-solute molecules:

Solute Liberation of molecule from solute

must overcome IMF or ion-ion attractions in solute – requires energy, ENDOTHERMIC

2) Energy needed to separate solvent-solvent molecules:

Solvent Creation of a hole in the solvent

Separation of Solvent – must overcome IMF of solvent particles – requires energy, ENDOTHERMIC

Steps of Solubility Process

3) Energy will be give or liberated when solute interact with solvent.

+

Solubility takes place if energy liberate in step 3 is larger than the energy needed in step 1 and 2.

Interaction of Solute & Solvent – attractive bonds form between solute particles and solvent particles – “Solvation” or “Hydration” (where water = solvent) – releases energy, EXOTHERMIC

(- ∆H)

Factors Affecting Solubility of Solid in Liquid

3. Effect of nature of solute: the solutes suffer from polymorphism, hydrates, solvates.

Polymorphism: it is a phenomenon that the compound exists in more than one form which has the same chemical structure but different physical properties like melting point, solubility, absorption and therapeutic activity.

Some polymorph is inactive, so pharmacist should aware about this phenomenon.

ex: chloramphenicol shows polymorphism, it exists in more than one polymorph; one active and other not active.

Factors Affecting Solubility of Solid in Liquid

4. Effect of pH on solubility:

• The pH of medium is important for certain compounds such as weak acid and weak base; it affects the degree of dissociation and the ratio of ionized to unionized form of the compound.

• The ionized form of drug is more soluble than unionized form in water, this affect on absorption and excretion rate.

Effect of pH on Solubility

• The solubility in water of weak organic acids such as barbiturates and sulfonamides is increased as the pH increased by addition of base.

• The solubility in water of weak organic base (alkaloids and local anesthetic) increase as the pH decrease by addition of acid due to the formation of water soluble salts.

Factors Affecting Solubility of Solid in Liquid

5. Effect of addition of other substances:

• Solubility of slightly soluble electrolyte will decrease upon addition of other salt with common ion, but increase if the adding substance form soluble complex with it, as with the addition of potassium iodide to iodine solution

• Sometimes the solubility non-electrolyte increases upon addition of other substance as with the addition of non-ionic surfactant e.g. tween or span to volatile oil in water. Ex. most volatile oils such as peppermint, rose and citrus oils are only very slightly soluble in water but they may be solubilized by the use of certain nonionic surfactant.

Expression of solubility Solubility could be expressed in various ways:

• Quantity per quantity: mg/mL, g/L

• Percentage: % w/w, % w/v and % v/v

• Parts: g/mL

• Molarity: mol/L (of solution)

• Molality: mol/kg (of solvent)

• Normality (N): gram equivalent of solute/ liter solution

The approximate solubility of official substances are indicated by the use of the following descriptive terms:

Rate of Dissolution

• Dissolution is the process where a solute dissolves in a solvent to form a solution.

• Rate of dissolution: it is the speed at which the solute goes into solution it's unit is equal to unit of concentration/ unit of time = ΔC/Δt= mg/ml/min.

• Solubility is the capacity of solute to be dissolved in a given amount of solvent at a given temperature to form saturated solution

Factors Affecting Rate of Dissolution

1.Particle size of the substance: decreasing the particle size by comminution, the surface area will increase, and the rate of dissolution will increase also. The finer the powder, the greater the surface area, which comes in contact with the solvent, and the more rapid the dissolving process.

2. Temperature: the rate of dissolution increases when the temperature increased because increasing the collisions between the solvent and the solute.

3. Agitation: the greater the agitation, the more unsaturated solvent pass over the drug and faster the formation of the solution. In other word, increases the interaction between the solute and the solvent.