Methods of Expressing Concentration Concentration in Pharmaceutical Sciences

1. Methods Of Expressing Concentration in
Pharmaceutical Analysis
Presented By
Dr.Lingeswara Rao Punati
M.Pharm.,Ph.D
DEPARTMENT OF PHARMACEUTICAL
ANALYSIS
Chennupati Indo American School of Pharmacy
Jonnalgadda, Narasaraopet

2. Methods Of Expressing Concentration in pharmaceutical analysis:
Percentage weight / weight:
Percentage weight in weight expresses the number of grams of solute in 100gm of
product. The concentration of strong acids, available commercially.
e.g: H2SO4 98.0% w/w; CH3COOH 33%w/w etc..
Also expressing the percentage purity of the solid dosage forms such as tablets,
capsules, etc..as percent weight / weight.
Percentage volume / volume:
Percentage volume in volume it expresses the number of milliliters of solute in 100ml
of product
E.g: alcohol 95%

3. • Percentage weight / volume:
It express the number of grams of solute in 100ml of product (i.e 100ml of solution). This is
a common way of specifying solution composition of mixtures of miscible liquids, or
solids in liquids.
e.g : H2O2 solution 5 -7% w/v, BaCl2 solution 10% w/v etc..
Percentage volume /weight:
It expresses the number of milliliters of solute in 100 gm of product.
Usually the strength of solution of solids in liquids are expressed as percentage weight in
volume, of liquids in liquids as percentage volume in volume and gases in liquids as
percentage weight in weight.

4. Parts per million:
When the concentration of solution is expressed as parts per million (ppm), it means
weight in weight unless otherwise specified. Ppm – the number of grams of solute
contained in 106 g of solution.
Molarity:
The molarity of solution expresses the number of moles (gram molecular weight) of
solute contained in 1000ml of solution.
A solution containing 1 mole of solute in each liter of total solution is said to be a one
molar (M) solution.
M = n /v
M = weight of substance x 1
Gram Molecular Weight volume(ltr)

5. Normality:
The normality of solution expresses the number of equivalents (gram equivalent
weights) of the solute in one liter of solution.
Normality = weight of substance x 1
Gram Equivalent weight volume(ltr)
Equivalent weight of acid:
Equivalent weight of the substance is that weigh which contains 1gm of replaceable
hydrogen ion.
GEW = Molecular Weight or formula of acid
basecity of acid

6. Equivalent weight of base:
Equivalent weight of the substance is that weigh which contains 1gm of replaceable
hydroxyl group.
GEW = Molecular Weight or formula of base
basecity of acid
Salt:
Equivalent weight of the substance is that weigh which contains 1gm of replaceable
total number of cation or anion.
GEW = Molecular weight
total no of cation or total no of anion

7. Units:
1 kilogram = 1000 gram
1 gram = 1000 milligram
1milligram = 1000 microgram
1microgram = 1000 nanogram
1 milligram = 10-3 gm
1microgram = 10-6 gm
1nanogram = 10-9 gm
Conversions:
1. Convert w/v to mg/ml
Formula: multiply by 10.
w/v x 10 = mg/ml
To convert 2% w/v to mg/ml
2% w/v x 10 = 20mg/ml
or
2% w/v means 2 grams /100 ml
i.e 2000/100ml = 20 mg/ml

8. 2.Convert mg/ml to w/v:
Formula: mg/ml = % w/v
10
Convert 30 mg/ml to % w/v
30mg/ml = 3% w/v
10
1ml contains 30mg
100 ml contains 30 x 100mg
= 3000mg
= 3gm
= 3 gm/100 ml.
= 3% w/v

9. 3.Convert %w/v to µg/ml
Formula: multiply by 10000
w/v x 10000 = µg/ml.
Convert 2% w/v to µg/ml
2% w/v x 10000 = 20000 µg/ml
2% w/v means 2 gm/100ml
= 2000mg in 100ml
= 20mg /ml
= 20,000 µg/ml

10. Dilutions:
for preparing calibration curves, dilutions have to be prepared from stock solutions. In
dilutions, the following must be observed.
1. Minimum quantity of stock solution is to be used.
2. At any step, dilution should not be more than 5 or 10 times(this is to minimize error
in dilution).
E.g: 1ml to 5ml or 1ml to 10ml can be done, but not 1ml to 100ml.
3.The total volume of solution available should be sufficient for subsequent dilutions.
4.In order to avoid confusion in calculations. It is better to use the following format
Intial volume final volume(concentration/ml)

11. Prepare a calibration curve from 10 to 40 µg/ml. The given stock solution is
1mg/ml (1mg/ml = 1000 µg/ml).
1mg 1ml = (1000 µg/ml) = 1x1000 = 1000 µg/ml
1
1ml 10ml = (100 µg/ml) = 1000 x 1 = 100 µg/ml
10
1ml 10ml = (10 µg/ml) = 100 x 1 = 10 µg/ml
10
2ml 10ml = (20 µg/ml) = 100 x 2 = 20 µg/ml
10
3ml 10ml = (30 µg/ml) = 100 x 3 = 30 µg/ml
10
4ml 10ml = (40 µg/ml) = 100 x4 = 40 µg/ml
10
the above 4 solutions are ready for calibration curve
Prepare a calibration curve from 1 µg/ml to 5 µg/ml using 100mg /100ml stock
solution