Methods of minimizing errors in chemical analysis involve careful calibration of apparatus, running blanks to account for impurities, using control determinations with standard substances, employing independent analytical methods for comparison, and performing parallel or duplicate determinations. Accuracy refers to how close a measurement is to the true value, while precision describes the agreement between repeated measurements of the same quantity. Significant figures indicate the certainty of measured values and help to properly calculate and report results.

1. Methods of minimizing Errors
• 1) Calibration of apparatus :
• All apparatus like weights, flasks, burettes and pipettes
should be calibrated.
• The appropriate corrections applied to the original
measurements.
• In some case errors cannot be eliminated.
• Apply a correction for that effect.
• e.g An impurity in a weighed precipitate may be determined
and its weight deducted.

3. • 2) Running a blank determination
• It is carried out as a separate determination the
sample being omitted, under exactly the same
experimental conditions as employed in the actual
analysis of sample.
• The object is to find out the effect of the impurities
introduced through the reagents and vessels.
• 3) Running a control determination :
• Determination carried out as nearly as possible
identical experimental conditions upon a quantity of
a standard substance which contains the same
weight of the constituent.

4. • 4) Use of independent methods of analysis :
• Determination of strength of HCl both by titration
with solution of a strong base and by precipitation
and weighed as AgCl.
• If the results obtained by the two radically different
methods are consistent. It is highly probable that the
values are correct within small limits of error.
• 5) Running parallel determination :
• It is as a check on the result of a single
determination and indicate only the precision of the
analysis.

5. • The values obtained should not less than three parts
per thousand.
• If larger variation is there then it must be repeated
until satisfactory concordance is obtained.
• Duplicate/ triplicate determination is suffice.
• A known amount of the constituent being is added
to the sample which is then analyzed for the total
amount of constituent present.
• The difference between the analytical results for
samples with the recovery of the amount of added
constituent.
• If the recovery is satisfactory our confidence in the
accuracy of the procedure is enhanced.

6. • 6. Standard addition:
• a known amount of the constituent being is added
to the sample which is then analyzed for the total
amount of constituent present.
• The difference between the analytical results for
samples with and without added constituent gives
the recovery of the amount of added constituent.
• If the recovery is satisfactory our confidence in the
accuracy of the procedure is enhanced.

7. Definition of Accuracy
• Accuracy:
• How close you are to the actual value.
• it is the degree of agreement between the measured value
and the true value.
• Calculated by the formula:
• % Error = (YV – AV ) X 100 / AV
• where YV is Your measured value and AV is the accepted
value .
• An absolute true value is rarely known.
• so the term accuracy refers to how near the observed value is
to true value.

8. Definition of Precision
• Precision is defied as the degree of agreement between
replicate measurements of the same quantity.
• It is the repeatability of a result.
• So, the term precision refers to nearness between several
measurements of the same quantity.

9. • Accuracy and precision may be demon stared by
shooting at a target.
• accuracy is represented by hitting the bulls eye ( the
accepted value)
• Precision is represented by a tight grouping of shots(
they are finely tuned)

11. • For example : the measured density of water has become
more accurate with improved experimental design,
techniques and equipments.
• for example: if a student measured the room width at 8.46 m
and the accepted value was 9.45 m what was their accuracy?
• Using the formula:
• % error= (YV- AV) X 100 / AV
• Where YV is the student’s measured value and AV is the
accepted value.

12. • since YV= 8.46M AV= 9.45m
• % error = (8.46- 9.45) X 100 /9.45
• = -0.99 X100 /9.45
• = -99/9.45
• = -10.5%
• note that the meter unit cancels during the division
and the unit is % . The (-) shows that YV was low.
• The student was off by almost 11% and must re-
measure.
• percent error is used to estimate the accuracy of a
surement.
•

13. • Percent error will always positive
• what is the percent error if the measured density of titanium
(Ti) 45g/cm3 and the accepted density of Ti is 4.50 g/cm3?
• Accepted error is =/- 5%
• value from -5% up to 5% are acceptable
• value less than -5% or greater than 5%must be remeasured

14. Significant Digits
• Generally, significant figures may be defined as—“All
digits* that are certain plus one which contains
some uncertainty are said to be significant figures”.
• Examples:
• (a) Burette Reading: Burettes are mostly graduated
with the smallest graduation as 0.1 ml; hence, while
taking the burette reading the figures 6.3 ml can be
read off with ample certainty. However, the second
place of the decimal is normally estimated by
arbitrarily sub-dividing the smallest division into 10
equal parts. Consequently, the final burette reading

15. • of 6.32 ml essentially contains three significant figures,
of which two are certain, and one with some
uncertainty.
•
• (b) Measuring Weights: In the two measured
quantities : 4.7350 g and 4.0082 g the zero is a
significant figure ; whereas, in the quantity 0.0065 kg
the zeros are not significant figures. Thus, in the latter
instance the zeros only serve to locate the decimal
point and, therefore, may be eliminated completely by
proper choice of units, e.g., 6.5 g. Moreover, the first
two numbers do have five significant figures, whilst
0.0065 only has two significant figures.
•

16. Rule 1:
all non-zero numbers are significant
e.g. 5489.213 ……. 7 significant digits.
Rule 2:
All zeros located between non-zero numbers
are significant
e.g. 0.08006 ………. 4 significant digits
Rule 3:
E.G 0.00004 ……… 1 significant digit
Rule 4: Trailing zeros
zeros that are located to the right of a value
may or may not be significant
e.g. 1000.0ml ………….4 significant digits
e.g. 1000ml ………………1 significant digit.

17. Course outcomes :
• Pharmaceutical Analysis deals with the fundamentals of
analytical chemistry and principles of electrochemical analysis
of drugs.
• Objectives:
• Upon completion of the course a student shall be able to
understand –
• the principles of volumetric and electrochemical analysis
• carry out various volumetric and electrochemical titrations
• Develop analytical skills

18. • Thank you !!