Analytical Chemistry
Errors
v
Introduction
v
Accuracy
v
Precision
v
Classification of Errors
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Determinant errors.
v
Indeterminate errors.
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Absolute errors.
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Relative errors
Analytical chemistry
[Errors]
Introduction:
Analytical chemistry is one of the
most important branches of chemistry which deals with the resolution,
separation, identification and determination of the constituents of a gives
sample of maters
The subject falls under 2 categories
1. Qualitative
analysis 2. Quantitative analysis
Accuracy: The
term accuracy is designed as the closeness of (matter) measurement or a set of
measurements to the thick or accepted value.
Accuracy is gradually exposed as
terms of absolute errors & relative errors.
Precision:
The term precision is designed as
the degree of agreement between 2 or more replicate measurements made on a
sample in an identical manner i.e., exactly in the same fashion is known as the
precision of the measurements.
Or
Precession reflects the closeness among replicate measurements
of the same quantity or responsibility of the results.
Errors :
Errors are defined as the numerical
differences between as measured value and the absolute or true value of an
analytical determination.
Classification
of Errors
1. Determinate or constant errors.
2. Indeterminable or random errors
3. Cross errors.
4. Errors in measurements.
5. Other errors.
6. Absolute errors.
7. Relative errors.
Determinate
errors:
These are errors which can be
avoided & whose magnitude can be determined and the measurements rectified
a determinate error is characterized by the fact that it effects to the same
degree the results of a series of determinations these can be classified
depending upon the system measured observer and the instrument classification
of determinant errors. There are classified into following categories.
1.
Personal errors.
2.
Operational errors.
3.
Instrumental & reagent errors.
4.
Metabolic errors.
5.
Additive and proportional errors.
II. In determinant Errors:
These errors are accidental and
quite into intorgiber over which the analyst has no control. These errors are
revealed by the small differences in the successive values of measured quantity
when the measurements are made by the same analyst.
Classification
of in determinant errors.
In determinant errors ca be divided
into 2 classes
1.
Variations within determinato
errors
2.
Erratic errors.
Absolute
errors
The errors in a measured quantity
may be represented either as absolute errors or as relative errors. The
absolute error E in a measurement is expressed as
E = xi-x1
Where xi is the measured
value and it is the true (accepted) value for the given measurement.
Relative errors:
The relative errors Er in a
measurement is expressed as
Er = 
When xi and xi
have the same significant as maintained above. Relative error is generally
expressed as percent or parts per thousand (PPT)
Er = 
x100% or Er = x1000 ppt
x100% or Er = x1000 ppt
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