ANALYTICAL CHEMISTRY AND ITS ERRORS

Analytical Chemistry

Errors

v     Introduction

v     Accuracy

v     Precision

v     Classification of Errors

v     Determinant errors.

v     Indeterminate errors.

v     Absolute errors.

v     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 = x_i-x₁

            Where x_i 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

E_r =

            When x_i and x_i have the same significant as maintained above. Relative error is generally expressed as percent or parts per thousand (PPT)

                        E_r = x100%               or         Er = x1000 ppt