ANALYTAL METHOD PARAMETERS & ERRORS IN ANALYSIS

Accuracy

• Closeness of an actual value to the theoretical / true value

• Expressed as the error in analysis

Absolute error

E = X1 - X2

Relative error

the ratio of the absolute error to the true value, often expressed as a percentage. It indicates the size of the error in relation to the actual value.

E = X1 - X2 / X2 × 100

X1

actual value

X2

true value

Precision

• Closeness of the actual value of 2 or more test results to each other

• Expressed as std deviation

Robustness

capacity to remain unaffected by deliberate variations in methods

Specificity

ability to assess the analyte in the presence of other substances

Sensitivity

ability to discriminate between small differences in analyte concentration

Random error

• Indeterminate Error

• Affects precision

• Small differences in measurements which cannot be identified

• Difficult to eliminate

• Quantifiable through std deviation

Systematic error

• Determinate Error

• Affects accuracy

• Has definite value, or assignable cause

• Can be eliminated

• Quantifiable by difference between mean and true value

SOURCES OF SYSTEMATIC ERRORS

• Instrumental Errors

• Methodological Errors

• Personal / Operative Errors

Instrumental Errors

• Due to imperfection in measuring device or use of instrument under inappropriate conditions

• Ex: Acid / Alkali error

• Corrected by calibration

Methodological Errors

• Due to non-ideal chemical or physical behavior of the reagents and reactions

• Ex: Lack of specificity of some reagents, low purity of reagents

• Corrected by blank determination or standardization

Personal / Operative Errors

• Due to carelessness, inattention, or personal limitations of the analyst

• Ex: Bias or prejudice

• Corrected by self-discipline