While performing analytical measurements in laboratory, various types of errors
may be encountered.
3.1 Types of Laboratory Errors
There are three major errors that may occur in a laboratory:
1.Random errors: Random errors are the errors that arise due to statistical
fluctuations in the observations and lead to inconsistent measurement value of a
constant attribute. A random error is associated with the fact that when a
measurement is repeated, it will generally provide a measured value that is
different from the previous value. Random errors are caused by uncontrollable
variables, which cannot be defined or eliminated. These are errors that may arise
due to bubbles in reagents or reagent lines, instrument instability, temperature
variations, and operator variability, such as variation in pipetting.
2.Systemic errors: Systematic errors cause inaccurate results that are consistently
low or high. This error is reproducible and predictable and can be easily identified
and corrected. These errors are caused by insufficient control on analytical
variables, e.g., impure calibration material, change in reagent lot, change in
calibration, assigning the wrong calibrator values, improperly prepared or
deteriorating reagents, etc. Majorly, systemic errors arise due to three factors:
(a) Instrument errors: Instrument errors are errors associated with instru-
ment functioning. These arise due to powerfluctuations, defect in any
parts of the instrument, temperature variation, or when the instrument is
not calibrated. The instrumental errors can be removed by proper cali-
bration or maintenance of instrument.
(b) Method errors: These are errors that arise due to the use of non-ideal
physical or chemical methods. For example, the speed of reaction,
problem associated with sampling, and interference from side reactions
can lead to such errors. The development and use of proper method can
help to correct these errors.
(c) Personal errors: These are caused by an observer’s personal habits or
mental judgment, wrong judgment of dimensional values, color acuity
problems, etc. It may be accidental or systematic. Proper training and
experience can help to eliminate the personal errors effectively.
3.Gross errors or total analytical error: Such errors arise due to equipment failure
or observer’s carelessness.
The laboratory errors may also be grouped into pre-analytical, analytical, or post-
analytical errors according to time of occurrence.Pre-analytical errorsarise before
the analysis of sample takes place. Common examples of pre-analytical errors are
mismatch of sample and laboratory data, error in presentation of analyzed results,
and delaying in report generation. Theanalytical errorsoccur during analytical
methods and include errors related to expired or spoiled reagents, use of controls or
10 3 Quality Control in Laboratory