Lab Equipment and Instruments 

Essential questions 

What selection criteria are applied to the selection of laboratory equipment and instruments?

How to assure proper accuracy and precision of measurements

Laboratory instruments, measurements, and precision

Laboratory instruments are chosen based on several parameters, most important of which are their accuracy and precision. Precision is defined by how close different measured values are to one another, and accuracy represents how close measured values are to the true value. In some cases, true values are the accepted standards, e.g., standard solutions in chemistry. Precision and accuracy of instruments are technical characteristics that are indicated by the manufacturer and can be verified in the laboratory settings.

For a good summary of precision and accuracy of measurements, please watch this video:

https://www.youtube.com/watch?v=-Ue-o_txQAw

If the average measured value made on the same object is different from its true value, the quantitative term that describes this difference is known as bias. Bias can be determined if the same measurement was made by one laboratory and another (reference) laboratory on the same test item with the same make, model, and age of the instrument, under the same conditions.

Bias in can be identified by:

• Calibration of measuring instruments and/or standards by a reference laboratory
• Control the accuracy and limits of standards that are used in the measurements
• Measurement assurance programs that have the object measured in the client’s laboratory after it has been measured in the reference laboratory
• Comparison of measurement results between several laboratories that share reference standards or materials.

• Selection criteria for laboratory instruments and equipment

Laboratory instruments are selected based on several criteria:

1. Technical characteristics, including precision and accuracy of measurements, reliability and longevity of the instrument
2. Maintenance and operational requirements, serviceability and technical support by the manufacturer
3. Frequency of use and predicted tenure of instrument/equipment use
4. Cost of purchase, maintenance, and use
5. Necessity and cost of upgrade

Performance control and calibration

While accuracy and precision of measuring instrument are of paramount importance, bias can be reduced or eliminated by proper instrument calibration.

Calibration is a process of measurement that assigns defined values to the response of the measuring instrument to reference standards, or to a defined measurement process, or to a defined property of the object. Calibration compares a test value or measurement taken by the instrument with reference standards using specific algorithm.

For more information on instrument calibration, please watch the following:

https://www.youtube.com/watch?v=NV1VToAqfXI

Performance control and calibration of laboratory instruments should be performed according to the manufacturer’s recommendations and within the recommended calibration period. Additionally, calibration should be completed before major critical measurements, after questionable measurement results were obtained, and after any event that could result in changes to the accuracy and precision of the instrument. Performance standards for many instruments are established by the ASTM International.

Suggested readings 

Laboratory Testing Standards. ASTM International. https://www.astm.org/Standards/laboratory-testing-standards.html

Betz, J. M., Brown, P. N., Roman, M. C. (2010). Accuracy, precision, and reliability of chemical measurements in natural products research. Fitoterapia, 82(1), 44–52. doi:10.1016/j.fitote.2010.09.011