A spectrophotometer, as an analytical tool is used in almost every type of chemical, biological or life science laboratory. The instrument may range in complexity from a simple single beam instrument, right through to dual beam or complex and sometimes highly automated instruments. Some such instruments may also be part of, or built into a system for in-line or process measurement.
Irrespective of complexity, all spectrophotometric instruments are based on the fundamentals of the Beer-Lambert law. Like all instrumentation they require regular checking and validation to a greater or lesser extent. The parameters tested for spectrophotometers are photometric accuracy (absorbance linearity), wavelength accuracy, bandwidth and stray light. These checks and validation protocols, ensure confidence in all operational and performance matters and are also mandated in many cases by accreditation and regulatory bodies.
These functions are determined by the use of a range of chemical standards. Such standards are formulated to give specific responses, depending on the measurement function being tested. Therefore, it is an imperative that high quality standards be available for performing linearity, wavelength, bandwidth and stray light tests. Such standards should be produced from high quality chemicals, that are fully characterised and should follow the metrological principles that all standards are subject to, including traceability, uncertainty of measurement, accuracy, specification, stability, precision and safety.
High Quality Standards must also be available to the user at a price that is fit for purpose.
There are a number of high-quality producers of such standards. However, the standards produced by Reagecon are most familiar to the authors, so the description of spectrophotometry standards in this paper relate to those available from Reagecon. We believe that the standards described are cutting edge, complete and form the basis of a template to guide the analyst on what to take into account, during the selection process of fit for purpose standards. The narrative and description of what to look for in spectrophotometry standards is preceded by a brief introduction into the science and technology behind spectrophotometry in very simple detail.
2.0 Basic Theory on Spectrophotometry
3.0 Applications of Spectrophotometry Standards
3.4 Stray Light
3.5 Pharmacopoeia Requirements
Other Papers on Measurement Standards
by John Barron