Figure 9.4
Variation of relative error with absorbance.
Constant instrumental error 1%. Curve A:
photovoltaic detector. Curve B:
photomultiplier detector.0.8 are subject to a rapidly increasing relative error. The minimum in the error curve for instruments
with photomultiplier detectors is 0.86 because the instrumental reading error dT is proportional to T1/2.
The curve rises more gradually at high absorbances thereby extending the useful working range to at
least 2. Spectrophotometric measurements normally have a relative precision of 1–5%.
Each of the major techniques of molecular spectrometry, including mass spectrometry, will now be
examined in more detail. Exercises in the interpretation of spectral data in relation to the identification
and structural analysis of organic compounds are given at the end of the chapter.
9.1—
Visible and Ultraviolet Spectrometry
Summary
Principles
Absorption of electromagnetic radiation in the visible and ultraviolet regions of the spectrum resulting
in changes in the electronic structure of ions and molecules.
Instrumentation
Filter-photometer or spectrophotometer incorporating prism or grating monochromator, phototube
photomultiplier or diode array, glass, quartz or plastic cells.