Instant Notes: Analytical Chemistry

of rocks, asbestos and to study residual solvents in pharmaceuticals. Mixtures

can be analyzed directly, although chromatographic methods are normally

preferred (see Topics F3–5).

NIR spectrometryhas been used widely for the analysis of agricultural, food

and pharmaceutical products. It is a rapid technique and may be adapted to the

quality control of process streams as, using fiber optics, remote sampling in

industrial environments is possible. One of the most useful NIR methods uses

diffuse reflectance to analyze solid materials. The sample, usually as a powder,

is placed in an integrating sphereand illuminated from an NIR source that

directs radiation onto it.

A typical use of this type of instrument is shown in Figure9, for measuring

the starch, protein, water and oil components of wheat. A similar technique has

been used to quantify separated analytes in samples separated on TLC plates

directly from their NIR spectra and for analyzing the fat, moisture and protein

content of meat. The technique of multivariate analysis (see Topic B5) has

proved most valuable for this type of work.

E11 – Infrared and Raman spectrometry: applications 247

700 1000 1500 2000 2500

2.0

1.5

1.0

0.5

0

Wavelength (nm)

Absorbance

Starch

Protein

Water

Oil

Fig. 9. NIR spectra of wheat components, (offset for clarity); (2000 nm =5000 cm-^1 ).