A method is described for providing rapid on-line analyses of chemical
compositions such as chemical process streams, utilizing near-infrared
(NIR) spectroscopy in combination with chemometrics. In the method, for
each type of analysis to be conducted, a database is provided by
analyzing a series of samples using standard laboratory analytical
procedures, utilizing the results as reference values to establish
quantitative calibration models from NIR spectroscopy using chemometric
techniques and storing this information in a computer database. An NIR
spectroscopic system is also provided comprising a transflectance or a
transmittance probe coupled via fiber-optic cables to a stable white
light source and a spectrograph. The probe is inserted into a test sample
or chemical process stream to be analyzed, a stable white light of
selected wavelength range is beamed to the probe and the spectra obtained
on the spectrograph are recorded. Finally the spectra obtained are
correlated to the reference data stored in the computer to obtain a rapid
measurement of the analysis desired.