Near-infrared analysis of fennel (Foeniculum vulgare Miller) on different spectrometers--basic considerations for a reliable network.

The aim of this study was to investigate the accuracy and transferability of near-infrared (NIR) calibrations for estimating the content and composition of the volatile fraction in fennel fruits (Foeniculum vulgare Miller) as an example of medicinal and spice plants. A master calibration with spectra obtained on a scanning monochromator was generated using 345 samples from three different harvests (1997-1999). A subset of 70 samples from 1999 was also measured on a dispersive grating and a scanning diode array system to gain an insight into the influence of sample presentation and scanning techniques. For all instruments, calibrations with standard errors in the range of the reference method were achieved. Furthermore the influence of storage on NIR spectra and, additionally, the potential of transferring spectra between both scanning monochromators was studied.