Taking NIR Calibrations of Feed Compounds from the Laboratory to the Process: Calibration Transfer between Predispersive and Postdispersive Instruments ELVIRA FERN ´ ANDEZ-AHUMADA,* ,† ANA GARRIDO-VARO, † JOS ´ E E. GUERRERO, † DOLORES P´ EREZ-MAR ´ IN, † AND TOM FEARN § Department of Animal Production, University of Co ´rdoba, Campus Rabanales, N-IV, Km 396, 14014 Co ´rdoba, Spain, and Department of Statistical Science, University College London, Gower Street, London WC1E 6BT, United Kingdom In the context of current demands in the animal feed industry for controls and analyses, the use of instruments that may be applied on the process line has acquired a significant interest. A key aspect is that the calibrations developed for quality control with instruments sited in the laboratory (at-line) must be transferred to instruments that will be used in the plant itself (online). This study evaluates the standardization and the calibration transfer between a grating monochromator instrument (predispersive) designed for laboratory analysis and a diode array instrument (postdispersive) more adapted to process conditions. Two procedures that correct differences between spectra of two instruments were tested: the patented algorithm by Shenk and Westerhaus and piecewise direct standardization (PDS). Although results were slightly better with PDS, both methods achieved good spectral matching between the two instruments, with levels of repeatability similar to that of the grating instrument itself. The calibration transfer was evaluated in terms of the standard error of prediction (SEP), which was considerably reduced after standardization. However, final calibration models to be used in the diode array instrument must contain spectra from both types of instruments to give acceptable prediction accuracy. KEYWORDS: Instrument standardization; calibration transfer; NIRS; compound feeds; diode array instruments; grating monochromator INTRODUCTION Nowadays, the manufacturing process of animal feed com- pounds is governed by extensive legislation and internal control frameworks. Techniques and instrumentation able to carry out control and assessments during the process have become of decisive importance. Worldwide, the animal feed industry has been one of the first industries to implement near-infrared reflectance spectroscopy (NIRS) in the laboratory (1). Large and small feed companies utilize NIRS in their laboratories for the analysis of incoming materials and finished product. This technology offers a number of advantages such as speed of response and nondestruction of the sample, which make it well-suited for meeting current demands of online feed analysis. NIRS has also demonstrated its ability to analyze a range of samples from finely milled products to pellets and granules of different size and shape (2). Recent works have shown the feasibility of this technology for carrying out measurement at the mixing and the final stage when diode array instruments, more adapted to process conditions, are used (3, 4). However, before NIRS can be widely used for feed process control, a number of issues must be tackled. A key issue concerning the implementation of NIRS for feed process control is to demonstrate that the robust, expensive, and large calibration sets already existing for laboratory feed analysis, which were developed during many years of investment by feed industrials, may be used for online analysis. Moving to the process should not involve starting again with the calibration procedure for data collected online as though nothing had been done before. Although there has been much progress in NIR instruments, making them more alike, there still exist differences that make impossible the direct transfer of calibration models from one instrument to other instruments (5, 6). There is clearly a need for procedures to standardize traditional laboratory instruments (i.e., predispersive) with instruments more adapted for online analysis (i.e., diode array). * Author to whom correspondence should be addressed (e-mail g82feahe@uco.es). † University of Co ´rdoba. § University College London. J. Agric. Food Chem. 2008, 56, 10135–10141 10135 10.1021/jf801881n CCC: $40.75  2008 American Chemical Society Published on Web 10/22/2008