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This article in CS

  1. Vol. 31 No. 6, p. 1694-1696
     
    Received: Oct 4, 1990
    Published: Nov, 1991


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doi:10.2135/cropsci1991.0011183X003100060064x

New Standardization and Calibration Procedures for Nirs Analytical Systems

  1. John S. Shenk  and
  2. Mark O. Westerhaus
  1. Dep. of Agronomy, 241 Agric. Sci. & Industries Bldg., The Pennsylvania State Univ., University Park, PA 16802.

Abstract

Abstract

An important objective of a near infrared spectroscopy (NIRS) analytical system is to have consistent predictions across instruments. Standardized instruments produce very similar spectra, but the standardization procedure is expensive and requires trained personnel. In addition, calibrations need to be insensitive to modest changes in sample and room temperature during routine analysis. This paper describes a simplified standardization procedure for monochromators of the same model. The procedure consisted of aligning instruments with a polystyrene standard and adjusting the baselines of spectra with a sealed sample of concentrate. Wheat Triticum aestivum L.) and hay calibration equations were used to evaluate the consistency of NIRS analyses across these standardized instruments. Bias and standard error of difference corrected for bias [SED(C)] for 29 test samples of different agricultural products were acceptable across instruments. Partial least squares was modified to incorporate a repeatability file containing spectra from different instruments and samples at different temperatures, and the equations were recalculated. The equations derived with the repeatability file showed little or no increase in the standard error of calibration. The same equations, however, showed a substantial decrease in standard error of difference across instruments on test samples with temperature varying from 19 to 29.5 °C.

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