Improvement of a Standard-Free Method for Near-Infrared Calibration Transfer

Previously, a standard-free method using the finite impulse response (FIR) filter was successfully employed to transfer the NIR spectra of caustic brines, analgesics, and terpolymer resins. This paper carries the FIR transfer method one step further, leading to an improved algorithm that makes the transfer more robust and general by avoiding transfer artifacts in the filtered spectra. Investigations of the theoretical aspects and application examples of diffuse reflectance NIR datasets show that in comparison with our previous version the improved method is much easier to use and gives artifact-free transferred spectra. The improved method also compares favorably with other current signal correction methods for calibration transfer. With the additional advantage of not requiring a subset of standards to be measured on main and remote instruments, the proposed method is a very useful alternative for calibration transfer.