Calibration Transfer from Sample Cell to Fiber-Optic Probe

Abstract

A calibration transfer method, piecewise direct standardization (PDS), was applied to a set of two-component samples measured on the same UV-visible spectrometer with the use of a cuvette cell with a 10-mm pathlength and a fiber-optic probe with a 2-mm pathlength. Piecewise direct standardization proceeds by determining a structured transformation matrix using the spectra of a few samples measured with both devices. This transformation matrix can then be used to transform any spectrum measured on one device to that obtained on another device, thereby making the calibration model transferable between devices. We used the spectra measured in a cuvette as the standard set and transferred the calibration model obtained for these spectra to spectra measured with a 2-mm fiber-optic probe on the same instrument. The total standard error of prediction (SEP) for the fiber-optic probe was 5.84 before the calibration transfer and 1.87 afterwards. Spectra were also processed by taking the Fourier transform prior to the calibration transfer. The 512 data points in each spectrum were compressed to 32 terms, starting with the first term after the dc offset. This processing reduced the background and the noise. As a consequence, in the Fourier domain, the total SEP was 5.69 before the calibration standardization and 0.79 after the calibration standardization. A calibration transfer was also performed between two fiber-optic probes; the total SEP in the spectral domain was 2.16 prior to the transfer and 1.04 after the transfer, whereas in the Fourier domain the SEP was 1.50 prior to the transfer and 0.77 after the transfer.

A Review of Calibration Transfer Practices and Instrument Differences in Spectroscopy

“…This transformation matrix can then be used to transform any spectrum measured on one device to that obtained on another device, thereby making the calibration model transferable between devices. 30…”

“…This transformation matrix can then be used to transform any spectrum measured on one device to that obtained on another device, thereby making the calibration model transferable between devices. 30 More detailed chemometric improvements to the basic technique of PDS for NIR spectrometric instruments is further described for multivariate calibration transfer in a 1996 paper. 31 One of the more common practical methods applied for field calibration transfers is PDS.…”

Calibration transfer across near infrared spectrometers for measuring hematocrit in the blood of grazing cattle

“…Since introduced by Wang et al, 8 this method has been extensively applied with successful results on a wide range of data sets. 11,[14][15][16][17][18][19][20] Briefly, piecewise direct standardization (PDS) relates the spectral intensity measured by the master to that of the slave in a multivariate manner. In view of the fact that each spectral point on the master would most likely be related to the spectral points at nearby wavelengths on the slave, PDS builds a multivariate model between the spectral intensity of the ith wavelength on the master and the spectral intensities nearby the ith wavelength on the slave.…”

Identification and Characterization of Proteins Involved in Integrin Signaling

“…The process known as calibration transfer or instrument standardization 19,20,21 is a multivariate method used to modify spectra to make them more closely match the response of the instrument at the time the calibration spectra were recorded. In this work, two methods of calibration transfer were investigated:…”