Peak® Spectroscopy Software Conformity Index

Mis-labeling or contamination of raw materials can be very costly. Conformity testing establishes standards to ensure quality.

Conformity Index, also known as Conformity Test, applies a past/fail test to raw materials, intermediates, and finished products.

While QC Compare is also a pass/fail test, QC Compare works well for Mid-IR (MIR) spectra. Conformity Index is especially useful for Near-IR (NIR) spectra because NIR spectra do not have the 'fingerprint' that Mid-IR spectra do.

For Conformity Index, reference spectra of acceptable lots of a material are collected and used to establish pass/fail thresholds at each wavelength in the spectra. An average of the reference spectra is calculated, and the standard deviation of absorbance values at each wavelength is calculated. This yields an average spectrum and a standard deviation spectrum. A confidence band is established at each wavelength using the average value plus or minus the standard deviation.

A new sample will pass the test if its spectrum lies within the threshold. Any deviation in spectral intensity beyond the threshold will cause the sample to be rejected.

When a sample spectrum is tested, the absolute value of the difference between the sample and the average of the reference spectra is calculated. This residual is then divided by the standard deviation spectrum. The maximum value of this relative deviation is the Conformity Index of the sample spectrum, which is compared against the threshold.

Pass / Fail Algorithms

Four different pass / fail tests are available. In each case, only the values within the selected analysis wavelength ranges are used.

  • Max CI

    The sample's maximum CI value is calculated and compared to the CI threshold.

  • Sum 1

    Values above the CI limit are added and then divided by the number of points in the wavelength ranges.

  • Sum 2

    The values above the CI limit are added and then divided by the number of points above the CI limit.

  • Distance Match (%)

    The percentage of the number of points above the limit is divided by the total number of points.