Why is there no NG11 standard on my internal FT-IR filter wheel?
The legacy FT-IR spectrometers manufactured by Thermo Fisher Scientific prior to compliance with the European and Japanese Pharmacopeia requirements had a 3.0 mil polystyrene standard mounted on the validation filter wheel along with the 1.5 mil NIST traceable polystyrene standard. The 3.0 mil polystyrene standard is used to test the detector linearity based on five totally absorbing peaks in the mid-infrared spectrum for polystyrene. All of the peaks must measure zero percent transmission within a specified tolerance. The peaks locations are defined in the ASTM E1421 protocol method for verifying FT-IR spectrometers. The 3 mil polystyrene standard is not a NIST traceable standard.
As time progressed we found that a more complete detector test based on the requirements of the European and Japanese Pharmacopeia requirements in addition to ASTM E1421-99 which uses an NG11 glass standard. The NG-11 test is a more complete test of the detectors linearity as we select seven locations in the mid-infrared spectrum of the NG-11 standard. The zero gradient calibration points chosen for calibration produce transmittance values of approximately 73% at 3990 cm-1, 14% at 3512 cm-1, 35% at 3031 cm-1, 6% at 2739 cm-1, 17% at 2598 cm-1, 10% at 2473 cm-1 and 0.01% at 2010 cm-1 This test conforms to the pharmacopeia standards using a NIST traceable standard .
This is why some Thermo Scientific FT-IR Spectrometers have an NG11 standard and some do not.