Purpose
These traceable reference materials can be used to qualify Mid IR - FTIR spectrophotometers for wavelength accuracy over an operating range of 540 cm-1 to 3125 cm-1 (3.2 µm to 18.5 µm). One version of the product can also be used to qualify the resolution of a Mid IR instrument as required by some pharmacopoeias and for the wavelength qualification of ATR (Attenuated Total Reflectance) measurements in the Mid-IR. Another version has additional certified peaks in the NIR region.
Description and Discussion
Starna reference RM-1921/38 consists of a 38µm polystyrene film mounted in a card holder. 14 certified peaks (arrowed in spectrum below) are available for wavelength qualification purposes. The calibration values are traceable to NIST SRM 1921b.
| NOMINAL WAVENUMBER VALUES (cm-1) | |||||||||||||
| 539 | 842 | 907 | 1028 | 1069 | 1155 | 1583 |
1601 |
1943 |
2849 |
3001 |
3026 |
3060 |
3082 |
The absorption minima and maxima at A and B, C and D can be used to qualify resolution according to pharmacopoeia requirements (EP/JP). This material can also be used for the Wavelength Qualification of ATR (Attenuated Total Reflectance) instrumentation.
Typical spectra
Note: Pharmacopoeia compliance
Using this reference material, a MIR spectrophotometer may be judged to be pharmacopoeia compliant for the certified parameters if the following criteria are met:
European Pharmacopoeia compliance
The difference between the absorption minima at 2870 cm-1 and the maxima at 2849.5 cm-1 is greater than 0.3 (absorbance) and the difference between the absorption minima at 1589 cm-1 and the maxima at 1583 cm-1 is greater than 0.08 (absorbance). The latest revision of EP 2.2.24 cites the use of 38 µm polystyrene for the wavelength qualification of ATR (Attenuated Total Reflectance) instruments in the Mid-IR region.
Japanese Pharmacopoeia compliance
The depth of the trough from the maximum absorption at about 2850 cm-1 to the minimum at about 2870 cm-1 is not less than 18% transmittance and that from the maximum at about 1583 cm-1 to the minimum at about 1589 cm-1 is not less than 12% transmittance.
US Pharmacopeia compliance
A wavenumber tolerance of +/- 1.0 cm-1 is allowed on the position of the following 3082.21 bands; 3060.0, 2849.5, 1942.9, 1601.2, 1583.0, 1154.5 and 1028.3 cm-1.
TGA Australia compliance
TGA allows the use of either BP/EP or USP as appropriate.
An alternative reference material, RM-1921/65, in addition to the 14 peaks in the MIR, has additional peaks on the NIR suitable for wavelength qualification. It is not, however, suitable for Pharmacopoeia resolution compliance measurements, Eight peaks (arrowed in spectrum below) are available for wavelength qualification purposes. The calibration values are traceable to NIST SRM 2065.
| NOMINAL WAVENUMBER/WAVELENGTH VALUES | ||||||||
| cm-1 | 3064 | 3647 | 4039 | 4250 | 4335 | 4608 | 5952 | 8749 |
| nm | 3264 | 2742 | 2476 | 2353 | 2307 | 2170 | 1680 | 1143 |
Note: The values given here are for guidance only. Because the absorption bands are asymmetric, measured values will be spectral bandwidth dependent. The Calibration Certificate accompanying each Starna Mid IR-FTIR Reference gives actual values measured at a bandwidth of 1.00 cm-1, and only these certified values should be used for instrument qualification. Values for the NIR Reference are measured at a resolution of 0.4 nm. On request, Starna can provide certified values at other bandwidths.
Catalogue Number
| Catalogue Number | |
| Starna Mid IR-FTIR Polystyrene Reference, 38 µm | RM-1921/38 |
| Starna Mid IR-FTIR/NIR Polystyrene Reference, 65 µm | RM-1921/65 |
| Starna Mid IR-FTIR Polystyrene Reference for ATR, 38 µm | RM-1921/38/ATR |
| Starna Mid IR-FTIR Polystyrene Reference for ATR, 38 μm, 3 x 9 cm strip | RM-1921/38/ATR/3x9 |