The European Pharmacopoeia (Ph. Eur.) is a single reference work for the quality control of medicines. Ph. Eur. contains norms, suggests analytical methods, and lists many properties that define quality control (QC) during the production of medicines, the raw materials used, and the instruments required to perform such tests. These official standards are legally binding in several countries – not only in Europe, but worldwide.
Raman spectrometers—especially handheld and portable instruments—are increasingly used for QC of medicines and raw materials (RMID). Instrument interfaces are user-friendly, requiring little technical expertise, and they provide flexible sampling options for most sample types with rapid, non-destructive measurements.
Metrohm’s Raman systems exhibit great flexibility—from see-through to standoff to immersion sampling.
An excerpt from the Ph. Eur. 2.2.48 Raman Spectroscopy chapter says:
Technological developments and their increasing adoption in the pharmaceutical industry prompted a revision of Ph. Eur. 2.2.48 which ensures the reliability of Raman results. The updated chapter 2.2.48 was published in the Ph. Eur. Supplement 10.7 (October 2021) and will ultimately take effect in April 2022.
While much of the Ph. Eur. 2.2.48 chapter has remained the same, the latest revision features:
- new requirements for spectral resolution for qualitative Raman analysis using a suitable reference material
- updated requirements for the Raman response-intensity scale
- detailed procedures for the comparison of spectra
We will address these new requirements across our Raman spectroscopy product lines in the rest of this article.
«Spectral resolution is the ability of a spectroscopic system to separate adjacent bands, which makes it possible to characterise complex samples (e.g., brand analysis, crystallinity, polymorphism).
[…] For identity tests, unless otherwise prescribed in a monograph, the spectral resolution must be less than or equal to 15cm-1 (measured in the wavenumber range between 1000cm-1 and 1100cm-1).
The spectral resolution is verified using a suitable reference material. The instrument parameters used for the test, such as laser, slit-width and grating for dispersive instruments and circular aperture […] for FT-instruments, must be the same as those applied for sample measurements. For example record the Raman spectrum of calcium carbonate for equipment qualification CRS, and determine the full width at half height (W1085) of the band located at 1085 cm-1. The spectral resolution (R) using calcium carbonate is then given by the following relation:»
Handheld Raman instruments: MIRA P, MIRA M-3, and NanoRam
All MIRA and NanoRam devices (including both NanoRam and NanoRam-1064) for the pharmaceutical industry are designed and tested to meet stringent resolution requirements. During QC, the resolution of each instrument is tested to be less than 15 cm-1 against a secondary USP (US Pharmacopeia) reference standard of calcium carbonate according to ASTM E2529, which is the same procedure recommended in this newly released Ph. Eur. chapter.
The measured spectral resolution value for each instrument, along with its identifying serial number, is included in the instrument final test report. A certificate or final test report is packaged with the device and sent to the customer. This resolution is fixed by the optical design of the instrument and is stable over time.
Portable Raman instruments: i-Raman series, QTRam, STRam, and PTRam
The instrument resolution for all of Metrohm’s portable Raman instruments from B&W Tek are factory-tested with calcium carbonate and displayed on final instrument test reports. The spectral resolution is dependent on the instrument design and defined for each specific instrument configuration. Depending on the instrument model, the spectral resolution is between 3.5–11 cm-1. Additionally, the instrument control softwares Vision and BWAnalyst have the performance test function that verifies spectral resolution using the 1001.4 cm-1 peak of polystyrene.
Handheld and portable Raman instruments from B&W Tek.
«The verification of the response-intensity scale is principally performed for quantitative methods.
Appropriate acceptance criteria will vary with the application. A maximum variation of ± 10 per cent in band intensities compared to the previous instrument qualification is achievable in most cases. Response calibration may involve the use of white-light standards or luminescent glass (e.g., NIST SRM 2241).»
Handheld Raman instruments: MIRA P, MIRA M-3, and NanoRam series
However, the relative intensity response of MIRA P and NanoRam series instruments is calibrated with a NIST standard SRM calibration material (SRM 2241, SRM 2242) or NIST SRM 2241-traceable calibration standard to achieve better uniformity from instrument-to-instrument.
The NanoRam series instruments have an acceptance criterion for relative intensity response in the instrument performance validation in alignment with Ph. Eur. 2.2.48 and USP<858>. To pass the performance validation, <10% relative intensity error is required using the factory-supplied polystyrene cap.
Portable Raman instruments: i-Raman series, QTRam, STRam, and PTRam
The relative intensity response of these portable Raman instruments is calibrated using a proper NIST standard SRM calibration material to achieve better uniformity from instrument-to-instrument. Additionally, the Vision instrument control software includes the performance test function that verifies the intensities of several Raman peaks of polystyrene relative to its 1001.4 cm-1 peak, to a maximum variation of ±10% compared to the previous instrument qualification.
For qualitative methods, additional information for identification has been defined.
- visual comparison based on band positions and relative intensities unless otherwise specified[…]
- a statistical determination of the similarity between the spectra of the material to be examined and the reference standard[…]
- evaluation by chemometric methods[…]»
Chemometric methods rely on dimensionality-reduction methods that are performed by the software, such as Principal Component Analysis (PCA), where new sample data is compared within a multivariate model created from representative samples. This permits highly accurate verification of known materials according to how well a spectrum fits into the model limits, which are determined by a confidence interval. In the analysis of medicines and raw materials, chemometric methods are used to distinguish the quality and consistency of a material. MIRA P (and its dedicated software, MIRA Cal P) and NanoRam instruments use both statistical and chemometric methods for sample identification and verification based on the needs of the end-user.
For more information, download our free technical and application notes as well as a White Paper below.
Wavenumber accuracy requirements of Ph. Eur. 2.2.48
A minimum of 3 wavenumbers covering the working range of the instrument intended for measurements should be selected.[…]»
Download our free White Paper below to learn more about instrument calibration, system verification, and performance validation.
The Calibrate/Verify Attachment (CVA) shown here is a dual-ended accessory containing a toluene/acetonitrile ASTM standard for calibration/verification of the wavenumber axis and polystyrene for a second wavenumber verification according to Ph. Eur. 2.2.48.
Metrohm’s unique way of compliance with Ph. Eur. 2.2.48
Better representation of the material
Post written by Dr. Melissa Gelwicks (Technical Writer at Metrohm Raman, Laramie, Wyoming), and Dr. Xiangyu (Max) Ma (Handheld Raman Product Manager) and Dr. Jun Zhao (R&D Director) at B&W Tek, Newark, Delaware.