Ph. Eur. 2.2.48 Raman Spectroscopy: How Raman instruments from Metrohm comply with the 2022 update
29. nov. 2021
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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.
An excerpt from the Ph. Eur. 2.2.48 Raman Spectroscopy chapter says:
Raman spectroscopy is commonly used for qualitative and quantitative applications and can be applied to solid, liquid, and gaseous samples. Raman spectroscopy is a rapid and non-invasive analytical method and can be performed off-line, at-line, on-line, or in-line[…] Raman spectrometers can be situated far from the point of measurement using long-distance optical fibres to collect the Raman signal.
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Tutorials for raw materials inspection and verification
For a look at RMID from start to finish, download our free four-part tutorial series here.
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
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:
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Handheld Raman instruments: MIRA P and NanoRam
All MIRA P 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 (starting in April 2022 for MIRA P). 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.
Response-Intensity Scale
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).
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Handheld Raman instruments: MIRA P, MIRA M-3, and NanoRam series
MIRA P, MIRA M-3, and NanoRam systems are designed for qualitative analysis, not for quantitative purposes. Therefore, this criterion is not a strict requirement for handheld Raman products.
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.
Comparison Procedures
For qualitative methods, additional information for identification has been defined.
Several comparison procedures may be used, and the analyst must document and justify the method used and the specific acceptance criteria that allow a conclusion for identification. The spectra can be compared by either overlaying the spectra (in the whole spectral range or in the region of interest specified in the monograph) or by using mathematical calculations of the software. It is possible for example to perform:
- 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[…]
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While an experienced Raman spectroscopist can certainly compare spectra visually and assess sample validity based on peak location, fluorescence, saturation, and signal-to-noise ratio, the widespread implementation of Raman in the real world means that complex analysis must be done by the device and not the user. Statistical comparison methods are used primarily for identification of unknowns through correlation of a sample spectrum with library spectra. The software performs library searches and returns a Hit Quality Index (HQI) value indicating the level of correlation as defined by a user-defined threshold.
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.
Simplified RMID Model Building – Mira Cal P and Model Expert
Method Development with NanoRam®-1064
Verification, p-values, and Training Sets for the Mira P
Wavenumber accuracy requirements of Ph. Eur. 2.2.48
Verify the wavenumber scale for Raman shifts using a suitable standard that has characteristic maxima at the wavenumbers under investigation, for example an organic substance such as polystyrene, paracetamol or cyclohexane[...]
A minimum of 3 wavenumbers covering the working range of the instrument intended for measurements should be selected.[…]
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This chapter maintains the same requirements for Raman wavenumber accuracy and is consistent with the USP <858> and JP 2.26. All of Metrohm’s handheld Raman instruments meet these requirements. Users are recommended to run performance validation tests at regular intervals using polystyrene or another ASTM Raman shift calibration material.
Download our free White Paper below to learn more about instrument calibration, system verification, and performance validation.
Performance tests for Raman wavenumber accuracy are included the Vision and BWAnalyst softwares for the i-Raman series and other portable Raman products (STRam, QTRam, PTRam), with acceptance criteria in accordance with the pharmacopeial requirements.
Metrohm’s unique way of compliance with Ph. Eur. 2.2.48
Better representation of the material
When using Raman spectroscopy[…] care must be taken to ensure that the measurement is representative. This can be achieved by, for example rotation of the sample, performing multiple measurements on different preparations of the sample, using orbital raster scanning (ORS), increasing the area of illumination by reducing the magnification, by demagnification of the laser beam or by changing the focal length between measurements to scan at different depths.
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ORS™ is Metrohm Raman’s proprietary method for moving the excitation laser in a pattern over a sample in order to collect more representative data from a larger area of the sample, especially on heterogeneous samples. All MIRA and MISA instruments are equipped with ORS.
Learn more about ORS by downloading the related Application Note here.
For more details about how we comply, please check the U.S. Pharmacopeia Raman Chapters Updates page on the B&W Tek website. For more general information, download the General Compliance Statement for MIRA handheld Raman systems.
B&W Tek: U.S. Pharmacopeia Raman Chapters Update
For a more comprehensive look at raw material identification and verification in the pharmaceutical industry, read our related blog post.
Real World Raman: Simplifying Incoming Raw Material Inspection
