Raman spectroscopy is a powerful technique that is being increasingly adopted by the pharmaceutical industry to analyse the molecular composition of solid, liquid, or gaseous samples, and serves as an integral quality control (QC) step along the supply chain. A simple and robust method, Raman spectroscopy requires no sample preparation and is proving invaluable for industry leaders who are looking for ways to evolve their manufacturing and remain competitive.

Continuous manufacturing has become a buzzword in the pharma industry as it offers many benefits over the old ‘stop-and-run’ approach, including shorter production times and reduced costs, particularly over the long term. In addition, this approach improves the quality of the final product while making processing itself more energy efficient. Continuous manufacturing also leads to fewer people being directly involved with the pipeline from start to finish, minimising the risk of human error and ensuring high product consistency. This can make a huge difference, as demonstrated by a study by the Industrial BioDevelopment Laboratory, which revealed more than 20% variability in test results among 16 experienced technicians adhering to the same manual standard operating procedure (1). It is therefore unsurprising that manufacturers are moving towards the implementation of solutions that reduce inter-operator inconsistencies by removing as many manual steps as possible from the production process.

QC is a major part of any pharma manufacturing process – partly because it is so heavily regulated – and continuous production within these workflows requires technologies that allow the assessment of the composition of ingredients and partial products without disrupting the process. Raman spectrometers are ideal for this purpose and are becoming increasingly popular among industry leaders as they can not only help to identify and quantify incoming raw materials, but can also be applied to every stage of the manufacturing process. For example, one common approach is to validate incoming compounds using handheld Raman spectrometers – that can scan the chemicals even through the packaging – and follow up with installing Raman process analysers in-line with the flow for downstream monitoring. This combination eliminates the need for time-consuming tests and a dedicated QC laboratory and, since an average pharmaceutical manufacturing factory spends approximately $40 million per year on QC, this can lead to a significant reduction in costs (2). In addition, streamlining QC in this way helps to get the product to market far quicker by spotting and correcting any issues earlier.

Raman spectroscopy has been around for decades and, although the theory behind this method has not changed, the corresponding technology has evolved greatly throughout the years. Traditionally, a mercury lamp was used as a source of light and the resulting spectrum was caught on a photographic plate after hours – or even days – of exposure.

Modern Raman spectrometers are a far cry from their predecessors and use reliable, stable, inexpensive lasers with narrow linewidths that allow them to truly minimise the frequency variations of the emitted photons. This ensures reliable results and, as Raman-based instruments can now be made small enough to be handheld, they are becoming the technology of choice for many manufacturers; simplifying quality control, enhancing productivity, and reducing the number of interruptions throughout the entire production chain.

Raman spectroscopy gathers information about the chemical structure, phase and polymorphy, crystallinity, and molecular interactions of a substance by analysing how it scatters incoming laser light. The laser beam is delivered to the sample – in either solid, liquid, or gaseous form – using a fiber-optic cable with a probe at its end. The incoming energy causes the molecules to vibrate and scatter the light, which is collected and interpreted by a detector. The scattering can be either elastic, meaning the frequency of the outgoing photon is unchanged, or inelastic, where the energy of the photon shifts up or down. This results in a Raman spectrum – acollection of peaks at certain photon frequencies – that is unique to each molecule and can be used as a fingerprint for identification purposes. This methodology makes it not only possible to tell which molecules are present, but also in what amounts. Quantifying the amount of a certain substance from a Raman spectrum is straightforward as there is a linear relationship between the intensity of a peak and the concentration of the corresponding molecule.

Raman process analysers are small, robust, and non-destructive, making them especially practical for in-line, and on-line, as well as at-line and offline measurements:

In-Line Measurement A probe or sampling interface is installed either inside or in-line with the process or product flow. This allows manufacturers to continuously monitor a product, performing evaluations at several different locations in parallel to determine product consistency throughout the process. It is common to put the probe inside a bioreactor to gain a more detailed insight into pivotal reactions, and to keep track of fundamental parameters such as glucose, lactate, and glutamine levels, as well as osmolality, protein aggregation, and viable cell density.

On-Line Measurement On-line measurement is similar to in-line monitoring, as samples are measured without being removed from the production line. However, a part of the product is redirected for analysis. Only a portion of the product is tested, and the diverted sample can be reintroduced into the process stream or sent to waste after analysis, depending on the application.

At-Line and Off-Line Measurement At-line and off-line measurements are very different from in-line and on-line measurements as they involve testing away from the production line. At-line measurements are still performed quite close to the production facility, whereas off-line measurements are conducted at a separate lab.

Compatible With Water Water can often be an issue when it comes to spectroscopic technologies – such as Fourier transform infra-red (FTIR) and near infra-red (NIRS) – as it has a strong absorbance in the infra-red region, which will significantly affect the results. Raman spectrometers, on the other hand, are completely unaffected by water and can be used on moist samples. In addition, they can even report on the degree of hydration, distinguishing between monohydrate, anhydrous, and trihydrate molecules.

Another key advantage that Raman spectroscopy has over other spectroscopic methods is that the generated spectrum can be evaluated automatically, and does not need to be interpreted by an expert. This makes Raman-based spectrometers very well suited to automation, and some models available on the market can even record the spectrum and give a simple ‘pass’ or ‘fail’ result, as well as generate reports, without any user intervention.

It is even possible to feed the data into an automated system that will send a notification when a target amount of a certain substance has been reached, or send a warning alarm when an issue or fault is detected. Importantly for automated protocols, Raman spectroscopy also does not require any sample preparation – unlike technologies such as FTIR.

High-end Raman spectrometers are made with the user in mind and are very easy to operate, requiring minimal validation; it is possible to build ID tests based on one sample and expand the ID library when necessary. In addition, data used for identification on one instrument can be transferred to another, saving the user from repeating work that has already been done. Set-up and validation assistance, as well as advice on how to operate the spectrometers, is available from the best Raman suppliers, and some can even help to validate chemometric models, relying on their extensive knowledge and expertise.

Continuous manufacturing can help pharma companies to make their processes more efficient and get their products to market faster while, at the same time, reducing their costs. This approach requires robust QC technology that is compatible with automation, and Raman-based spectrometers have proven to be a popular choice for this as they are easy to operate and give reliable results that are straightforward to interpret, even without expert knowledge. Raman technology is an ideal tool to use across the entire production chain, ensuring high product consistency and excellent return on investment, while simultaneously giving plenty of opportunities to gain detailed insights into the manufacturing process.