Residual Solvents in Pharmaceuticals

From ICH Guidelines to Analytical Testing

The pharmaceutical industry is subject to strict regulatory requirements to ensure the quality, safety, and efficacy of medicinal products. A key aspect of these requirements concerns residual solvents, which are used in the manufacture of active pharmaceutical ingredients (APIs), excipients, and during pharmaceutical processing.
The ICH Q3C Guideline and its European implementation, EMA/CHMP/ICH/82260/2006, are fundamental pillars of pharmaceutical quality assurance. They define clear toxicological limits for residual solvents and establish international harmonization. For pharmaceutical manufacturers, compliance with these guidelines is essential to producing medicines that are safe for patients.

The most important contents, objectives, and analytical implications of these guidelines are summarized below.

Was ist die ICH Q3C Guideline?

ICH Q3C (“Impurities: Guideline for Residual Solvents”) is a globally recognized guideline that establishes acceptable levels of residual solvents in pharmaceutical products. It defines toxicological limits and Permitted Daily Exposure (PDE) values for a wide range of solvents. According to the EMA, the guideline provides recommendations on acceptable residual solvent levels with regard to patient safety while encouraging the use of less toxic alternatives.

The key objectives of ICH Q3C are protecting patients from exposure to potentially harmful solvent residues, harmonizing international acceptance criteria, facilitating global regulatory approval processes and last but no least promoting Good Manufacturing Practice (GMP). The current European version, ICH Q3C (R9), came into effect on 29 April 2024 according to the EMA.

The EMA Guideline for the European Market

The EMA has adopted the ICH guideline as a scientific guideline for the European Union. In addition to classifying solvents, the EMA version provides further regulatory guidance, including:

• Class 1 Solvents
  Solvents that should be avoided due to their unacceptable toxicity or carcinogenic potential.
• Class 2 Solvents
  Solvents with inherent toxicity that require strict concentration limits.
• Class 3 Solvents
  Solvents with low toxicological concern and significantly less stringent limits.
• Definition of PDE values
• Guidance for pharmaceutical manufacturers and regulatory authorities

Why Is the Guideline Important for Pharmaceutical Practice?

Patient safety is the primary objective. By establishing clear toxicological limits, exposure to potentially harmful solvent residues can be minimized. Pharmaceutical manufacturers must comply with the requirements of ICH Q3C and its European implementation to obtain and maintain regulatory approval. Furthermore, these guidelines are an integral part of quality management systems and GMP compliance. They have a direct impact on manufacturing processes, product specifications, validation strategies, and batch release procedures.

Measuring Residual Solvents in the Laboratory Using Gas Chromatography

Residual solvents can originate from various stages of pharmaceutical production. Typical sources include organic synthesis processes, purification procedures, extraction processes and pharmaceutical formulation.
By far the most widely used analytical technique for demonstrating compliance with residual solvent limits is headspace gas chromatography.

Headspace Gas Chromatographie
In headspace analysis, a sample is placed in a sealed vial and heated, allowing volatile solvents to transfer into the gas phase above the sample. Only this gas phase—the “headspace”—is then injected into and analyzed by the gas chromatograph, while the non-volatile matrix components, such as APIs and excipients, remain in the vial.
Because only the gaseous phase enters the chromatographic system, the method is not only highly selective, but also minimizes stress on GC components such as the injector and column. Consequently, headspace systems require less injector maintenance than liquid injection systems.

Modern headspace instruments provide precise control of equilibration temperature and duration, ensuring a highly reproducible equilibrium distribution of analytes. As a result, headspace gas chromatography not only simplifies sample preparation but also provides highly robust and reproducible analytical results.
These advantages make HS-GC ideally suited for the determination of volatile compounds at ppm levels in pharmaceutical samples, flavor and fragrance analysis, and environmental applications.

New in HWI Lab: Agilent 8697 XL Headspace-Autosampler and Agilent 8890  Gas Chromatograph

The key advantages of the Agilent 8697 XL headspace autosampler compared with its previous model, the 7697A, are:

• Higher sample capacity
• Significantly improved self-diagnostics and predictive maintenance capabilities
• More flexible sample handling
• Lower carryover and improved reproducibility

When Does a Residual Solvent Method Need to Be Developed or Validated, and When Is Verification Sufficient?

In pharmaceutical analytics, the following principles apply:

Full method validation is required when:
•    A new analytical method is developed
•    An existing method has been significantly modified
•    The method is applied to a new matrix or product
•    The method is used as a release-relevant testing procedure under ICH or EMA requirements

In these cases, all relevant validation parameters must be demonstrated, including specificity, linearity, precision, accuracy, limit of Quantification (LOQ), robustness, etc.

Method verification is sufficient when:

• A standardized, officially recognized method (e.g., pharmacopoeial method) is adopted without modification
• The laboratory only needs to demonstrate its ability to perform the method reliably under its own operating conditions

A typical example is the implementation of a pharmacopoeial gas chromatography method for residual solvents from the European Pharmacopoeia (Ph. Eur.), United States Pharmacopeia (USP), or Japanese Pharmacopoeia (JP).

When Is a Method Performed as a Quantitative Test and When as a Limit Test?

During method validation or verification, an analytical procedure is performed as a quantitative test when the concentration of an analyte must be determined numerically. The objective is the accurate and precise measurement of a residual solvent concentration, for example to calculate the exact content of an active ingredient on a solvent-free basis.

A limit test, by contrast, is used when it is only necessary to demonstrate that a residual solvent does not exceed a specified limit or is absent. Limit tests are frequently employed for residual solvents and elemental impurities. In method validation or verification, the primary focus for limit tests is typically on specificity and limit of Detection (LOD)
For many Class 1 residual solvents, a limit test is sufficient to demonstrate compliance with regulatory requirements.

The Role of Residual Solvents in Extractables & Leachables

Packaging materials themselves may release solvents –for example, residues originating from plasticizers or adhesives. Conversely, residual solvents may facilitate the extraction of substances from packaging materials.

As a result, residual solvents can influence material compatibility, extractables and leachables (E&L) profiles and the suitability assessment of new primary packaging systems.

HWI Expertise in Residual Solvent Analysis

HWI supports pharmaceutical companies with state-of-the-art analytical technologies, comprehensive method development and validation services, and extensive regulatory expertise for the identification and quantification of residual solvents in pharmaceutical products.

We provide the analytical foundation for high-quality and safe medicines, from early-stage development to market approval. Learn more here: Laboratory Services.