USP-NF Stimuli Article on Analysis of Residual Solvents

In the Pharmacopeial Forum, 51(2), a Stimuli Article entitled "Direct Analysis of Class 2 Residual Solvents Using Molecular Rotational Resonance Spectroscopy" has been published.

Residual Solvent Analysis

Residual solvent analysis is essential for ensuring pharmaceutical product quality and regulatory compliance. USP Chapter <467> Residual Solvents is the USP documentary standard for the control of residual solvents in pharmaceutical products. Traditional methods such as static headspace gas chromatography (SH-GC) have limitations, particularly in detecting low-volatility solvents.

The study by Alexander V. Mikhonin, Reilly E. Sonstrom, Justin L. Neill, and Edmond Biba presented in the Stimuli Article explores the potential of Molecular Rotational Resonance (MRR) spectroscopy for residual solvent analysis. It presents the development and validation of a continuous headspace-MRR method for the analysis of selected Class 2 residual solvents.

Overview of MRR Spectroscopy

MRR spectroscopy utilizes microwave radiation to analyze the rotational spectra of molecules, providing a high level of selectivity. Unlike chromatographic techniques, MRR spectroscopy can directly analyze complex mixtures without prior separation, potentially improving efficiency and accuracy in residual solvent analysis.

Study Findings

The study focuses on the development and validation of a continuous headspace-MRR method for analyzing selected Class 2 residual solvents.

MRR spectroscopy is proposed as a complementary method to SH-GC, particularly for low-volatility solvents such as dimethyl sulfoxide (DMSO), water-soluble acids, and volatile amines. The technique enables direct analysis of residual solvent mixtures and provides detailed spectral data for both identification and quantification.

The results suggest that MRR spectroscopy meets the ICH and USP requirements for most Class 2 and Class 3 solvents, and can also detect a subset of Class 1 solvents. Furthermore, its online compatibility allows for real-time monitoring, supporting pharmaceutical manufacturing processes such as process analytical technology (PAT) and quality by design (QbD).

The full article is available on PF Online via the USP Website Access Point. The deadline for submitting comments is 31 May 2025.