Currently, liquid chromatograph–ultraviolet spectrometry (LC–UV) is typically applied to cleaning validations because of its familiarity, robustness, ease of use, and regulatory acceptability. For low-dose compounds, equipment requiring low residue limits, and compounds lacking strong chromophores, the enhanced sensitivity and selectivity of liquid chromatography–mass spectrometry–mass spectrometry (LC–MS–MS) facilitates rapid method development for the detection of low levels of residues of active pharmaceutical ingredients (APIs). LC–MS–MS is an acceptable technique for the analysis of API residues for cleaning validation. More importantly, in applications where sensitivity and selectivity are inadequate using traditional modes of detection, LC–MS–MS offers substantial advantages. LC–MS–MS will afford faster development and analysis time, potentially making it the predominant tool of choice.

To ensure safe pharmaceutical drug products, international guidance for manufacturing (e.g., the International Conference on Harmonization [ICH] or current good manufacturing practices [CGMP]) requires that levels of impurities in drug products be carefully monitored and controlled (1). In addition to impurities explicitly addressed by the ICH guidance, pharmaceutical products may be contaminated by process-related impurities, residues of cleaning agents, lubricants, and airborne matter such as dust and particulates. These products may also be tainted by cross-contamination from previously manufactured products. To minimize this manufacturing process carryover, methods for cleaning manufacturing equipment are put in place. These cleaning methods, which depend on the physical and chemical properties of the API and excipients, typically involve high-pressure spraying of a series of surfactant and solvent solutions. The cleaning methods are validated or verified to ensure cleanliness for each specific API by swabbing predefined areas of the manufacturing equipment that have product contact or collecting equipment rinses. The swabs or rinse solutions are then analyzed for API content and evaluated against an established residue limit. Residue limits are set with consideration of the therapeutic dose of the previously manufactured API, toxicity concerns, equipment surface areas, subsequent batch sizes, and dosing regimens of subsequent products (2, 3). Although each individual situation requires a thorough assessment, a carryover equivalent to 0.1% of the lowest daily therapeutic dose in the highest daily dose of subsequently prepared products is generally acceptable (2).

Analytical methods to support residue determinations for cleaning verification are an essential part of good manufacturing processes. These methods can be either nonselective (e.g., total organic carbon [4] and gravimetric analysis [5]) or compound-specific. For compound-specific assays, high-performance liquid chromatography–ultraviolet spectrometry (HPLC–UV) is most commonly used for the separation and detection of drug residues (6, 7, 8, 9). Nonetheless, determinations by gas chromatography (GC) (10), thin-layer chromatography (TLC) (11), ion-mobility spectroscopy (12) and enzyme-linked immunosorbent assay (ELISA) (13) also have been reported in the literature. For low-dosage drugs, whose development is increasingly common (14), or compounds with poor UV chromophores, the required residue limits can present significant analytical challenges. In addition, dosage-form manufacturing equipment is now available that makes use of very small batch sizes (gram scale) (15). This smaller batch size can lead to residue limits that are significantly lower (10–100-fold) than those calculated using more typical manufacturing equipment because the batch size is a multiplier in the residue limit calculation (2,3), and the available swabbing area is considerably smaller than typical manufacturing equipment. This article explores the use of LC–MS to achieve the sensitivity and selectivity necessary for the determination of low-level drug residues in performing cleaning verification analyses.