Comparative Evaluation of High-Performance Liquid Chromatography versus Total Organic Carbon Analysis for Cleaning Validation in Pharmaceutical Manufacturing: A Critical Review

Background: Cleaning validation is a critical component of pharmaceutical manufacturing quality assurance, ensuring the prevention of cross-contamination between production batches. Two predominant analytical techniques, High-Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) analysis, are widely employed for residue detection, yet the optimal selection between these methodologies remains a subject of ongoing debate within the industry.

Objective: This narrative critical review evaluates the comparative advantages, limitations, and application contexts of HPLC and TOC analysis in pharmaceutical cleaning validation programs based on published literature, providing evidence-based guidance for method selection.

Methods: A comprehensive literature-based review was conducted examining peer-reviewed publications, regulatory guidance documents, and industry case studies from 2010 to 2025. Selection criteria included studies comparing analytical performance, regulatory compliance, and practical implementation considerations. All numerical values reported, including limits of detection and analysis times, are sourced from published literature and do not represent original experimental data.

Results: Based on the reviewed literature, HPLC is generally reported to demonstrate superior specificity for Active Pharmaceutical Ingredient (API) quantification with detection limits typically ranging from 0.1-10 µg/mL, while TOC analysis is reported to offer advantages in non-specific organic contamination detection with broader applicability and faster analysis times (Typically 3-8 minutes versus 15-60 minutes for HPLC). Regulatory guidance from the FDA and EMA supports both methodologies when appropriately validated, with the selection dependent on the specific cleaning validation objectives.

Conclusions: Based on the evidence reviewed, neither technique appears to be universally superior; rather, the optimal choice depends on the validation objective, equipment characteristics, product portfolio complexity, and regulatory requirements. A risk-based approach combining both methodologies may provide the most comprehensive cleaning validation strategy for multi-product facilities.

Cleaning validation represents a fundamental pillar of Good Manufacturing Practice (GMP) compliance in pharmaceutical production, serving as the documented evidence that cleaning procedures effectively remove product residues, degradation products, cleaning agents, and microbial contamination to predetermined acceptable levels [1]. The significance of robust cleaning validation programs has been underscored by numerous regulatory observations and warning letters issued by the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA), with inadequate cleaning validation consistently ranking among the top pharmaceutical manufacturing deficiencies [2].

The pharmaceutical industry has witnessed a significant paradigm shift from traditional compliance-based approaches toward science-based, risk-based methodologies for cleaning validation [3]. This evolution reflects the application of quality risk management principles established in ICH Q9, which emphasizes scientifically justified acceptance criteria and lifecycle approaches to validation activities.

The selection of appropriate analytical methods for residue detection constitutes a critical decision in cleaning validation protocol development. High-Performance Liquid Chromatography (HPLC) and Total Organic Carbon (TOC) analysis have emerged as the two predominant techniques employed across the pharmaceutical industry, each offering distinct advantages and limitations [4]. HPLC, a specific chromatographic technique, enables the identification and quantification of individual compounds, making it particularly valuable for API residue determination [5]. Conversely, TOC analysis provides a non-specific measurement of total organic contamination, offering rapid screening capabilities and broader detection of all carbon-containing residues [6].

The debate regarding the preferential use of HPLC versus TOC in cleaning validation contexts has persisted within the pharmaceutical industry for over two decades. Proponents of HPLC emphasize its specificity and ability to correlate directly with Maximum Allowable Carryover (MAC) calculations based on API toxicity [7]. Advocates for TOC analysis highlight its rapid turnaround time, lower method development requirements, and ability to detect cleaning agent residues simultaneously with product residues [8].

Regulatory expectations have evolved to acknowledge both methodologies as acceptable when appropriately validated and scientifically justified. The FDA's guidance on cleaning validation emphasizes the importance of selecting methods with adequate sensitivity and specificity for the intended purpose [9]. Similarly, the EMA's Annex 15 revision acknowledges the utility of non-specific methods such as TOC when combined with appropriate limit justification [10].

Despite the extensive individual treatment of HPLC and TOC methodologies in the literature, there remains a notable gap in comprehensive comparative analyses that provide structured, risk-based guidance for method selection across diverse pharmaceutical manufacturing scenarios. Existing publications often address these techniques independently, with limited integration of regulatory interpretation, practical decision frameworks, and scenario-specific recommendations. Furthermore, guidance on when to employ combined approaches or tiered strategies remains fragmented across disparate sources.

This narrative critical review aims to address these gaps by providing a structured comparison of HPLC and TOC methodologies in the context of pharmaceutical cleaning validation. The unique contribution of this work lies in: (1) synthesizing published evidence on analytical performance characteristics within a unified comparative framework; (2) integrating regulatory perspectives from FDA, EMA, and PIC/S to provide interpretive guidance; (3) developing practical, risk-based decision support criteria for method selection; and (4) proposing tiered implementation strategies applicable across varied manufacturing contexts. By examining the fundamental principles, analytical performance characteristics, regulatory considerations, and practical implementation factors, this work seeks to establish a framework for informed method selection that optimizes both scientific rigor and operational efficiency.

Literature search strategy

A systematic literature review was conducted using the following electronic databases: PubMed, Science Direct, Web of Science, and Google Scholar. The search encompassed publications from January 2010 to December 2025 to capture contemporary industry practices and regulatory developments.

Search terms

The following search terms and Boolean operators were employed:

• ("cleaning validation" OR "cleaning verification") AND ("HPLC" OR "high-performance liquid chromatography")
• ("cleaning validation" OR "cleaning verification") AND ("TOC" OR "total organic carbon")
• ("pharmaceutical manufacturing") AND ("residue detection") AND ("analytical methods")
• ("cross-contamination") AND ("GMP") AND ("analytical validation")

Inclusion and exclusion criteria

• Inclusion criteria:
• Peer-reviewed original research articles, review papers, and technical reports
• Studies comparing or evaluating HPLC and/or TOC for cleaning validation applications
• Regulatory guidance documents from FDA, EMA, WHO, and PIC/S
• Industry white papers from recognized pharmaceutical associations
• Exclusion criteria:
• Non-English publications
• Non-pharmaceutical applications
• Conference abstracts without full-text availability
• Publications predating 2010 (Unless seminal works)

Data extraction and analysis

Relevant data were extracted including analytical performance parameters (Sensitivity, specificity, precision, accuracy), regulatory compliance considerations, practical implementation factors (Time, cost, training requirements), and case study outcomes. Comparative analysis was performed to synthesize findings across studies.

Literature screening summary

The initial database search yielded approximately 850 records. Following removal of duplicates (n = 215), title and abstract screening excluded 480 records not meeting inclusion criteria. Full-text review was conducted on 155 articles, of which 78 were ultimately included in this review based on relevance to comparative analytical performance, regulatory guidance, or practical implementation. Additionally, 12 regulatory guidance documents (FDA, EMA, PIC/S, ICH) and 8 industry white papers from recognized pharmaceutical associations (PDA, ISPE) were included to provide authoritative regulatory context and industry perspectives. Backward citation tracking was performed on key review articles to identify seminal works published prior to 2010 that established foundational concepts in cleaning validation methodology; five such foundational references were included. The inclusion of regulatory documents and industry white papers is justified by their authoritative role in defining compliance expectations and best practices that directly inform method selection decisions in pharmaceutical manufacturing settings.

Fundamental principles and detection mechanisms

High-Performance Liquid Chromatography (HPLC): HPLC operates on the principle of differential partitioning of analytes between a mobile phase and a stationary phase contained within a chromatographic column [11]. The technique enables separation, identification, and quantification of specific compounds based on their physicochemical properties, including polarity, molecular weight, and chemical structure.

In cleaning validation applications, HPLC methods are typically developed to target specific APIs or their degradation products. The most common detection modes include Ultraviolet-Visible (UV-Vis) spectrophotometry, fluorescence detection, and Mass Spectrometry (MS) for enhanced sensitivity and selectivity [12]. Method development requires optimization of mobile phase composition, column selection, flow rate, and detection parameters for each target analyte.

Jenkins KM, et al. [6] demonstrated that HPLC-UV methods for cleaning validation typically achieve detection limits in the range of 0.1-1.0 µg/mL for most pharmaceutical compounds, with quantitation limits of 0.5-5.0 µg/mL, depending on the chromophoric properties of the analyte.

Total Organic Carbon (TOC) analysis: TOC analysis quantifies the total concentration of carbon atoms covalently bonded in organic molecules present in a sample [13]. The technique involves oxidation of organic compounds to Carbon Dioxide (CO₂), which is subsequently measured by Non-Dispersive Infrared (NDIR) detection or conductivity measurement.

Two primary oxidation mechanisms are employed in pharmaceutical applications: High-temperature combustion (Typically 680-1000°C) and UV-persulfate oxidation [14]. High-temperature combustion offers superior oxidation efficiency for recalcitrant compounds, while UV-persulfate methods provide lower detection limits and are more suitable for samples with high inorganic carbon content.

Mirza T, et al. [15] reported that TOC analyzers utilized in pharmaceutical cleaning validation typically achieve detection limits of 0.05-0.5 mg/L (ppm) carbon, with most modern instruments providing quantitation limits suitable for cleaning validation acceptance criteria.

Comparative analytical performance

Specificity and selectivity: The reviewed literature consistently indicates that HPLC demonstrates inherent specificity, enabling the differentiation and quantification of individual compounds within complex sample matrices.

Based on published evidence, this specificity is generally reported to be particularly advantageous when:

1. Multiple APIs are manufactured on shared equipment
2. Degradation products require separate quantification
3. Regulatory requirements mandate specific API residue limits based on toxicological assessment

Walsh A, et al. [16] conducted a comparative study examining the specificity requirements for cleaning validation in a multi-product oral solid dosage facility. The authors concluded that HPLC was essential for facilities manufacturing compounds with significantly different potencies or toxicological profiles, where non-specific methods could not adequately demonstrate compliance with MAC limits.

Conversely, TOC analysis provides a cumulative measurement of all organic contamination, offering no information regarding the identity of contributing compounds. While this non-specificity is often characterized as a limitation in the literature, several authors have noted that it may offer advantages in scenarios where:

1. Detection of all organic residues (Including cleaning agents and degradation products) is desired
2. Rapid screening of equipment cleanliness is required
3. Product changeover involves chemically similar compounds with comparable toxicological profiles

Author interpretation: Based on the reviewed literature, the authors propose that specificity requirements should be determined through risk assessment rather than applied uniformly. Facilities with diverse product portfolios spanning wide potency ranges may require HPLC specificity, while those manufacturing chemically similar compounds may find TOC's non-specific detection adequate and more operationally efficient.

Sensitivity and detection limits: Comparative sensitivity between HPLC and TOC is reported in the literature to be dependent on multiple factors, including the specific analyte, sample matrix, and instrument configuration. Table 1 summarizes typical detection capabilities reported in published studies.

Note: Values represent typical ranges reported in the reviewed literature [6,15,17-19] and may vary significantly depending on instrumentation, validation strategy, compound properties, and laboratory-specific method development. HPLC-MS detection limits are compound-dependent and influenced by ionization efficiency.

Hwang RC, et al. [17] demonstrated that TOC detection limits, when converted to equivalent compound concentrations based on carbon content, may be either more or less sensitive than HPLC depending on the molecular composition of the target analyte. For compounds with high carbon content (> 50% w/w), TOC may provide superior sensitivity, while compounds with lower carbon content or strong chromophores may be more readily detected by HPLC-UV.

Author interpretation: Based on the reviewed literature, the authors propose that direct sensitivity comparisons between HPLC and TOC require compound-specific evaluation. Method selection based solely on generic detection limit comparisons may be misleading; rather, facilities should calculate equivalent detection capabilities for their specific product portfolios.

Precision and accuracy: The reviewed literature indicates that both methodologies demonstrate acceptable precision and accuracy when properly validated. Pharmaceutical regulatory requirements typically mandate Relative Standard Deviation (RSD) values of ≤ 2% for system precision and ≤ 15% for method precision at the quantitation limit [18].

A comprehensive validation study by Li X, et al. [19] compared HPLC and TOC performance for cleaning validation of pharmaceutical manufacturing equipment. The authors reported comparable precision (RSD < 5% for both methods) and accuracy (Recovery 95-105% for HPLC, 90-110% for TOC) at concentrations relevant to cleaning validation acceptance criteria.

Author interpretation: Based on the reviewed literature, the authors propose that precision and accuracy considerations alone are unlikely to be discriminating factors in method selection, as both techniques can achieve acceptable performance when properly validated according to ICH Q2(R1) guidelines.

Regulatory perspectives and compliance considerations

FDA guidance: The FDA's "Guide to Inspections Validation of Cleaning Processes" (1993) [9] acknowledges the acceptability of both specific and non-specific analytical methods, provided that appropriate scientific justification is documented. Key regulatory expectations articulated in this guidance include:

1. Methods must be validated according to ICH Q2(R1) guidelines
2. Detection limits must be adequate to quantify residues at levels below established acceptance criteria
3. Recovery studies must demonstrate the effectiveness of sampling procedures
4. Specificity requirements should be commensurate with the intended use

Based on analysis of FDA warning letters and inspection observations documented in the FDA Warning Letters Database [20], the agency has indicated acceptance of non-specific methods such as TOC when:

• The acceptance limit is based on the TOC response of the most difficult-to-detect compound
• Cleaning procedures are demonstrated to remove cleaning agents to acceptable levels
• The validation protocol includes scientific justification for method selection
• Important distinction: It should be noted that while the FDA's 1993 guidance document provides formal regulatory expectations, interpretations derived from warning letter analysis represent observed inspection trends rather than codified regulatory requirements. Facilities should consult current FDA guidance and, when appropriate, seek regulatory feedback for novel applications.

EMA and PIC/S requirements:  The European regulatory framework, as articulated in EMA Annex 15 (2015) [10] and PIC/S guidance document PI 006-3 [21], similarly supports the use of both methodologies. The EMA Annex 15 emphasizes a risk-based approach to method selection, considering:

1. Product toxicological profile and therapeutic index
2. Equipment design and cleanability
3. Cleaning procedure effectiveness
4. Sampling method recovery efficiency

The Pharmaceutical Inspection Co-operation Scheme (PIC/S) guidance PI 006-3 specifically addresses the use of non-specific methods, stating that TOC is acceptable provided that "the method can detect the marker residue or worst-case residue at a level below the acceptance criterion" [21].

Author interpretation: Based on the reviewed regulatory landscape, the authors propose that current regulatory frameworks from FDA, EMA, and PIC/S provide flexibility for method selection when supported by documented scientific rationale. However, the absence of explicit universal endorsement of either technique underscores the importance of facility-specific risk assessment and documentation of method selection justification.

Practical implementation considerations

Method development requirements: A significant practical distinction between HPLC and TOC reported in the literature lies in method development complexity. Published studies indicate that HPLC method development requires:

1. Chromatographic condition optimization (Mobile phase, column, temperature)
2. System suitability parameter establishment
3. Forced degradation studies to demonstrate stability-indicating capability
4. Matrix effect evaluation for each equipment type and product combination

TOC methods, by contrast, are reported to require minimal compound-specific development. A single validated TOC method can theoretically serve all organic compounds, with method validation focusing on:

1. Instrument calibration and linearity verification
2. System suitability using standard solutions
3. Recovery studies for specific equipment and sampling procedures

Westman L, et al. [22] estimated that TOC method implementation requires significantly less time for the development effort compared to HPLC, representing significant resource savings for multi-product facilities.

Throughput and turnaround time

The literature consistently reports that TOC analysis provides substantially faster results compared to HPLC, with typical analysis times of 3-8 minutes versus 15-60 minutes for chromatographic methods [23]. This difference becomes particularly significant in high-throughput manufacturing environments where:

1. Rapid equipment release is critical for production scheduling
2. Multiple sample points require analysis per cleaning event
3. Real-time decision-making regarding re-cleaning is necessary

The faster turnaround time of TOC has led to its adoption for routine cleaning verification in many facilities, with HPLC reserved for periodic validation studies or specific applications requiring compound identification [24].

Cost considerations: Economic evaluation of HPLC versus TOC must consider both capital investment and operational costs. Table 2 provides a comparative cost analysis based on industry survey data and vendor quotations reported in the literature.

Application-specific recommendations

Scenarios favoring HPLC: Based on the evidence reviewed, the literature generally indicates that HPLC may be the preferred methodology in the following scenarios:

• High-Potency API (HPAPI) manufacturing: The enhanced specificity and sensitivity of HPLC (Particularly HPLC-MS) is reported to be essential for demonstrating compliance with extremely low acceptance criteria (ng/cm² range) typical of HPAPI cleaning validation [25].
• Toxicological limit-based approaches: When MAC calculations are based on compound-specific toxicological data (Permitted Daily Exposure, PDE), specific quantification of the residual API is generally required to demonstrate compliance.
• Degradation product monitoring: Facilities requiring separate quantification of API and degradation products must employ chromatographic methods capable of compound differentiation.
• Regulatory requirements mandating specific detection: Certain products or markets may have explicit regulatory requirements for specific analytical methods.

Scenarios favoring TOC

Based on the evidence reviewed, the literature generally indicates that TOC analysis may be the preferred methodology in the following scenarios:

• Multi-product facilities with diverse portfolios: The non-specific nature of TOC eliminates the need for compound-specific method development, providing substantial efficiency gains for facilities manufacturing numerous products [26].
• Cleaning agent residue detection: TOC effectively detects organic cleaning agents (Surfactants, solvents) that may not be readily detectable by HPLC methods developed for API quantification.
• Rapid turnaround requirements: Facilities requiring rapid equipment release benefit from the shorter analysis times of TOC.
• Visual cleanliness correlation: When cleaning procedures result in visually clean equipment and TOC provides confirmation of overall organic contamination removal.

Risks associated with inappropriate method selection

• Author interpretation: Based on the reviewed literature, the authors emphasize that inappropriate method selection carries significant risks that warrant careful consideration:
• Risk of exclusive TOC reliance: In scenarios involving high-potency compounds or products with significant toxicological differences, exclusive reliance on TOC may provide false assurance of cleanliness. Because TOC measures total organic carbon non-specifically, a passing TOC result could mask the presence of a highly potent API residue if the acceptance limit was established based on a less potent compound's carbon response. For example, if equipment previously used for a cytotoxic compound is cleaned and evaluated using TOC with limits derived from a non-cytotoxic product, subtherapeutic but toxicologically significant residues could remain undetected, potentially resulting in serious patient harm and regulatory non-compliance [25].
• Risk of exclusive HPLC reliance: Conversely, exclusive reliance on HPLC may be inefficient and potentially provide incomplete assurance in facilities with diverse product portfolios or where cleaning agent residue detection is critical. An HPLC method developed specifically for API detection would not detect organic cleaning agent residues (Surfactants, detergents) unless separately validated for such purposes. This could result in cleaning agent carryover that, while not representing API contamination, may affect subsequent product quality or stability. Furthermore, in high-throughput environments, the extended analysis time of HPLC may create operational bottlenecks, incentivizing inadequate sample evaluation or premature equipment release [8, 22].
• These considerations underscore the importance of risk-based method selection aligned with specific product characteristics, facility operations, and intended cleaning validation objectives.

Combined approach strategies: Many industry practitioners advocate for a combined approach utilizing both methodologies in a complementary manner. Liu and Hwang [8] proposed a tiered strategy wherein:

• Tier 1 (Routine Verification): TOC analysis for rapid, non-specific screening of all cleaning events
• Tier 2 (Periodic Validation): HPLC analysis at defined intervals to confirm specific API removal
• Tier 3 (Investigation): HPLC deployment for out-of-specification investigations or process changes

This risk-based approach optimizes resource utilization while maintaining scientific rigor and regulatory compliance.

This narrative critical review of published literature on HPLC and TOC methodologies for pharmaceutical cleaning validation demonstrates that neither technique possesses universal superiority. Rather, optimal method selection requires careful consideration of multiple factors within a risk-based framework.

Risk-based decision framework: The evidence reviewed supports a decision logic wherein method selection is driven by:

• Product risk profile: High-potency compounds or those with established toxicological limits (PDE-based) generally warrant HPLC specificity, while standard-potency products with similar toxicological profiles may be adequately served by TOC.
• Regulatory defensibility: Method selection documentation should explicitly address how the chosen technique provides adequate sensitivity below acceptance criteria and appropriate specificity (or justified non-specificity) for the intended application.
• Operational context: Facilities must balance analytical rigor against operational constraints, including throughput requirements, method development resources, and equipment release timelines.
• Portfolio complexity: Multi-product facilities with diverse chemical entities may benefit from TOC's universal applicability for routine monitoring, supplemented by HPLC for specific high-risk applications.

Synthesized recommendations

The reviewed evidence supports implementation of tiered, risk-stratified analytical programs wherein TOC serves as an efficient screening tool for routine cleaning verification, while HPLC is strategically deployed for initial validation, periodic confirmation, investigation of excursions, and applications involving high-potency or toxicologically distinct compounds. This combined approach maximizes both regulatory defensibility and operational efficiency.

Facilities should document their method selection rationale within cleaning validation protocols, explicitly addressing how chosen methods align with product-specific risk assessments, regulatory expectations, and operational requirements. Ongoing evaluation through trend analysis ensures continued method suitability as product portfolios and regulatory expectations evolve.

Recommendations for implementation

Based on the findings of this review, the following recommendations are provided for pharmaceutical facilities implementing or optimizing cleaning validation analytical programs:

• Conduct a comprehensive risk assessment considering product portfolio, equipment characteristics, and operational requirements before selecting primary analytical methodology.
• Establish acceptance criteria using a scientifically justified approach (toxicological, dose-based, or general limit) and ensure selected analytical methods possess adequate sensitivity.
• Validate all analytical methods according to ICH Q2(R1) guidelines, with particular attention to recovery studies using production-representative sampling procedures.
• Consider a tiered approach utilizing TOC for routine verification and HPLC for periodic confirmation or specific applications requiring compound identification.
• Document the scientific rationale for method selection in cleaning validation protocols to support regulatory inspections.
• Maintain ongoing evaluation of analytical program effectiveness through trend analysis and periodic reassessment of method suitability [27-30].

Future perspectives

Emerging analytical technologies may provide additional options for cleaning validation in the future. Technologies under development or early adoption include:

• Direct surface analysis: Techniques such as DART-MS (Direct Analysis in Real Time Mass Spectrometry) enable direct surface interrogation without swab extraction [28].
• Spectroscopic methods: Near-Infrared (NIR) and Raman spectroscopy offer potential for rapid, non-destructive surface analysis.
• Electrochemical sensors: Development of compound-specific sensors may enable real-time, in-situ monitoring of cleaning effectiveness.
• Machine learning integration: Application of artificial intelligence to spectroscopic data may enhance both specificity and throughput of non-destructive methods.

These emerging technologies warrant continued investigation and may eventually supplement or replace traditional HPLC and TOC methodologies.

The authors declare no conflict of interest.

1. Guide to inspections of validation of cleaning processes. Office of Regulatory Affairs, FDA. Food and Drug Administration. 1993.
2. Bismuth G, Neumann S. Cleaning validation: A practical approach. CRC Press; 2000. doi: 10.1201/9780367801212.
3. Vaghela U. Risk-based cleaning validation in pharmaceutical manufacturing: A comprehensive review. International Journal of Multidisciplinary Research and Growth Evaluation. 2025;6(6):1067-1073. doi: 10.54660/.IJMRGE.2025.6.6.1067-1073.
4. LeBlanc DA. Cleaning validation: Practical compliance solutions for pharmaceutical manufacturing. Pharmaceutical Technology. 2020;44(7):32-38.
5. Snyder LR, Kirkland JJ, Dolan JW. Introduction to modern liquid chromatography. 3rd ed. John Wiley & Sons; 2011. doi: 10.1002/9780470508183.
6. Jenkins KM, Vanderwielen AJ, Armstrong JA, Leonard LM, Murphy GP, Piros NA. Application of total organic carbon analysis to cleaning validation. PDA Journal of Pharmaceutical Science and Technology. 1996;50(1):6-15.
7. Fourman GL, Mullen MV. Determining cleaning validation acceptance limits for pharmaceutical manufacturing operations. Pharmaceutical Technology. 1993;17(4):54-60.
8. Liu C, Hwang RC. Total organic carbon as a universal method for cleaning validation. Pharmaceutical Engineering. 2009;29(4):1-8.
9. Guide to inspections validation of cleaning processes (7/93). Office of Regulatory Affairs, FDA. Food and Drug Administration. 1993. 
10. Qualification and validation. European Commission Health and Consumers Directorate-General. European Commission. 2015.
11. Meyer VR. Practical high-performance liquid chromatography. 5th ed. John Wiley & Sons; 2010. doi: 10.1002/9780470688427
12. Jin SE, Ban E, Kim YB, Kim CK. Development of HPLC method for the determination of levosulpiride in human plasma. J Pharm Biomed Anal. 2004 Jun 29;35(4):929-36. doi: 10.1016/j.jpba.2004.02.024. PMID: 15193738.
13. Clesceri LS, Greenberg AE, Eaton AD. Standard methods for the examination of water and wastewater. 20th ed. American Public Health Association; 1998.
14. Total Organic Carbon (TOC) analysis: Principles and applications. Technical Bulletin. Shimadzu Corporation. 2020
15. Mirza T, Lunn MJ, Keeley FJ, George RC, Bodenmiller JR. Cleaning level acceptance criteria and a high pressure liquid chromatography procedure for the assay of Meclizine Hydrochloride residue in swabs collected from pharmaceutical manufacturing equipment surfaces. J Pharm Biomed Anal. 1999 Apr;19(5):747-56. doi: 10.1016/s0731-7085(98)00299-4. PMID: 10698538.
16. Walsh A, Mayer P, Schultz T. Practical considerations for cleaning validation in multi-product facilities. Journal of GXP Compliance. 2013;17(4):64-72.
17. Hwang RC, Lin Y, Horwitz W. Statistical approaches for establishing cleaning validation acceptance criteria and assessing cleaning performance. Journal of Validation Technology. 2013;19(2):1-12.
18. ICH Q2(R1): Validation of analytical procedures: Text and methodology. ICH Harmonised Tripartite Guideline. International Council for Harmonisation. 2005.
19. Li X, Ahmad IAH, Tam J, Wang Y, Dao G, Blasko A. Cleaning verification: A five parameter study of a Total Organic Carbon method development and validation for the cleaning assessment of residual detergents in manufacturing equipment. J Pharm Biomed Anal. 2018 Feb 5;149:33-39. doi: 10.1016/j.jpba.2017.10.021. Epub 2017 Oct 26. PMID: 29100028.
20. Warning letters database. FDA Office of Regulatory Affairs. Food and Drug Administration. 2021.
21. PI 006-3: Recommendations on validation master plan, installation and operational qualification, non-sterile process validation, cleaning validation. PIC/S Secretariat. Pharmaceutical Inspection Co-operation Scheme. 2007.
22. Ruzilawati AB, Wahab MS, Imran A, Ismail Z, Gan SH. Method development and validation of repaglinide in human plasma by HPLC and its application in pharmacokinetic studies. J Pharm Biomed Anal. 2007 Apr 11;43(5):1831-5. doi: 10.1016/j.jpba.2006.12.010. Epub 2006 Dec 16. PMID: 17240100.
23. Thomas O, Burgess C. UV-visible spectrophotometry of water and wastewater. 2nd ed. Elsevier; 2017.  doi: 10.1016/C2015-0-01629-4.
24. Hall W, Zahn M. Cleaning validation in pharmaceutical industry. In: Cleanroom technology. CRC Press; 2016. p.261-290.
25. Mohammed AM, Osman SK, Saleh KI, Samy AM. In Vitro Release of 5-Fluorouracil and Methotrexate from Different Thermosensitive Chitosan Hydrogel Systems. AAPS PharmSciTech. 2020 May 13;21(4):131. doi: 10.1208/s12249-020-01672-6. PMID: 32405869; PMCID: PMC7220897.
26. LeBlanc DA. Validated cleaning technologies for pharmaceutical manufacturing. Interpharm Press; 2000.
27. Kumar V, Rathore AS, Bharadwaj R. Cleaning validation for biopharmaceutical manufacturing: A comprehensive review. Biotechnology Progress. 2021;37(2):e3097. doi: 10.1002/btpr.3097.
28. Cody RB, Laramée JA, Durst HD. Versatile new ion source for the analysis of materials in open air under ambient conditions. Anal Chem. 2005 Apr 15;77(8):2297-302. doi: 10.1021/ac050162j. PMID: 15828760.
29. Valavala S, Seelam N, Tondepu S, Sundaramurthy V. Cleaning Method Validation for Estimation of Dipyridamole Residue on the Surface of Drug Product Manufacturing Equipment Using Swab Sampling and by High Performance Liquid Chromatographic Technique. Turk J Pharm Sci. 2020 Apr;17(2):182-189. doi: 10.4274/tjps.galenos.2019.70446. Epub 2020 Apr 24. PMID: 32454778; PMCID: PMC7227908.
30. Moura MJ, Pereira AD, Santos DJF, Silva AG, Paiva CCAD, Duarte BPM. Cleaning validation in pharmaceutical quality control laboratories: a structured protocol for contamination risk mitigation. Daru. 2025 Jul 3;33(2):20. doi: 10.1007/s40199-025-00566-x. PMID: 40608165; PMCID: PMC12229404.