Introduction: Measurement, Assumptions and the Spectrum of Regulatory Risk

When auditing data required for compendial water quality testing, a passing number alone is not sufficient under GMP. FDA inspections or audits coordinated by EMA, COFEPRIS, or other regulatory agencies dig deeper, wanting to see you understand your data, not just meet minimums.

In the case of total organic carbon (TOC) and inorganic carbon (IC) measurements, the method of analysis for Ultrapure Water (UPW) and Water for Injection (WFI) release might determine whether an audit results falls into a high-risk or low-risk designation. Simply put, assumptions place you on the spectrum of regulatory risk. Only direct evidence is defensible.

What is Scrutinized in a GMP Audit?

In the case of a GMP (Good Manufacturing Practice) audit, regulators scrutinize your entire manufacturing ecosystem to verify compliance with strict quality and safety standards. Known as the "Five Pillars of GMP," an audit can target the following:

1. Procedures and Documentation: Standard Operating Procedures (SOPs), batch records, audit trails, data integrity
2. People: Employees, training records, process understanding and adherence
3. Premises: Facilities including environmental controls and maintenance, HVAC and temperature controlled storage, cleanliness and pest control
4. Processes: Evaluation of process validation to ensure the manufacturing method consistently delivers the expected results; review of change controls and deviation/CAPA (Corrective and Preventive Action) logs to see how you investigate and fix issues
5. Products: Material ingredients, final product, testing and labeling

Instrumentation for Pharmaceutical Water Quality Testing

UPW and WFI systems are guaranteed focal points of a thorough audit, and the analytical instruments that measure parameters related to water systems can expect equal levels of scrutiny. Specific to analytical instrumentation, scrutiny inevitably targets the method of measurement, as well as the data.

The technology choice for measuring TOC and the potential limitations of its carbon measurement capabilities could pose an issue under the pressure of a GMP audit, especially if it's difficult to defend results due to their lack of carbon specificity. Understanding the difference in types of carbon - organic vs inorganic - is imperative and should be taken into account long before an inspection.

Auditors evaluate laboratories by asking detailed questions about data collection methods and how results are generated and recorded. The sample questions below mirror what you're likely to hear during an audit. Take time to answer them critically. This exercise will help you assess whether your current instruments and testing methods produce the reliable, defensible batch records that auditors expect to see. If you spot weaknesses now, you can address them before an auditor does.

Demonstrating Carbon Specificity

Auditor Question 1: "How do you demonstrate carbon specificity?"

This question often creates tension during inspections, and for good reason. There is a fundamental difference between measuring actual carbon and estimating its presence through secondary signals.

Conductivity-only sensors measure the total ionic change in a sample. The problem? These sensors cannot distinguish between organic carbon and inorganic ions like chlorides or nitrates. When an inspector asks for proof of carbon specificity, a conductivity sensor offers only an assumption - that no interfering ions were present. This assumption creates a critical gap in your data trail, and assumptions don't hold up well under audit scrutiny.

Analytical instruments exist on a regulatory risk spectrum. On the high-risk end, conductivity-only sensors create significant audit vulnerabilities. When auditors question your methods or challenge your data, these sensors are difficult to defend. On the low-risk end, audit-ready carbon analyzers provide a different story. They deliver defensible, traceable data that protects your batch records and withstands regulatory scrutiny.

Instruments designed to isolate carbon in the form of CO₂ before analysis achieve an accurate TOC measurement. Physical isolation of carbon from ions prior to detection ensures specificity as a demonstrable chemical fact, not merely theory. This establishes an unbroken data trail from initial chemistry through to final electronic record. When auditors ask how you know it's carbon, you can show them, not just tell them.

Want to learn more or see data for additional challenge compounds?

Download our TOC technology guide.

Inorganic Carbon Measurement

Auditor Question 2: "How is inorganic carbon accounted for?"

Inorganic Carbon (IC) handling is a frequent target for deep-dive questioning. When FDA or COFEPRIS inspectors probe this area, they are looking for ambiguity. If your instrument infers inorganic carbon, you are forced to provide a lengthy justification that may collapse under scrutiny.

Let’s compare:

Selective, or true carbon analysis

Direct Measurement: Inorganic carbon is measured explicitly and reported independently for a clear data trail.

Audit Defense: Provides data-backed measurements that minimize the need for additional questions.

Conductivity sensor

Inferred Contribution: Inorganic carbon is assumed based on total conductivity, requiring a theoretical justification, not a data-based one.

Audit Risk: Inspector is likely to probe the validity of the assumptions, increasing audit duration and risk.

Selective carbon analysis provides a clear and simple one-sentence answer:

"We measure inorganic carbon directly via a dedicated CO₂ sensor and report it independently, eliminating the need for mathematical assumptions or theoretical water chemistry models."

Instrument of Record for Compendial Water Quality Monitoring

Auditor Question 3: "Can this be the instrument of record?"

To serve as an "Instrument of Record," an analyzer must do more than monitor trends; it must satisfy the most rigorous validation requirements (IQ/OQ/PQ) and real-time testing (RTT) ) and adhere strictly to ALCOA+ data integrity principles.

Here's a critical issue many companies overlook: some instrument manufacturers use completely different analytical technologies for online real-time testing versus lab-based sample analysis. For example, they might use a conductivity sensor for online monitoring of water loops but a combustion-based analyzer in the QC lab. When the same sample produces different results depending on which technology tested it, you face a significant problem during audits.

Veolia takes a different approach. Our Sievers systems use the same membrane-based conductivity detection technology for both online and lab-based analysis. This technology parity eliminates the analytical variability that occurs when different detection methods are applied to the same sample. Whether you're monitoring continuously in your WFI loop or validating samples in the QC lab, you're using the same analytical method.

Why does this matter? During an Out-of-Specification (OOS) investigation, technology mismatches create serious complications. If your online instrument uses different detection principles than your lab instrument, auditors will ask you to justify why the results don't align. This puts you in a complex, high-risk position where you're defending methodology differences rather than discussing actual sample quality. When both instruments use identical technology, your data tells a consistent, defensible story from your water distribution system to your QC lab.

USP <1225> Validation of Compendial Procedures

Auditor Question 4: "What is your USP <1225> specificity rationale?"

Under USP <1225>, the regulation relating to analytical procedure development and validation, the distinction between method-based specificity and justification-based specificity is paramount and could be the difference between a secure audit and a technical interrogation.

Conductivity sensors rely on justification-based specificity. Because they cannot isolate the carbon signal, they rely on the assumption that the water system is stable enough that non-carbon ions won't interfere. In a GMP environment, this theoretical, non-fact based rationale is a liability.

TOC analyzers like the Sievers M500 and Sievers M9 achieve specificity through their measurement method itself. These instruments use a gas-permeable membrane that allows only CO₂ to reach the detector while excluding interfering compounds before detection occurs. This means you don't need to justify water chemistry assumptions to an auditor. The technology has already eliminated potential interferences as part of the measurement process.

Meeting the baseline of USP <643>, UPS <1225>, and USP <1226> is expected. However, providing an experimentally demonstrable, carbon-specific signal is what provides true batch protection and audit-readiness.

Conclusion: Compliance Through Defensible Data

USP compliance is the minimum. USP defensibility is the goal.

The primary defense against audit failure is the selection of an instrument that provides specific carbon measurement and unassailable data integrity. By moving beyond the minimum requirements of USP compliance, you can provide data-backed answers, rather than narratives based on assumptions.

TOC analyzers, like the Sievers M500 and Sievers M9, satisfy the following regulatory standards for total peace of mind:

• USP <643>, <1225>, and <1226>
• FDA Alternative Method ASTM E2656-10
• 21 CFR Part 11 & EU Annex 1 Full ALCOA+ Data Integrity Standards
• Defensible for FDA, EMA, and COFEPRIS Inspections

Is your TOC method data driven and audit ready?

Download the TOC technology guide to find out.

Autores:

Fergus Keenan

Fergus is an analytical chemist turned product leader, building and commercializing scientific instruments across applications, sales, marketing, and product management. He has previously worked at various Thermo Fisher Scientific and Danaher operating companies, as well as an exciting Denver-based mass spectrometry startup named Exum Instruments.

Sidnei Jannetta

é gerente de Marketing na Veolia, com foco na linha de instrumentos analíticos Sievers. Sydney tem apoiado os clientes da Sievers nos últimos dez anos com experiência em aplicações de carbono orgânico total (COT) e endotoxinas. Ela forneceu serviços de desenvolvimento de métodos e testes de viabilidade para fabricantes farmacêuticos e apresentou em mais de 20 conferências nacionais. Sydney é bacharel em Química pela Universidade do Colorado do Norte.

Lindsey Wohlman

é especialista de Marketing na Veolia e oferece suporte à linha de instrumentos analíticos Sievers. Ela colabora estreitamente com engenheiros, cientistas e especialistas em produtos para desenvolver conteúdo que transforma informações técnicas em insights práticos para clientes B2B e partes interessadas. Sua experiência como profissional de marketing digital full-stack em tecnologia, software e manufatura lhe deu um profundo apreço pelo papel que a comunicação clara desempenha na condução da compreensão e na construção de confiança. Lindsey é bacharel pela Universidade do Colorado.