Cleaning validation - the rise of TOC

Penny Bristol, of Ionics Instruments, considers some advantages of TOC over specific analyses for cleaning validation

In the next few years Total Organic Carbon (TOC) prescribed by both the USP and EP for Water for Injectables (WFI) could overtake specific analytical techniques for cleaning validation tests in the pharmaceutical and biotech industries. With cleaning validation, detecting the overall absence of contaminants could be more important than determining the actual compounds present. Here, TOC is more cost-effective, sensitive and rapid. Moreover, it can deal with unanticipated compounds.

So, which analytical techniques are best for monitoring system cleanliness? They fall into two primary categories:

• Specific. A specific method is a method which detects a unique compound in the presence of potential contaminants. Each compound within a given sample will be evaluated by an assay specific to that compound. The most commonly used specific method in cleaning validation is High Performance Liquid Chromatography (HPLC);

• Non-specific. The most common non-specific method is TOC. A non-specific method is one that detects any compound that produces a certain response. In the case of TOC, all organic or carbon-containing species, regardless of the classification of these species, will be detected by a single total organic carbon analysis.

Often in cleaning validation applications, it is necessary to establish limits based upon more than one target residue. TOC, as a non-specific assay, can detect a variety of residues in a single test. HPLC, a specific assay, dictates that only one anticipated residue could be detected for a given test. In a cleaning application with multiple compounds of interest, including active ingredients, excipents and cleaning agents, a specific method would require individual assays to be performed, with potential for some cleaning agents or unanticipated contamination to remain undetected.

TOC analysis allows for all of these ingredients to be detected, and in a single analytical test that will detect the carbon concentration contributed by all ingredients.

current regulations

Methods of analysis for TOC analysers vary, some are better than others for TOC determination in cleaning validation applications. For purposes here all key features, data and attributes are in reference to TOC models that use UV/persulfate oxidation coupled with the membrane conductometric detection technique, such as the Ionics Model 820 TOC analyser.¹ Such analysers have been shown to offer advantages over HPLC.

TOC analysis is already being used for regulatory purposes in the pharmaceutical industry.^2,3,4 The US Pharmacopoeia (USP) Chapter 643 prescribes TOC monitoring of water used for all stages of pharmaceutical manufacturing, including WFI and purified water (PW). The European Pharmacopoeia (EP) Chapter 2.2.44 requires a mandatory use of TOC for WFI and allows either TOC or Oxidisable substances testing for PW in bulk. The Japanese Pharmacopoeia (JP) dictates that WFI when produced by ultra filtration is monitored by TOC.

Due to these regulatory requirements, most facilities will have a TOC analyser in-house already. The additional expense of providing an alternative means of analysis for cleaning validation need not be incurred. Additionally, protocols developed for regulatory purposes need be modified only slightly to accommodate cleaning validation, and one cleaning validation protocol can serve at multiple locations throughout a facility.

TOC effectiveness

TOC provides greater sensitivity and excellent product recovery. Multiple comparison studies have been performed to determine the effectiveness of TOC versus HPLC for cleaning validation applications. In one such study,⁵ of all the analytical methods tested TOC analysis was the preferred method. Citing good recoveries in all cases for a number of compounds, the test consistently performed as well as, or better than, HPLC.

A strong argument was made for the use of TOC analysis in cleaning validation: 'TOC has low-level detection, rapid analysis time, is low cost as compared with other methods, and can detect all carbon-based residuals.'

As stated, TOC yields high sample recovery. This is true for a multitude of compounds across a range of classifications, table 1. Studies have been carried out to show that TOC methods can also be applied to carbon-containing compounds that have limited water solubility, and recovery results are equal to, or better than, those achieved by HPLC, table 2⁶.

unanticipated compounds

Also, as a non-specific method, TOC can detect all carbon containing components of the sample. Its sensitivity - as low as 0.05 ppb for some instruments, such as the Sievers 800 TOC Analyser - enables users to detect contamination not possible via HPLC, for example, it can detect detergents, unanticipated contamination and degradable products not evaluated by HPLC. With TOC the user knows that the contamination of all of the reactive and non-reactive compounds used in the manufacturing process has been reduced to an acceptable level, including detergents and contamination generated from unknown or unanticipated sources.

Although there is literature to suggest that surfactant analysis via HPLC is possible, often these analyses are performed on concentrated products, resulting in high detection limits and limits of quantification. These high detection limits may or may not allow for the detection of the products in the dilute form in which they are likely to be found in validation samples.

Additionally, the time-sensitivity associated with biotechnology products that degrade quickly is a concern for the labour and time-intensive HPLC tests. The ease of sample preparation, the short analysis time and the non-specificity of TOC make it ideal for analysis of those active materials that degrade quickly, such as biotechnology products that degrade as a result of the cleaning.

As TOC evaluates all of the carbon contributing compounds for a given sample, from a contamination standpoint it provides the worst-case scenario. One cleaning validation strategy is to assume that all residues detected are due to the most potent or toxic potential contaminant, typically the active ingredient. When determining the carbon concentration, the worst-case assumption is used and all carbon is attributed to the most toxic material.

If this determination yields results that are less than the previously established limits, then it should not be necessary to identify the contaminant specifically since the worst-case assumption was made.⁷

TOC encourages high sample throughput because it is automated and has quick analysis times. Once samples have been collected and prepared, attended operation of the analyser is minimal. For example, with an autosampler and the appropriate software, more than two dozen 40cm³ samples can be prepared and analysed sequentially, without an operator being present. Coupled with the faster analysis time, typically six minutes, greater sample throughput is achieved relative to HPLC, while encouraging unattended operation of the analyser.

In general, the capital cost of a TOC analyser, can be 25% lower than that of an HPLC. As mentioned above, most facilities will have a TOC analyser in place for USP purposes. The same analyser can serve both USP and cleaning validation purposes, potentially eliminating the need for a capital purchase.

Additionally, operating costs for TOC analysis are only 40-75% of that for a traditional HPLC. This does not take into account the additional time required of HPLC for frequent maintenance and calibration; calibration of some TOC analysers need only be performed annually and routine maintenance is minimal.

growing use

Also to be considered is the ease of performing routine TOC analysis. It needs no special training and requires minimal method development. The operator is often free for other tasks, while HPLC operation often requires specially trained, higher-paid personnel, and unattended sample analysis is not a possibility.

TOC analysis for cleaning validation is becoming a more valuable, more frequently used tool. Ease-of-operation and method development, lower cost, high sensitivity and recovery, and the ability to perform automated sample analysis all serve to make TOC an ideal analytical method in cleaning validation applications.