Time to switch to TOC?

In applications where detecting the overall absence of contaminants becomes more important than determining the actual compounds present, TOC can prove to be a more cost-effective, sensitive and rapid method than more specific analytical techniques. Moreover TOC can deal with unanticipated compounds. One area in which it is gaining growing use is for cleaning validation testing in the pharmaceutical/biotech industries.

Specific versus non-specific Which analytical techniques are best for monitoring system cleanliness? Techniques broadly fall into two primary categories: specific and non-specific. In cleaning validation the most commonly-used specific method, i.e. one that detects a unique compound in the presence of potential contaminants, is High Performance Liquid Chromatography (HPLC). The most common non-specific method is Total Organic Carbon (TOC), where 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 many individual assays to be performed, with the potential to overlook and therefore miss detecting some cleaning agents or unanticipated contamination. 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. 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/Persulphate oxidation such as the Sievers 800 TOC analyser1, which uses membrane conductometric detection techniques. Such analysers have been shown to offer advantages over HPLC in the areas outlined below.

Current regulatory uses TOC analysis is already being used for regulatory purposes in the pharmaceutical industry2-6. The US Pharmacopoeia (USP), Japanese Pharmacopoeia (JP) and European Pharmacopoeia (EP) prescribe its use in various stages of pharmaceutical manufacture, such as WFI (Water for Injectables). 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 only be modified slightly to accommodate cleaning validation, and one cleaning validation protocol can serve at multiple locations throughout a facility.

Comparison studies TOC provides excellent sensitivity and product recovery. Multiple comparison studies have been performed to determine the effectiveness of TOC versus HPLC for cleaning validation applications. In one such study by Jenkins et al7, of all the analytical methods tested (among those, TOC and HPLC analysis), TOC analysis was the preferred method. Citing good recoveries in all cases for a number of compounds, TOC 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 to other methods, and can detect all carbon-based residuals." As stated, TOC yields high sample recovery. Additionally, this is true even of those compounds that are generally thought to be insoluble in water. 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; see Table A8. Also, TOC, as a non-specific method, can detect all carbon-containing components of the sample. Its increased sensitivity, as low as 0.05 ppb for some instruments enables users to detect contamination not possible via HPLC. With TOC the user knows that the contamination of all of the reactive and non-reactive compounds used in the manufacturing process will have been reduced to an acceptable level, including detergents and contamination generated from unknown or unanticipated sources. Although there is literature to suggest that surfactant analyses via HPLC is possible, often these analyses are performed on concentrated products. This results in high detection limits and limits of quantification, which may or may not allow for the detection of the products in the dilute form in which they are likely to be found in cleaning validation samples. Again, as TOC is a non-specific method, it can detect all carbon-containing components of the detergent, and its increased sensitivity allows for detection of contamination not possible via HPLC. Additionally, the time-sensitivity associated with biotechnology products that degrade quickly is a concern for the labour and time-extensive HPLC tests. 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 specifically identify the contaminant since the worst-case assumption was made9.

Rapid analysis 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 appropriate software, more than two dozen 40ml samples can be prepared and analysed sequentially, without an operator present. Coupled with faster analysis time for TOC, typically six minutes, greater sample throughput is achieved relative to HPLC while encouraging unattended operation of the analyser.

Lower cost TOC has a lower capital cost and cost of ownership. In general, the capital cost of a TOC analyser is significantly lower than that of an HPLC, up to 25%. 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 entirely. Additionally, operating costs for TOC analysis is a fraction of the cost, from 40 to 75% of that of a traditional HPLC. This does not account for 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. Also to be considered is the ease of routine TOC analysis. It requires no special training and requires minimal method development, freeing the operator for other tasks. HPLC operation often requires specially-trained, higher-paid personnel, and unattended sample analysis is not possible. TOC analysis for cleaning validation is becoming a more valuable, more frequently-used tool7. 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. A library of technical/academic papers on TOC and other techniques for the medical, semiconductor and pharmaceutical industries is provided on Ionics Instruments' website www.ionicsinstruments.com