TOC Analyzer Pitfalls Part 1

TOC analyzers – or total organic carbon analyzers, or meters – were introduced in the 1960’s. Over the years, technological advancements have taken place, as many TOC analyzer manufacturers have learnt from past mistakes and made improvements to their products; however, certain performance characteristics that are necessary for proper process control have been ignored.

Two methods of oxidation are used by TOC analyzers for total organic carbon analysis: UV/Persulfate and High Temperature Combustion. The former is recommended for low level of analysis by the TOC analyzer, and the later for high levels of carbon for TOC analyzers suited for this job. Given below are some of the failure modes, failure effects and steps that need to be taken for ‘Fail-Safe’ functioning of the critical systems and subsystems of a conventional High Temperature Combustion TC (Total Carbon) / TOC analyzer and a conventional Process UV/Persulfate TOC analyzer.

Failure Modes, Effects and Remedies

Sample System

Delivery System Malfunction

Loss of sample is considered a serious problem. The sample should be measured at the sparger and at the outlet of the Reactor if you’re using UV/Persulfate systems, or after syringe or aspirated sample is delivered, in case of a high temperature combustion reactor. If the loss of sample goes undetected at the sparger, a clog in the tube at the sparger inlet would only allow the acid reagent to pass, hence a sensor placed at the outlet of the sparger, or the inlet of the reactor will be detecting the acid in place of the sample that it should detect. Some TOC analyzers avoid this pitfall by using a loss-of-sample detector at sparger.

Similarly, if loss of sample detection were not done at the reactor outlet of a UV/ persulfate TOC analyzer, a clog in the reactor or line break downstream of the TOC analyzer would remain undetected and negatively affects the results.

Reagent

Just like the loss of sample, loss of reagents is a serious problem. Loss of acid reagent will result in the inorganic carbon not been removed properly, which will interfere with the TOC analysis by providing results that show more total organic carbon than the actual amount present in the sample. If loss of persulfate reagent occurs in UV/Persulfate system, the TOC measurements will be considerably less than the actual TOC, except for ultra-pure water applications. Any leak in fitting or sample line could cause serious damage to analyzer and components. In order to avoid these pitfalls, the TOC analyzer should monitor acid and persulfate reagent consumption.