Vital Components of TOC Analyzers’ Analytical Methods
Total organic carbon (TOC) analysis by TOC analyzers may be divided into three stages—acidification, oxidation and detection and quantification. Out of all the components, accurate detection and quantification are considered the most vital. Here, we take a look at two methods used for detection in TOC analysis.
TOC Analyzers’ Common Methods of Detection
In modern TOC analyzers used for total organic carbon analysis, conductivity and non-dispersive infrared (NDIR) detection are the two most widely employed detection methods.
Conductivity
Conductivity detectors used by modern TOC analyzers are of two types: direct and membrane. Direct conductivity is known to be an inexpensive and uncomplicated method of measuring carbon dioxide content. There are several advantages to using a TOC analyzer, which utilizes this method, such as good oxidation of organics, no requirement of carrier gas, and good performance at the parts per billion (ppb) ranges. But, direct conductivity has a very limited analytical range.
The use of membrane conductivity in TOC analyzers is similar to direct conductivity as far as the technology used in both is concerned. Although it’s more robust than direct, the time required for analysis by the TOC analyzer slows down the process. Sample conductivity is analyzed before and after oxidization in both methods. The difference between the measurements is related to the total organic carbon present in the sample.
Non-dispersive infrared (NDIR) Method
The NDIR method is the only practical interference-free method by a TOC analyzer for carbon dioxide detection in total organic carbon analysis. The best use of NDIR is in the direct and specific measurement of carbon dioxide generated by oxidation of the organic carbon in the reactor.
NDIR TOC Analyzer Technology—Static Pressurized Concentration (SPC)
SPC is a new TOC analyzer NDIR technology. In this method, exit valve of the detector is closed so that the detector becomes pressurized. An analysis of the carbon dioxide is performed, once the gases in the detector have reach equilibrium state. This process of pressurizing the sample gas stream in the NDIR improves sensitivity and precision because it measures all of the oxidation products present in a sample at once, unlike flow-through cell technology.
The signal given out is proportional to the carbon dioxide concentration in the carrier gas, from the oxidation of the sample aliquot. Total organic carbon analysis method that combines UV/ Persulfate oxidation with NDIR detection has multiple benefits, such as relatively fast sample analysis time. TOC analyzers using this method has multiple applications including purified water (PW), water for injection (WFI), etc.