Teledyne 6750 operating instructions 1:NPOC or TOC – Direct Method, 2:TOC – True Method

Theory of Operation Model 6750

To perform correct TOC analysis, the analysis system must be capable of measuring all constituents of organic carbon present in the sample: Non-Purgeable Organic Carbon (NPOC) and Purgeable Organic Carbon (POC). Correct TOC analysis must also exclude the Total Inorganic Carbon (TIC) interference.

Figure 2-1 is a basic, commonly used technique to measure the NPOC, sometimes referred to as “TOC-Direct”.

Figure 2-1: NPOC or TOC – Direct Method

In this method, acid is added to the sample, lowering its pH to approximately 2.0, at which point the carbonates present in the sample are converted to dissolved CO2. In the sparger, the carrier gas strips (sparges) the CO2 converted from the TIC and vents it, along with any purgeable (volatile) organics, leaving only NPOC in the sample. The resultant NPOC is then oxidized to CO2 in the reactor and measured by the CO2 detector as NPOC in the sample, often referred to and reported erroneously as “TOC”.

In Figure 2-2 a preferred method of performing a “TOC- True” analysis is shown.

Figure 2-2: TOC – True Method

In this case, acid is added to the sample, lowering its pH to approximately 2.0, at which point the carbonates present in the sample are converted to dissolved CO2. In the sparger, the carrier gas strips

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