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Minimizing Your Instrument Background for Total Organic Carbon Analysis
Industry: Environmental
Instrument: Apollo 9000 Total Organic Carbon (TOC) Analyzer, Phoenix 8000 Total Organic Carbon (TOC) Analyzer
The design of this study is to present a description of common challenges experienced with the instrument blank for Total Organic Carbon (TOC) analysis using the most commonly used oxidation techniques of UV/Persulfate and High Temperature Combustion (HTC).
Consideration of detection limits is important for low-level Total Organic Carbon (TOC) measurements. An instrument detection limit not only establishes how low a Total Organic Carbon (TOC) sample can be quantified, it is also an indirect indicator of the ease at which low level TOC samples can be measured with good accuracy and precision.
Detection limits are determined by the ratio of sample TOC response to Total Organic Carbon (TOC) background for a given TOC instrument. Instrument background, often referred to as the instrument blank, can be broken down into elements that are common to almost all Total Organic Carbon (TOC) instrument and elements that are specific to a particular oxidation technology. General background elements include: the rinse water used to clean sample pathways between samples, the Total Organic Carbon (TOC) derived from the surface encountered in the sample pathway either from the material itself which is often Teflon based or though permeation of that material by CO2 in the atmosphere, and any Total Organic Carbon (TOC) contribution from the acid that is used in the removal of inorganic carbon interferences
Persulfate analyzers have additional TOC background from the persulfate used in the oxidation process. This element can be reduced for low level Total Organic Carbon (TOC) analysis by cutting the amount of reagents used in the process. For UV based instruments, the persulfate can be reduced significantly for low-level TOC measurements.
HTC analyzers have additional TOC background from the catalyst used and from sample residue buildup in the combustion furnace. Standard Method 5310 states: “The high-temperature methods accumulate nonvolatile residues in the analyzer, whereas, in Method C (The Persulfate-Ultraviolet or Heated-Persulfate Oxidation Method), residuals are drained from the analyzer. Method C (The Persulfate-Ultraviolet or Heated-Persulfate Oxidation Method) generally provides better sensitivity for lower-level (<1mg/L) samples.” This accumulating effect on the blank for the HTC method of detection can result in a shifting blank. While UV/persulfate provides consistent blanks and low-level standard response in comparison to HTC. While UV/persulfate provides consistent blanks and low-level standard response in comparison to HTC.
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