Total organic carbon (TOC) analyzers are a mainstay in industries that must detect and quantify carbon content from many samples and sources. Unlike spectroscopy, which measures specific carbon species from their unique interactions with light, TOC analysis doesn’t tell which specific carbon-containing species are present. Nevertheless, it does provide information on impurities, which is invaluable in evaluating environmental samples. TOC analysis is mandatory for many labs, particularly in semiconductors for process water; or in regulated industries that work with ultrapure water for processing, instrumentation, cleaning/ cleaning validation, or human drugs. Other industries that regularly employ TOC analysis include pharmaceuticals, foods, forensics, oil and gas, and the life sciences.
TOC analysis involves sample acidification and oxidation down to CO2, followed by detection and quantification. Acidification is used to remove inorganic carbon; oxidation occurs either through direct, high-temperature (1300°C) or catalytic (680°C) combustion, or through a technique involving either ultraviolet radiation or thermal oxidation in the presence of persulfate.
The detector is the heart of TOC analyzers. Two main techniques are used to quantify carbon dioxide: conductivity and non-dispersive infrared (NDIR). Conductivity is a straightforward measurement involving either direct measurement or membranebased analysis. Direct conductivity has a limited analysis range but is inexpensive, doesn’t require carrier gas, and is sensitive to parts-perbillion (ppb) levels. Membrane-based conductivity is somewhat more complicated and takes longer, but is more robust and provides a greater analysis dynamic range.
NDIR should be considered the detection method of choice because it is interference- free and directly measures TOC generated during the oxidation step. Static pressurized concentration (SPC) provides improved sensitivity and precision by concentrating the oxidized sample and measuring it all at once instead of through a flow cell.
One emerging trend in TOC is the analysis of solids. Jeff Lane, a TOC specialist at OI Analytical (College State, TX), says his company is working on a new solids module that captures CO2 in a sampling bag that collects oxidized material from replicate samples. “Solids work because samples are not always as homogeneous as liquids or suspensions,” says Mr. Lane. “A collector bag helps overcome heterogeneity.”
Once the gas is collected, it can feed into a cavity ring spectrometer or even a mass spectrometer, which provides both TOC values and 12C13C isotope ratios, which are useful in determining the geographic origins of carbon-containing materials. Environmentalists have considered using isotope ratios from feathers or droppings to map bird migration, forensic food scientists use it to pinpoint the origins of high-value products such as olive oil, and pharmaceutical companies employ isotopes to detect counterfeits.
As it catches on, TOC analysis on solids could replace approved, legacy test methods that were developed years ago for materials not normally thought of as carbonbearing, such as concrete. This will take time, Mr. Lane says, because “only a certain number of people are willing to overcome inertia.”
Customers considering the purchase of a TOC analyzer, and particularly wondering whether to acquire a combustion or persulfate oxidation model, should consider potential down time and ongoing direct costs together.
Multi N/C 3100
- Suitable for all samples
- Includes Focus Radiation NDIR-Detector and VITA® Flow Management System
- Catalytic high-temperature oxidation up to 950°C
- High sensitivity down to the lowest ppb range
Sievers 5310 C
- Designed specifically for municipal drinking water applications
- Offers 12-month calibration stability and complies with USEPA-approved methodology
- Features automated protocols such as TOC percent removal calculation
- Suitable for raw and finished drinking water monitoring for DBP compliance
GE Analytical Instruments
Model 9210p and Model 9210e On-Line
- Provide analysts with a reliable tool for Online TOC monitoring
- Includes analyzers built around wet chemical (Model 9210p), electrochemical (Model 9210e), and UV oxidation
- Configured for ease of use and to reduce utility requirements
- Features a wide sample range from 4 μg/L to 30,000 mg/L
- Uses a proprietary 680°C combustion catalytic oxidation method to analyze all organic compounds
- Features automatic sample acidification and sparging, as well as automatic dilution
- High-precision mass flow controllers ensure uninterrupted carrier gas