Many industries, including pharmaceuticals and water quality, often measure a sample’s total organic carbon (TOC). These instruments come in various forms, including some that use combustion, others that rely on ultraviolet persulfate oxidation, and so on. Some TOC analyzers also combine approaches to oxidation. According to Tammy Rellar, TOC product manager at Teledyne Tekmar (Mason, OH), “Operational efficiency is paramount in today’s TOC market.”
“When looking for a TOC analyzer,” says Bob Clifford, Ph.D., TOC product manager at Shimadzu Scientific Instruments (Columbia, MD), “ask whether you want to bring the sample to the unit or the instrument to the sample. That determines whether you need a lab or an online platform.”
The type of sample also determines the best form of oxidation. Some research shows that both combustion and wetchemical methods, such as heated persulfate or UV-persulfate, work equally well on particulate samples. In general, though, some trade-off arises in the performance of different techniques. For example, combustion-based methods tend to have trouble in approaches that require low-level measurements, such as less than two parts per million of carbon.
On the other hand, a heated sodium persulfate approach can oxidize virtually all the organic compounds that are dissolved in water. The best technique really depends on the sample and the required measurement sensitivity.
Advancing the analyzers
Beyond measuring carbon, some users want even more. “People are asking for additional parameters,” says Clifford, “like TOC and total nitrogen or total phosphorous.”
No matter what an analyzer is measuring, it can read only the samples that it receives. To enhance the sampling, Shimadzu developed a Sample Thief. “This pulls the sample into the system and rinses after every sample,” Clifford explains. This provides an example of the ongoing increase in automation.
Rellar also points out that the impact of automation has changed TOC analysis. For example, the calibration and intelligent dilution of highly concentrated samples back into the calibration range— previously labor-intensive tasks—are now automated in some analyzers. “Manufacturers must meet and exceed the needs of their users,” Rellar says, “while not compromising reliability for complexity.”
In addition, modern TOC analyzers must be extremely efficient. “We sometimes forget that TOC is rather simple in terms of analysis. Technology will continue to advance TOC analysis, but it is irrelevant without reliability,” Rellar says.
Safer drinking water
When disinfecting drinking water, more utilities include TOC analysis. “We’re seeing a transition to using online TOC analyzers for this,” says Gary Engelhart, laboratory products and marketing manager at OI Analytical (College Station, TX). His colleague William Lipps, wet chemistry products manager, adds, “Previously people grabbed a sample as the water was coming in and a sample as it was going out and then analyzed the two.” He adds, “If you did that once a day, you got one difference number, but with continuous monitoring you can analyze water all day.” That technique can be used to continuously monitor how much disinfectant should be added.
Indeed, today’s TOC analyzers in general enhance simplicity but provide more data.
For additional resources on TOC Analyzers, including useful articles and a list of manufacturers, visit www.labmanager.com/toc-analyzers