Gatekeeper Instrumentation for Water Quality
Thermo Fisher Scientific (Waltham, MA) TOC analyzers are integrated into lab water purification systems, rather than sold as stand-alone instruments.
Within that context, TOC analyzers operate either in-line or at-line—a reference to how the sampling is done and where the analysis occurs, notes Julie Foster, product manager for water purification at Thermo Fisher Scientific.
For at-line operation, the analyzer extracts a sample periodically and runs the TOC measurement discretely and apart from the water production line. Several vendors offer similar systems. Thermo Fisher’s is incorporated into its Barnstead NanoPure brand of water purification systems, which also provides resistivity, conductivity, and temperature measurements.
A less expensive option involves in-line TOC analysis. Here, the conductivity cell exists within the purification path.
“The benefit of off-line detection is that the whole cell can be calibrated and tested independently,” Foster says. “And because it’s off line, the integrity of feedwater is less important than for in-line measurements. The feedwater can be dirtier.” Since inline TOC monitors water quality during purification, the feedwater must be cleaner.
One may ask why a TOC analyzer is needed at all in systems with UV oxidation, which practically guarantees TOC levels of less than 5 ppb.
“Customers who require accountability or traceability want to see an actual readout that they can record and keep,” Foster explains. “This includes operation under Good Laboratory Practices, which always have real-time measurements of TOC and resistivity.”
Additionally, laboratories that analyze organic materials at very low levels, say, by liquid chromatography, want assurance that compounds in their feedwater will not show up in their traces or raise the noise level. “If water is impure, the contaminants will show up in those traces,” Foster says. Additionally, critical cell culture and electrophoresis work may require documentation of acceptable TOC levels.
The U.S. Environmental Protection Agency’s Disinfectant Byproduct Rule was enacted in stages beginning in the late 1990s, as part of the Clean Water Act. The regulation holds water utilities responsible for characterizing their product for levels of disinfection byproducts (DBPs), which form when disinfectants are used to control microbial pathogens. Over 260 million Americans are exposed to DBPs.
Specifically, the rule tightens compliance monitoring requirements for trihalomethanes (THMs) and haloacetic acids (HAAs), and has been a boon for TOC monitoring, according to W. Gary Engelhart, laboratory products and marketing manager at OI Analytical (College Station, TX).
“Paralleling this, we see increased attention to online TOC, or grab-sampling, to get a better handle on levels of these contaminants in drinking water,” Engelhart tells Lab Manager. “Before this rule, online TOC measurement was an anomaly. Now people are seeking us out. It has been a tipping point.”
The HAA and THM problems are seasonal, arising mostly during warm months when algal or bacterial blooms are most likely and water companies are more inclined to use disinfectants. TOC is not the only way to quantify these compounds. OI’s own purge-and-trap system for GC-MS will do the job, and Parker Hannifin sells a dedicated THM analyzer.
Nor are HAAs and THMs the only consequence of bacterial or algal blooms. When microorganisms die, they release compounds that produce disagreeable odors, even in the ppb concentration range.
“Water plants struggle to master these situations,” Engelhart says. “TOC is a good indicator of what’s coming into the plant.”
For additional resources on TOC Analyzers, including useful articles and a list of manufacturers, visit www.labmanager.com/toc-analyzers