| |
Description
TOC-4100
On-line TOC Analyzer
Shimadzu |
Total Organic Carbon (TOC) analysis is a well-defined and commonly used methodology that measures the carbon content of dissolved and particulate organic matter present in water. Many water utilities monitor TOC to determine raw water quality or to evaluate the effectiveness of processes designed to remove organic carbon. Some wastewater utilities also employ TOC analysis to monitor the efficiency of the treatment process. In addition to these uses for TOC monitoring, measuring changes in TOC concentrations can be an effective "surrogate" for detecting contamination from organic compounds (e.g. petrochemicals, solvents, pesticides). Thus, while TOC analysis does not give specific information about the nature of the threat, identifying changes in TOC can be a good indicator of potential threats to a system. Attributes and Features TOC analysis consists of inorganic carbon removal, oxidation of the organic carbon into CO2, and quantification of the CO2. The primary differences between different on-line TOC analyzers are in the methods used for oxidation and CO2 quantification.
The oxidation step can be high or low temperature. The determination of the appropriate analytical method (and thus the appropriate analyzer) is based on the expected characteristics of the wastewater sample (TOC concentrations and the individual components making up the TOC fraction). In general, high temperature (combustion) analyzers achieve more complete oxidation of the carbon fraction than do low temperature (wet chemistry/UV) analyzers. This can be important both in distinguishing different fractions of the organics in a sample and in achieving a precise measurement of the organic content of the sample.
Three different methods are also available for detection and quantification of carbon dioxide produced in the oxidation step of a TOC analyzer. These are:
- Nondispersive infrared (NDIR) detector
-
Colorimetric methods
-
Aqueous conductivity methods
The most common detector that on-line TOC analyzers use for source water and drinking water analysis is the nondispersive infrared detector.
While the differences in analytical methods employed by different TOC analyzers may be important in compliance or process monitoring, high levels of precision and the ability to distinguish specific organic fractions from a sample may not be required for detection of a potential chemical threat. Instead, gross deviations from normal TOC concentrations may be the best indication of a chemical threat to the system (see below).
STIP-toc High Temperature
On-line TOC Analyzer
Teledyne Isco |
Sensitivity and Detection Limit The detection limit for organic carbon depends on the measurement technique used (high or low temperature) and the type of the analyzer. Because TOC concentrations are simply surrogates that can indicate potential problems in a system, gross changes in these concentrations are the best indicators of potential threats. Therefore, high-sensitivity probes may not be required for security purposes. However, the following detection limits can be expected:
- High temperature method (between 680?C and 950?C or higher in a few special cases, best possible oxidation): = 1 mg/L carbon
-
Low temperature method (below 100?C, limited oxidation potential): = 0.2 mg/L carbon
Response Time The response time of a TOC analyzer may vary depending on the manufacturer's specifications, but it usually takes from 5 to 15 minutes to get a stable, accurate reading. Maintenance On-line TOC analyzers are designed to operate in remote locations without continuous surveillance by an operator. However, to operate reliably, the instruments require regular calibration, inspection, and maintenance by technically skilled personnel. Previous research recommends that, at a minimum, a weekly check should be done if the analyzer is in a remote location. Table 1 provides a list of available TOC analyzers and summarizes their important attributes. Table 1: Comparison of Total Organic Carbon Analyzers | Product | Sensitivity/ Detection Limit | Reliability/ Ruggedness | Response Time | | HACH / 1950plus On-line TOC Analyzer | 0.015 mg/L for range of 0-5mg/L | High | 8 min | | Teledyne Isco / STIP-toc High-Temperature TOC Analyzer | 2 mg/L | High | 3-15 min | | Teledyne Isco / EZ TOC II Low-Temperature TOC Analyzer | 1.5% for 0-75% full scale; 2.5% for 75-100% full scale | High | 8 min | | Teledyne Isco / STIP-scan Analyzer | 1 mg/L | High | 1-10 min | | Shimadzu TOC-4100 | Variable. Settings from 0-5 ppm to 0-1,000 PPM | High | 4 min | | Teledyne Tekmar Phoenix 8000 UV-Persulfate TOC Analyzer | 2 ppb - 10,000 PPM | High | 1-3 min | | Teledyne Tekmar Apollo 9000/9000 HS Combustion TOC Analyzer | 100 ppb- 25,000 PPM and 4 ppb- 4,000 PPM | High | 1-3 min |
Cost On-line TOC analyzers range from $18,000 - $28,000. Vendors
Disclaimer: The information provided in this guide does not constitute an endorsement by the Environmental Protection Agency of any non-Federal entity, its products or its services. In addition, EPA does not endorse the vendors and products listed on this site. EPA is publishing lists of vendors on this site in an effort to further public awareness of vendors identified as possible contacts for further information and possible purchase of the different types of security equipment. The Agency has selected the listed vendors on that basis. The list of vendors is not a complete list, and EPA does not endorse the products or services of these vendors. Hach Company / GLI International / Hydrolab
P.O. Box 389
Loveland, Colorado 80539
(800) 227-4224
www.hach.com
| Teledyne Isco
4700 Superior St.
PO Box 82531
Lincoln, Nebraska 68504
(800) 228-4373
www.isco.com
| Teledyne Instruments-Tekmar
4736 Socialville Foster Rd.
Mason, Ohio 45040
(800) 874-2004
www.teledynetekmar.com
| Shimadzu America/Shimadzu Scientific Instruments, Inc.
7102 Riverwood Dr.
Columbia, Maryland 21046
(800) 477-1227
www.ssi.shimadzu.com
| Ionics Instrument Business Group
6060 Spine Road
Boulder, Colorado 80301
(304) 444-9543
www.ionicsinstruments.com
|
|
