Trihalomethanes (THMs) are formed when chlorine and other disinfectants are used to clean drinking water. At certain concentrations they are considered an environmental pollutant and are carcinogenic. Public water systems are routinely monitored for THMs, and this article discusses the methods of rapidly detecting THMs in drinking water using a person-portable gas chromatograph-mass spectrometer at concentrations lower than U.S. EPA drinking water standards.
Use of portable GC-MS to detect THMs in drinking water
Four trihalomethanes (THMs)—chloroform, bromodichloromethane, dibromo-chloromethane, and bromoform—are routinely monitored in drinking water following U.S. EPA Method 524.2. This analytical method calls for on-site sample collection, sample storage at 4 °C, and transport of the sample back to a fixed-base laboratory for GC-MS analysis.
The CUSTODION™ SPME (solid phase microextraction) sampling syringe and the person-portable TRIDION™-9 gas chromatograph-toroidal ion trap mass spectrometer (GC-TMS) (Torion Technologies Inc., American Fork, UT) can be used for rapid in-field sample extraction and analysis for sample prescreening prior to sending samples to a fixed-base laboratory for confirmatory analysis. Sample extraction at the site using SPME will minimize target analyte losses when compared to traditional techniques that risk analyte loss during storage and transport. This is especially true for many highly volatile compounds. Thus, on-site chemical analysis and detection of THMs can be more timely and accurate than traditional methods of sending samples back to a fixed-base laboratory.
Field portable equipment gives investigators useful tools to guide their sampling activities. When performing environmental analysis, it is imperative that the sample is taken from the right location; the TRIDION-9 can identify where the contamination site is located by prescreening samples. Not only does this make sampling efforts more accurate, but also prevents wasted time and money in oversampling areas where there is no contamination.
When analyzing samples for any environmental chemical concern, the TRIDION-9 is an effective identification tool for volatile and semivolatile chemicals. Some environmental concerns are time sensitive whenever health and safety are at risk. With the TRIDION’s rapid analysis time, chemical threats are identified within ~3 min. Time-critical decisions can be made that might prevent harm to the public.
Because the CUSTODION sampling syringe is small and easy to use, investigators can place several syringes around a sampling site, thus collecting several samples all at the same time. This can be especially useful when testing large bodies of water. Instead of sending out several expensive analytical instruments, perhaps on separate boats, investigators can easily take with them several CUSTODION syringes for sampling. Once finished sampling, researchers can bring the syringes back to the main testing site (or boat) for analysis on the TRIDION-9. This technique is especially useful with spills or the cleanup efforts of any large bodies of water.
Experimental: Trihalomethane analysis
Figure 1 – Chromatogram of low-level detection of THMs in drinking water.
In this experiment analyzing THMs, a CUSTODION SPME syringe with a 65-µm polydimethylsiloxane /divinylbenzene (PDMS/DVB) fiber was exposed to the headspace above drinking water samples for replicate 1-min intervals following sample agitation between each sampling, for a total of 5 min sampling time. Concentrations of 10, 20, 100, and 500 ppb for each of the four THMs were tested in this manner with freshly prepared standards from a 2000-ppm stock solution.
Following each sample extraction, the SPME syringe was inserted into the TRIDION-9 GC-TMS injection port where the target analytes were desorbed into a low thermal mass injector (280 °C) coupled with a metal-clad MXT-5 capillary GC column (Restek Corp., Bellefonte, PA), 5 m × 0.1 mm, 0.4 µm df. The capillary GC was coupled to a toroidal ion trap mass spectrometer having a mass range of 45—500 m/z. An on-board user-defined compound library identified the target analytes at the sampling site.
Figure 1 shows the GC-TMS separation of trihalomethanes spiked into a drinking water sample. All four THMs were detected and positively identified by the TRIDION-9 compound library at 100 and 10 ppb.
The CUSTODION SPME syringe and TRIDION-9 GC-TMS are well-suited for field screening of water samples. The U.S. EPA drinking water standard is 80 ppb total cumulative concentration for the four THMs. At detection levels for the individual THMs of ~10 ppb, as shown here, this method can be easily used to determine compliance of drinking water samples in the field at the point source in less than 5 min. The short cycle time between injections allows the user to quickly analyze samples on-site with high sensitivity and specificity.
The authors are with Torion Technologies Inc., 796 East Utah Valley Dr., Ste. 200, American Fork, UT 84003, U.S.A.; tel.: 801-705-6600; e-mail: email@example.com. CUSTODION™ and TRIDION™ are registered trademarks of Torion Technologies Inc. CUSTODION SPME syringes are manufactured and sold under license from 1) Brigham Young University (Provo, UT) under U.S. Patent Application 11/379,716, and 2) Supelco (Bellefonte, PA) under U.S. Patent 5,691,206, and/or any divisions, continuations, or revisions thereof.