Drinking water has been, and continues to be, heavily treated for bacteria and other microscopic organisms that may cause infection in humans and other animals subsequent to consumption. In order to disinfect water supplies, halogenated materials have been introduced therein that have proven more than adequate for such a purpose. Unfortunately, although such halogenated compounds (chlorinated and chloraminated types, primarily) exhibit excellent disinfection capabilities, when present within aqueous environments at certain pH levels these halogenated compounds may generate byproducts that may themselves create health concerns. The United States Environmental Protection Agency (USEPA) in fact regulates four types of trihalomethanes (THM4) within drinking water. These THM4 are chloroform, bromoform, dibromochloromethane, and bromodichloromethane. Removal of such compounds from drinking water is not possible as for typical chlorinated and brominated disinfecting compounds, at least not at the same reliability level as for the disinfecting agents. Thus, residual amounts may remain within treated water supplies that may require further removal processing to be undertaken, or avoidance of ingestion if necessary. Of course, if the level of contamination is sufficiently low, initiation of such potentially expensive removal steps would be unwise from an economic perspective.
The USEPA currently has set a maximum contaminant level for these THM4 in drinking water of 0.080 mg/L. It is thus important to reliably analyze and measure the total amount of such contaminants in order to determine if removal if necessary.
The USEPA has instituted its own testing methods for such a purpose. For THM4, the primary test method is 502.2. The USEPA 502.2 method measures for individual and total THM4 as well as other volatile byproducts. This method utilizes a TRACOR® 540 gas chromatography with Hall/PID detectors, a Tracor LSC-2 sample concentrator, and a TEKMAR® 2050 Autosampler. Such a system is, again, very effective at measuring drinking water samples at the source, but remote analyses are not readily available as the entire system is too cumbersome to move to locations along a drinking water line. As such, on-line analysis through these protocols is difficult, expensive, and labor intensive to implement.
Measurement at the source (i.e., within a water purification plant location) may be effective for system-wide average readings; however, in the large supplies of water at such locations, the chances of proper sampling to that effect may be suspect since the contaminants may be present in varied locations, rather than definitely mixed throughout the tested water supply itself. Additionally, testing may not uncover the actual level of residual THM4 disinfection byproducts prior to the water supply being disbursed to distant dispense sites (transfer pipes, homes, schools, businesses, etc.). In any event, there is a relatively new rule in place that requires utilities to provide evidence of compliance with trihalomethane levels at multiple locations, rather than a straightforward system-wide average. There is thus a drive to implement remote testing via real-time, on-line methods for water supply THM4 contaminant level measurements.
Such a desirable on-line procedure has been difficult to achieve, however, particularly as it pertains to the determination of not only the total amount of THM4 within water supplies, but also the amount of each species of the same THM4 groups present within the tested water source. High performance liquid chromatography, utilizing electrospray ionization-mass spectrometry or ultraviolet absorbance detector, has been attempted. The sensitivity and selectivity of the high performance liquid chromatography methods are easily sacrificed without the cumbersome preparations in place, therefore requiring operator intervention during analysis. Again, this issue leads to serious drawbacks when on-line implementation is attempted.
Another methodology that has proven effective to a degree is post-column reaction-ion chromatography. This has shown promise, but only in terms of quantifying bromate ion concentrations in drinking water samples at a single microgram per liter level. This dual selectivity form (separation by ion chromatography column as well as the selective reaction with the post-column reagent with the analyte) offers an advantageous test method over the others noted above, except for the presence of more common anions, specifically chloride, at much higher concentrations within the sampled drinking water supply (mg/L instead of microgram). Separation of the THM4 species from other halogenated compounds (such as haloacetic acids), however has been problematic and caused certain degrees of interference in measuring total levels of both types of compounds within drinking water samples. Despite this problematic limitation, it was determined that fluorescence detection provided a much-improved detection protocol in comparison with ultraviolet and mass spectrometry possibilities, particularly for haloacetic acid concentrations. Thus, although such a fluorescence method of detection, coupled with the post-column reaction (again with nicotinamide reactant) and ion chromatography, exhibited the best results in terms of an on-line test method for haloacetic acid drinking water contaminant measurement levels, there remained a definite need for improvements in individual and total trihalomethane measurements and identifications within such test samples. To date, however, there has not been an analytical test protocol that has permitted implementation of such a system within an on-line real-time monitoring procedure with an acceptable degree of reliability. An automated system that provides such versatility and reliability has simply not been forthcoming within the pertinent art.