Yuefeng Xie, Postdoctoral Research Associate
Denise C. Springborg, Research AssistantDavid A. Reckhow, Associate Professor
Part of this paper was presented at AWWA WQTC, Miami, Florida: November 8, 1993
Revised: June 30, 1994
A liquid-liquid solvent microextraction-acidic methanol methylation method was developed for the analyses of haloacetic acids and ketoacids in drinking water by gas chromatography-electron capture detector. The method detection limits were determined to be 0.2 µg/L for dichloroacetic acid, 0.09 µg/L for trichloroacetic acid, 0.4 µg/L for monobromoacetic acid and 0.07 µg/L for dibromoacetic acid. The spike recoveries were 115% for monochloroacetic acid, 111% for dichloroacetic acid, 109% for trichloroacetic acid, 118% for monobromoacetic acid and 108% for dibromoacetic acid. Comparing these method detection limits and recoveries with those reported in the Standard Method showed both methods to be comparable except that for monochloroacetic acid. The statistical study indicates that there is no difference between the HAA concentration with diazomethane methylation and that with acidic methanol methylation. For glyoxylic acid and pyruvic acid analyses, both diazomethane and acidic methanol methylation gave comparable results. More study is needed to improve the methylation efficiency of monochloroacetic acid and ketomalonic acid.
Since dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were first reported in chlorinated drinking water in the 1980s (1), a number of studies have shown these compounds to be ubiquitous and of human health concern (2-5). Accordingly, the US Environmental Protection Agency (USEPA) is considering five major haloacetic acids (HAAs) for regulation in the disinfectants and disinfection by-products (D-DBP) rule (6). The maximum contamination level (MCL) is likely to be 60 µg/L for the total concentration of the five HAAs; monochloroacetic acid (MCAA), DCAA, TCAA, monobromoacetic acid (MBAA) and dibromoacetic acid (DBAA). Bromochloroacetic acid (BCAA) and these five HAAs are likely to be included for regulation in the forthcoming information collection rule (ICR) (7). The USEPA is also considering the regulation of the other HAAs; bromodichloroacetic acid (BDCAA), chlorodibromoacetic acid (CDBAA) and tribromoacetic acid (TBAA) in the coming phase II D-DBP rule as well.
A number of studies have been reported on the qualitative or quantitative analyses of HAAs (8-11). Two analytical methods for HAAs, USEPA 552 and Standard Method 6233, are currently being used to analyze HAAs in drinking water (12-13). Diazomethane derivatization is used to convert haloacetic acids to their esters in both methods. Diazomethane is prepared on site with a potent carcinogen, 1-methyl-3-nitro-1-nitrosoguanidine (MNNG)(14). Due to the toxicity of MNNG, a great concern has been expressed over its use in HAA analysis especially in water utility laboratories. A liquid-solid extraction and acidic methanol derivatization technique has been reported recently as USEPA Method 552.1 for HAA analysis (15). This acidic methanol derivatization procedure precludes the need for diazomethane. However, very few laboratories are using this method due to the unfamiliar liquid-solid extraction. The ketoacids; glyoxylic acid, pyruvic acid and ketomalonic acid, have been recently reported in ozonated waters (16-18). Although little is known about the human health effects of ketoacids, they are of interest because of their ability as a chemical surrogate for assimilable organic carbon (AOC) (19-20). An O- (2,3,4,5,6-pentaflorobenzyl)-hydroxylamine (PFBHA) and diazomethane double derivatization procedure has been published for ketoacids (16-18).
The objectives of the present study are (1) to develop a microextraction and acidic methanol derivatization procedure for HAA analysis, (2) to develop a PFBHA and acidic methanol procedure for ketoacid analysis, (3) to determine the method detection limits and recoveries of HAA analysis, and (4) to test these methods with laboratory spiked samples and field samples.
Pilot Plants and Sample Handling. Two sources of HAA field samples were used in the present study. One set of samples were obtained from a pilot plant, located at the Lake Gaillard water treatment plant, New Heaven, CT. This pilot plant is owned and operated by the South Central Connecticut Regional Water Authority (SCCRWA). The pilot plant treats typical a New England surface water (e.g. low DOC, low turbidity and low alkalinity). The treatment train consists of rapid mix, ozonation, and filtration with different media (sand, anthracite and GAC). The water samples were chlorinated at a dose of 20 mg/L at pH 7 and kept at 20°C for 72 hours in the Environmental Engineering Laboratory of the University of Massachusetts at Amherst for the HAA formation potential (FP) study. Another set of samples were obtained from a pilot plant owned and operated by the Passaic Valley Water Commission (PVWC). The raw water for this plant has high DOC and low level of bromide. The treatment train consists of rapid mix, chlorination or preozonation, and filtration with different media (sand, anthracite and GAC). The water samples were chlorinated at a dose of 1-5 mg/L for 72 hours for the simulated distribution system (SDS) testing.
HAA Analysis. For both sets of analyses, as shown in Figure 1 , 30 mL of sample was quenched with sulfite and supplemented with sodium sulfate to facilitate extraction of the acids. Each was then extracted with 4 mL of MTBE (with 300 µg/L of dibromopropane as an internal standard) for 15 minutes with a mechanical shaker. For the acidic methanol derivatization, 1 mL of extract was transferred to a 20 mL vial containing 2 mL of methanol and 0.1 mL of concentrated sulfuric acid. The vials were capped with PTFE faced septa and screw caps, then kept in a 50°C water bath for 1 hour. After adding 5 mL of 10% sodium sulfate solution and 1 mL of fresh MTBE, the vials were recapped and shaken for 2 minutes by hand. After settling, 1 mL of MTBE extract was transferred to a 2 mL autosampler vial and submitted for GC analysis. For the diazomethane derivatization, 1 mL of extract was dosed with 0.25 mL of diazomethane according to Standard Method 6233 (13). After quenching the residual diazomethane, the extracts were ready for GC analysis. The GC analysis was performed on a Hewlett-Packed gas chromatograph with an electron capture detector (13).
For routine analysis of HAAs, 30 mL of a quenched and salted aqueous sample was extracted with 3 mL of MTBE (with 300 µg/L of dibromopropane) for 15 minutes with a mechanical shaker and followed by the acidic methanol derivatization.
Seven replicates of a 1 µg/L HAA aqueous standard were analyzed to determine the MDL for each HAA. The MDL is equal to 3.14 times of the standard deviation (13). Analyte recovery was determined by analyzing a treated water sample that was previously spiked with different levels of HAAs. The mean recovery is equal to the slope of the plot of measured concentration versus the spiked concentration.
Ketoacid Analysis. The unquenched field samples were derivatized within four hours of collection according to the following procedure, as shown in Figure 2 . To a 40 mL vial containing 1 mL of 6 mg/L aqueous PFBHA stock (Aldrich Chemical), 20 mL of water sample was added. After incubation at 45°C for 1 hour and 45 minutes, the sample was cooled to room temperature. Following addition of 1 mL of concentrated sulfuric acid, the sample were shaken by hand with 4 mL of MTBE (with 3 mg/L of dibromopropane) for 3 minutes. For acidic methanol methylation, about 1 mL of extract was transferred to a 20 mL vial containing 2 mL of methanol and 0.1 mL of concentrated sulfuric acid. The vials were capped with PTFE faced septa and screw caps, then kept in a 50°C water bath for 1 hour. After adding 5 mL of 10% sodium sulfate solution and 1 mL of fresh MTBE, the vials were recapped and shaken for 2 minutes by hand. After settling, 1 mL of the MTBE extract was transferred to a 2 mL autosampler vial and submitted for GC analysis. For diazomethane derivatization, 1 mL of extract was kept in a -10°C freezer for 7 minutes. After adding 0.25 mL of diazomethane, the extract was transferred to a 4°C refrigerator for 15 minutes and then left at room temperature for 15 minutes. After quenching the residual diazomethane with silica gel, the extracts are ready for GC analysis (18).
HAA Analysis. By analyzing seven HAA samples at the level of 1 µg/L the MDLs were determined to be 0.2 µg/L for DCAA, 0.09 µg/L for TCAA, 0.4 µg/L for MBAA and 0.07 µg/L for DBAA. No MDL for MCAA was obtained due to the absence of the MCAA peak. The spike recoveries were 115% for MCAA, 111% for DCAA, 109% for TCAA, 118% for MBAA and 108% for DBAA. Comparing these MDLs and recoveries with those reported in the Standard Method showed both methods to be comparable except the MDL of MCAA. The absence of MCAA peak at low levels indicates that acidic methanol has a low methylation efficiency for MCAA. The poor methylation efficiency of MCAA was also found by other researchers (21).
A typical gas chromatogram of an HAA field sample methylated with acidic methanol is shown in Figure 3 (top). Comparing the gas chromatogram of the same sample methylated with diazomethane ( Figure 3 , bottom), one finds that acidic methanol methylation gives a better baseline and fewer interfering peaks. DCAA concentrations with two methylation procedures are compared in Figure 4 . If both methods give identical results, the data points will fall on the 45° line. If acidic methanol methylation gives higher DCAA concentration, the points will fall above the 45° line. If acidic methanol gives lower DCAA concentration, the points will fall below the 45° line. In Figure 4 , all 21 DCAA data points are distributed near the 45° line. It indicates that both methylation procedures give similar DCAA results. Similar TCAA results are shown in Figure 5 . For samples with a concentration of 50 µg/L or higher, TCAA data were not obtained with the diazomethane method due to the presence of an interfering peak. Therefore, only 17 TCAA data points were shown in Figure 5 . The acidic methanol methylation method may be less susceptible to certain types of chromatograph interferences.
Further statistical study was carried out to evaluate the difference of HAA results between diazomethane methylation and acidic methanol methylation. The t-test was used for this purpose (22). By calculation, the value of the test statistic, t0, is 0.831 for DCAA. For the t distribution (alpha = 0.05) the critical value of t0.05, 20 is 1.725. For TCAA the t0 is -0.640 and the t0.05, 16 is 1.740. Since for both DCAA and TCAA the critical value of t is greater than the absolute of the test statistic value; | t0 |, there is no significant difference between the HAA results methylated with diazomethane and that with acidic methanol.
Due to the low methylation efficiency for MCAA, more study is needed to improve its methylation efficiency for the acidic methanol procedure. As reported previously, derivatization temperature and time are two critical factors which affect HAA (22)
Round Robin Testing for HAAs. In 1993, Camp Dresser & McKee Inc. conducted a seven laboratory round robin testing for trihalomethane and haloacetic acids. A set of six identical drinking water samples were analyzed at seven separate laboratories. These samples included chlorinated, chloraminated, blank and spiked samples. The micro-extraction acidic methanol methylation was employed by the University of Massachusetts (UMass). The EPA 552 or Standard Method 6233 was employed by other six laboratories. The method report limits for UMass and other six laboratories are shown in Table 1 .
The HAA results are shown in Table II . Although the HAA concentrations reported by seven laboratories varied, the HAA results from UMass are in the range of HAA results reported by six other laboratories. Some of results from six laboratories indicate various analytical problems (e.g. extremely high MCAA concentration, extremely low HAA concentration or low HAA spike recovery). For sample 6, some of the HAA concentrations from UMass are higher than the results of six laboratories . However, since sample 6 is prepared by spiking 15 µg/L of each HAA into sample 4, the results from UMass are closer to the concentration which was expected. These round robin testing results indicate that the micro-extraction and acidic methanol extraction method is equivalent to US EPA 552 or Standard Method 6233 and less problematic.
Ketoacid Analysis. Similar studies were conducted for ketoacids. The comparison of two ketoacids; glyoxylic acid and pyruvic acid, as determined by two derivatization procedures are shown in Figure 6 and Figure 7 . All twelve data are distributed closely around the 45° line. This indicates that both diazomethane and acidic methanol derivatization give comparable results. Due to the poor response of its derivative with acidic methanol, no ketomalonic acid results was obtained. More study is need to optimize the methylation efficiency for ketomalonic acid with acidic methanol.
The authors thank the US National Science Foundation and Dr. Edward H. Bryan for their financial support of this research under grant number BCS-8958392 and the South Central Connecticut Regional Water Authority and the Passaic Valley Water Commission for providing financial support and access to the pilot plants. Thanks also go to graduate research assistant Jonathan M. Weiner for his technical assistance.
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