ACIDIC METHANOL methylation for HAA ANALYSIS: LIMITATIONS AND POSSIBLE SOLUTIONS

ACIDIC METHANOL methylation for HAA ANALYSIS: LIMITATIONS AND POSSIBLE SOLUTIONSAuthor(s): YUEFENG XIE, INNI RASHID, HAOJIANG ("JOE") ZHOU and LESLIE GAMMIESource: Journal (American Water Works Association), Vol. 94, No. 11 (November 2002), pp.115-122Published by: American Water Works AssociationStable URL: http://www.jstor.org/stable/41298394 .

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Acidic methanol methylation is a common derivatization process for haloacetic acid (HAA)

analysis. The Pennsylvania State University at Harrisburg and EPCOR Water Services in

Edmonton, Alta., conducted a study on acidic methanol methylation for HAAs. Using the

current methylation conditions (US Environmental Protection Agency method 552.2), the

authors observed incomplete methylation of HAAs, especially for trihaloacetic acids, which

could significantly affect the accuracy of these HAA analytical results. The effects of

methylation time, methylation temperature, volume of acidic methanol, and composition of

acidic methanol on methylation efficiency were studied. This research suggests that acidic

methanol methylation efficiency could be improved by increasing the volume of acidic

methanol, methylation temperature, methylation time, or all three. The authors also

investigated other common analytical problems associated with acidic methanol methylation.

Additional studies are suggested to further optimize the acidic methanol methylation

procedure for HAA analysis.

ACIDIC METHANOL

in ethylati

o n0 haa analysis:

LIMITATIONS

AND POSSIBLE SOLUTIONS

BY YUEFENG XIE,

INNI RASHID,

HAOJIANG ("JOE") ZHOU,

AND LESLIE GAMMIE

Haloacetic

tion tection

matter by-products

and

Agency

acids chlorine

(HAAs),

(USEPA, (DBPs)

(Reckhow formed

1998) that are

under

& by

regulated Singer, the

the

reaction

promulgated

1990), by the

between are US

a Environmental Disinfectants/DBP

group natural

of disinfec- organic

Pro- matter and chlorine (Reckhow & Singer, 1990), are a group of disinfec-

Haloacetic

tion by-products (DBPs) that are regulated by the US Environmental Pro- tection Agency (USEPA, 1998) under the promulgated Disinfectants/DBP Rule (D/DBPR). The maximum contaminant level for five HAAs is 60 jig/L.

A number of analytical methods for HAAs have been developed (Xie, 2000; Barth & Fair, 1992). Under the D/DBPR, however, only three analytical methods - USEPA method 552.1 (USEPA, 1992), USEPA method 552.2 (USEPA, 1995), and standard method 625 IB (Standard Methods , 1998) - are approved for HAAs in drinking water because of their sensitivity, reliability, and relative simplicity. When these three methods are used, it is necessary to convert the free acid form of HAAs to their methyl esters, which can be relatively easily separated by gas chromatography (GC) columns.

For many years, diazomethane was the preferred methylation reagent because of its good methylation efficiency. However, typically diazomethane is freshly generated with a chemical - l-methyl-3-nitro-l-nitrosoguanidine (MNNG) - which is a potent carcinogen. Because of the toxicity of MNNG and the hazardous nature of diazomethane, many laboratories, especially water utility laboratories, are reluctant to adopt this method.

XIEETAL | PEER-REVIEWED | 94:11 • JOURNAL AWWA | NOVEMBER 2002 1 15



FIGURE 1 Effect of methylation time on methylation of six haloacetic acids (conducted at The Pennsylvania State University at Harrisburg)

♦- CIAA o CI2AA - CI3AA - v- BrCI2AA

CIBr2AA - a - Br, 3 A A 2.0-i 3

o £ 1.5- (0 £ .~a

8 1-0- M • • f. ° ....... - O - O O Q. /• M • O

• f. ° "S y o „ * E 0.5- ' E 0.5- o

L ^ 0.0-

1 1 1 1 1 1 0 40 80 120 160 200

Methylation Time - min CIAA - monochloroacetic acid, CI2AA - dichloroacetic acid, CljAA - trichloroacetic acid, BrCIAA - bromodichloroacetic acid, CI Br ^ A - chlorodibromoacetic acid, BrjAA - tribromoacetic acid

FIGURE 2 Effect of methylation time on methylation of three haloacetic acids, dalapon, and surrogate (conducted at The Pennsylvania State University at Harrisburg)

- BrAA o Dalapon - -v- BrCIAA

- v- Br2AA - Surrogate 2.0-1

o | 1.5- (0 2? 2 S 1.0- A ^ « v "O / /V ^ 0 / / y ■ 1 E 0.5- / f E 0.5- / / v o '/ o / w' •'

v ^ o

/ 0.0- n

I I I I I I 0 40 80 120 160 200

Methylation Time - min BrAA - monobromoacetic acid, dalapon- 2, 2-dichloropropionic acid, BrCIAA - bromochloroacetic acid, BrÂ - dibromoacetic acid, surrogate - 2,3-dibromopropionic acid

The author and colleagues developed a new analytical method for HAAs in drinking water (Xie et al, 1999; Xie et al, 1998) that employs liquid-liquid microextraction, acidic methanol methylation, and GC-electron capture detection (GC-ECD). Only five regulated HAAs - monochloroacetic acid (CIAA), dichloroacetic acid (CI2AA), trichloroacetic acid (CI3AA), monobromoacetic acid (BrAA), and dibromoacetic acid (Br2AA) - were included in the method. In recent years, reports on the formation of four other HAAs (Cowman & Singer, 1996; Xie et al, 1992) - bromochloroacetic acid (BrCIAA), bromodichloroacetic acid (BrCIAA), chlorodibromoacetic acid (ClBr2AA), and tribromoacetic acid (Br3AA) - have caused concern about their occurrence in drinking water. In 1995, a liquid-liquid microextraction, acidic methanol methylation, and GC- ECD procedure for all nine HAAs and 2, 2-dichloropropionic acid (dalapon) was developed and published as USEPA method 552.2 (USEPA, 1995). Since then, this method, using acidic methanol methylation, has been widely adopted for HAA analysis by many laboratories, especially those in water utilities.

Effective methylation is a critical step for HAA analysis. Poor methylation efficiency for trihaloacetic acids has been observed by a number of laboratories using diazomethane or acidic methanol. Brophy and colleagues reported poor methylation efficiency with diazomethane for three brominated trihaloacetic acids (Brophy et al, 1999). Drying the extract using anhy- drous magnesium sulfate before diazomethane methylation was proposed to improve the methylation. Brophy and co-workers also reported HAA results from three laboratories that were using diazomethane or acidic methanol (Brophy et al, 1999). Their results indicated that compared with diazomethane, acidic methanol methylation provided a better methylation efficiency for monohaloacetic acids and dihaloacetic acids but a poor efficiency for trihaloacetic acids. Incomplete methylation with acidic methanol was also reported in a study conducted by USEPA (Munch et al, 2000). Currently,

116 NOVEMBER 2002 | JOURNAL AWWA • 94:1 1 | PEER-REVIEWED | XIE ET AL



USEPA is developing an improved acidic methanol methylation method, USEPA method 552.3, for HAA analysis (Munch, 2000).

The objective of the research described here was to investigate the methylation efficiency of acidic methanol for HA As. The effects of methylation time, methylation temperature, and the volume and composition of acidic methanol were studied. Possible solutions were proposed to improve the methylation efficiency for HAAs before a new USEPA method is developed.

EXPERIMENTAL METHODS All experiments were conducted jointly by The Penn-

sylvania State University at Harrisburg, Middletown, Pa., and EPCOR Water Services in Edmonton, Alta. Experiments on the effects of methylation time, temperature, and the volume of acidic methanol were conducted in the environmental engineering laboratory at Penn State Harrisburg. Experiments on the effects of methylation time, volume of acidic methanol, and composition of acidic methanol were conducted in an EPCOR Water Services laboratory.

USEPA method 552.2 specifies the following methylation conditions (USEPA, 1995). The acidic methanol solution is 10% sulfuric acid (H2S04) in methanol by volume. The ratio between the volume of the methyl tertiary butyl ether (MTBE) extract and the volume of the acidic methanol is 3:1. The derivatization temperature is 50°C, and derivatization time is 2 h. In order to more accurately evaluate the method's methylation efficiency and effects of other methylation conditions, the methylation conditions specified in method 552.2 were used without modification. For each set of tests, a method 552.2 methylation comparison run was conducted. When a specific methylation condition was studied, only that condition was changed within a range that bracketed the condition specified in method 552.2.

At Penn State Harrisburg, GC1 coupled with a mass selective detector (MSD)2 was used to study the effect of methylation time on methylation efficiency. A newly developed GC-MSD procedure (Xie, 2001) was used for the study. HAA commercial standards were directly prepared in MTBE solvent without preparing and extracting aqueous samples. A GC with ECD3 was used to study the effects of temperature and the volume of acidic methanol. Aqueous samples were prepared, salted, acidified, and extracted with MTBE solvent. For all studies at Penn State Harrisburg, an internal standard (1,2-dibromopropane) was used. After methylation, 1 mL of fresh MTBE (without the internal standard) was added to the acidic methanol mixture, and the mixture was back-extracted with 4 mL of 10% sodium sulfate (Na2S04) solution. The extract was then submitted to GC analyses.

At EPCOR Water Services, a GC with ECD4 was used for all experiments. All samples were made by spiking

At Pennsylvania State University in Harrisburg, a gas chromatograph with an electron capture detector was used to study the effects of temperature and acidic methanol volume on haloacetic acid methylation.

reagent water with certified commercial standards. These samples were acidified, salted, and extracted with MTBE. After methylation, the acidic methanol mixture was neu- tralized and back-extracted with sodium bicarbonate (NaHC03) solution. The MTBE extract was then submitted for GC analysis. In some of the studies, duplicate runs were performed, and precision was <20%. When the effect of acidic methanol volume was studied, the final MTBE extract was adjusted to 3 mL with fresh MTBE. This adjustment was made because increasing the volume of acidic methanol increased the solubility of MTBE in water and decreased the final volume of MTBE extract. The volume adjustment was necessary, especially because an internal standard was not used. Other sample preparation and analysis procedures were similar to that in method 552.2 (USEPA, 1995).

Because of incomplete methylation of some HAAs and variable HAA concentrations in samples used in the study, all results were normalized against the results obtained with the methylation condition under method 552.2. When method 552.2 methylation conditions were used, the normalized peak areas have a value of 1, regardless of the methylation efficiency, sample preparation procedure, or HAA concentrations. Normalized peak areas were cal- culated by dividing the peak areas resulting from the new experimental conditions by the peak areas obtained using method 552.2 methylation conditions. When an internal standard was used, the results were expressed as normalized peak area ratios.

To minimize the uncertainty of the results, multiple testing conditions were used. For instance, 10 time inter- vals were used for the methylation time study at Penn State Harrisburg. The multiple testing conditions provided the information on the methylation efficiency and sensitivity of each methylation condition. Two studies, including methylation time and acidic methanol volume,

XIEETAL | PEER-REVIEWED | 94:11 • JOURNAL AWWA | NOVEMBER 2002 117



FIGURE 3 Effect of methylation time on methylation of six haloacetic acids (conducted at EPCOR Water Services)

♦ CIAA o CI2AA - CI3AA - v- BrCI2AA

CIBr2AA - q - BroAA 2-°i

3 p

//■ //

/y v 1.5- - , -T (0 0)

< a 1-0- •••■«- -i

8 / 0 *-"r I0-5- /

0

I 0

0.0- 6^

- I 1 1 1 1 1 0 40 80 120 160 200

Methylation Time - min CIAA - monochloroacetic acid, CI2AA - dichloroacetic acid, Ci3AA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CIBrÂ - chlorodibromoacetic acid, Br3AA-tribromoacetic acid

FIGURE 4 Effect of methylation temperature on methylation of six haloacetic acids (conducted at The Pennsylvania State University at Harrisburg)

CIAA 0 CI2AA - CI3AA - v- BrCI2AA - »- CIBr2AA - d Br3AA

1.6-1

-p 0 ^ ' jm £ - ̂ ̂ ̂ -v ™ 1-2- , - : T a> , • - __ - -

1 5-- - 0 T3 s ▼ - : - " == 0.8- E » I

0.4- D'

1 1 1 45 50 55

Methylation Temperature - °C

CIAA- monochloroacetic acid, CIÂ - dichloroacetic acid, CI3AA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CI Br ^ A - chlorodibromoacetic acid, BrjAA - tribromoacetic acid

were also duplicated in two laboratories - Penn State Harrisburg and EPCOR Water Services. More important, the methylation conditions were evaluated under various sample preparation and analysis conditions (e.g., with or without an internal standard, ECD or MSD, and NaHC03 or Na2S04 for neutralization and/or extraction). These variations significantly reduced both random and systematic errors of the study.

RESULTS AND DISCUSSION Incomplete methylation with acidic

methanol. Methylation of HAA with acidic methanol was studied at both Penn State Harrisburg and EPCOR Water Services. The methylation conditions described under USEPA method 552.2 were used to analyze the samples with various methylation times (Figures 1-3). The normalized peak area (ratio) for 120 min specified in method 552.2 was 1. A normalized value < 1 indicates a poorer methylation efficiency compared with that at 120 min, a method 552.2 condition. A normalized value > 1 indicates that a better methylation efficiency was obtained.

Results from Penn State Harrisburg are shown in Figures 1 and 2. The methylation time zero refers to those samples that were extracted and ana- lyzed right before they were put in the 50°C water bath. These samples were left at room temperature for ~ 5-10 min during sample preparation. For CIAA and BrAA, significant amounts of acids (-60%) were methylated at room temperature. For these two monohaloacetic acids, a complete methylation was achieved after 15-min incubation at 50°C. For three dihaloacetic acids -

C12AA, BrClAA, and Br2AA - methylation rates were much slower than those for monohaloacetic acids. Nevertheless, for all three dihaloacetic acids, a complete methylation was achieved after 2 h at 50°C, which was specified under USEPA method 552.2. However, for four trihaloacetic acids - CI3AA, BrCl2AA, ClBr2AA, and Br3AA - the methylation was incomplete after 2 h. With one additional hour, or 180 min total, a 14% increase in normalized




peak area ratio was observed for CI3AA and 28% for Br3AA. Because methylation curves for all four trihaloacetic acids were not plateaued, methylation efficiency could be further increased by increasing the methylation time. Using 2-h methylation at 50°C, incomplete methylation was also observed for dalapon and the surrogate, 2,3-dibromopropionic acid, as shown in Figure 2.

Similar results were obtained at EPCOR Water Services (Figure 3). For C1AA and C12AA, a complete methylation was achieved before or at 2 h at 50°C. For four trihaloacetic acids, however, only partial methylation was achieved at 2 h of methylation at 5 0°C. Significant percentages of trihaloacetic acids were methylated after 2 h. For Br3AA, normalized peak area was increased ~ 95% after 190 min of methylation. This indicates that the maximum methylation efficiency using 2-h methylation could be < 50%. Results for BrAA, BrClAA, and Br2AA were also obtained and were comparable to those obtained at Penn State Harrisburg.

The results from both laboratories indicated that mono- and dihaloacetic acids achieved a complete methylation under the conditions specified in method 552.2. However, a complete methylation was not achieved for four trihaloacetic acids, dalapon, and the surrogate. These results were in agreement with those obtained in a study conducted by USEPA (Munch et al, 2000). Although comparable results for mono- and dihaloacetic acids were obtained in both laboratories, differ- ent methylation efficiencies were observed for four trihaloacetic acids. The difference between the methylation results from Penn State Harrisburg and EPCOR Water Services could be attributable to minor variations in their methylation conditions, i.e., methylation temperatures, volume ratios between the MTBE extract and acidic methanol, and compositions of the acidic methanol.

The differences illustrate the impor- tance of a complete methylation. With- out a complete methylation, a minor change in the methylation conditions, e.g., time, temperature, and volume

FIGURE 5 Effect of the percentage of H2S04 in acidic methanol on methylation of six haloacetic acids (conducted at EPCOR Water Services)

- CIAA o CI2AA - -T- CI3AA - v- BrCI2AA

CIBr2AA - d - Br3AA

1'°"

/! '' ^

s °-8- 0 /'/ ' ' < '

'' J* / h ^ ' 2 / '// V ' o Q. / /, '' ' -O 0.6" ' '/ ' O S ' > '! X ' <s * i/i X ' - i' X Z 0.4- /' 'v& ^

Z# A ^

_ *

0.2- V

1 1 1 1 1 1 5 10 15 20 25 30 Percentage of H2S04 in Acidic Methanol- %

H2S04 - sulfuric acid, CIAA - monochloroacetic acid, CI2AA - dichloroacetic acid, CljAA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CIBrÂ - chlorodibromoacetic acid, BrjAA - tribromoacetic acid

FIGURE 6 Effect of the volume of acidic methanol solution on methylation of six haloacetic acids (conducted at The Pennsylvania State University at Harrisburg)

CIAA o CI2AA - CI3AA - v- BrCI2AA

CIBr2AA - q Br3AA 4-

.g "5 cc 1_ D" " d) O /

< (0 ' q! « / = 2- aj

I /' ,

1 1 1 1 1 1 1 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Equivalent Volume of Acidic Methanol Solution - mL CIAA - monochloroacetic acid, CIÂ - dichloroacetic acid, CI3AA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CI Br ^ A - chlorodibromoacetic acid, BrjAA - tribromoacetic acid




FIGURE 7 Effect of the volume of acidic methanol solution on methylation of five haloacetic acids (conducted at EPCOR Water Services)

CIAA o CI2AA - CI3AA - v- BrCI2AA

-m-- CIBr2AA 4-

(O a> < 3- <0 a! ~o a> N 75 E 2- o z

^ - v . _V" " ^ '

^

1.0 1.5 2.0 2.5 3.0 3.5 4.0 Volume of Acidic Methanol Solution - mL

CIAA - monochloroacetic acid, CIÂ - dichloroacetic acid, CljAA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CI Br ^ A - chlorodibromoacetic acid

and composition of acidic methanol, could significantly affect the methylation efficiency and analytical results. For example, the volume of the MTBE extract is com- monly measured approximately by a Pasteur pipette. This could affect the ratio between the MTBE extract and acidic methanol and result in a significant change on the HAA methylation efficiency, discussed subsequently.

Effect of methylation temperature. The effect of methylation temperature on methylation efficiency was studied at Penn State Harrisburg. Figure 4 shows the effect of temperature on the methylation efficiency of CIAA, Cl2AA, and four trihaloacetic acids. Decreasing the temperature from 50 to 45°C lowered the methylation efficiency for four trihaloacetic acids, but not for CIAA and Cl2AA. For Br3AA, decreasing the methylation temperature lowered its methylation efficiency by ~ 60%. Increasing methylation temperature from 50 to 55°C increased the methylation efficiency of all four trihaloacetic acids. A 40% increase in methylation efficiency was observed for Br3AA from 50°C to 55°C. This also indicated the incomplete methylation of four trihaloacetic acids at 50°C. For monohaloacetic acids and dihaloacetic acids, a near-complete methylation was achieved at all temperatures. There- fore, no significant effect was observed. These results were in agreement with those obtained in a USEPA study (Munch et al, 2000).

Effect of the percentage of H2S04 in acidic methanol. The effect of the percentage of H2S04 in acidic methanol was studied at EPCOR Water Services. Method 552.2 specifies a 10% H2S04 by volume for acidic methanol. This research investigated the effect of the percentage of H2S04 within a range of 5-30%. As shown in Figure 5, 10% H2S04 in methanol is the optimum formula for HAA methylation. Increas- ing or decreasing the percentage of H2S04 by 5% or more significantly lowered methylation efficiency for four trihaloacetic acids, as shown in Figure 5. For mono- and dihaloacetic acids, especially CIAA, the effect on their methylation efficiencies was less severe (Figure 5).

Effect of the volume of acidic methanol solution. The effect of the volume of acidic methanol solution on methylation efficiency was studied at both Penn State Harrisburg and EPCOR Water Services. As shown in Figures 6 and 7, increasing the volume of acidic methanol solution significantly increased the methylation efficiency of four trihaloacetic acids. The results on Br3AA were not obtained at EPCOR Water Services

because of the absence of the Br3AA peak, as noted by other studies (Munch et al, 2000). With 3.0 mL of acidic methanol solution, the methylation efficiencies for C13AA, BrCl2AA, ClBr2AA, and Br3AA were significantly increased (at 50°C for 2 h). For Br3AA, a 252% increase in normalized peak area ratio was observed with 3 mL of acidic methanol (Figure 6). This indicated that only 28% of Br3AA was methylated using the methylation conditions under method 552.2. Increasing the acidic methanol reduces the MTBE extraction efficiency for HAA methyl esters. Because no methylation benefit was achieved for mono- and dihaloacetic acids, their normalized peak areas or peak area ratios were reduced. With 4 mL of acidic methanol, the decrease in normalized peak areas for C13AA, BrCl2AA, and ClBr2AA were also observed in Figure 7. Again, this indicated that the decrease in extraction efficiency outweighed the increase in methylation efficiency for these HAAs. At Penn State Harrisburg, Na2S04 was used to replace NaHC03 during the extraction after methylation. This may minimize the loss of HAA methyl esters attributable to the purge of carbon dioxide gas formed by the reaction between NaHC03 and H2S04 (La Guardia, 1996).

In method 552.2 (USEPA, 1995), only 1 mL of acidic methanol was used for 3 mL of MTBE extract, whereas in method 552.1 (USEPA, 1992), 4 mL of acidic methanol

120 NOVEMBER 2002 | JOURNAL AWWA • 94:1 1 | PEER-REVIEWED | XIEETAL



was used for every 2.5 mL of MTBE (equivalent to 4.8 mL of acidic methanol for 3 mL of MTBE extract). In the study reported by Xie and colleagues (Xie et al, 1998), 2 mL of acidic methanol was used for 1 mL of MTBE extract (equivalent to 6 mL of acidic methanol for 3 mL of MTBE extract). On the basis of the results from the study described here, the authors suggest that the volume of acidic methanol be increased from 1 mL to 3 mL for 3 mL of MTBE extract. More studies should be conducted to further optimize the volume of acidic methanol and minimize its effect on mono- and dihaloacetic acids.

Possible solutions for acidic methanol methylation. Because of incomplete methylation of trihaloacetic acids and dalapon, it is important to have the same methylation conditions for HAA samples and standards. In many laboratories, only one continuing calibration check is extracted for each batch of samples. These checks are designed to calibrate the instrument but not methylation efficiency. This practice may have little effect on mono- and dihaloacetic acids. With incomplete methylation of trihaloacetic acids, however, a slight change in methylation conditions, e.g., methylation temperature, time, and volume and formula of acidic methanol, could significantly affect methylation efficiency and analytical results. Therefore, the authors suggest that calibration curves be prepared for each batch of samples when the current methylation conditions in method 552.2 are used.

The methylation efficiency using method 552.2 could be significantly improved for trihaloacetic acids. Increas- ing methylation time increases methylation efficiency but also increases the sample preparation time. Many laboratories, especially commercial laboratories, are unlikely to adopt a longer methylation time. Based on the results from this study, the most effective measure is to increase the volume of acidic methanol. The authors suggest that the volume of acidic methanol be increased from 1 mL to 3 mL for every 3 mL of MTBE extract.

Although increasing methylation temperature could improve the methylation efficiency for trihaloacetic acids, it could also cause more decarboxylation of trihaloacetic acids, especially for Br3AA (Pawlecki-Vonderheide et al, 1997). A study by USEPA (Munch et al, 2000) reported that the use of tert-amyl methyl ether (TAME) as the solvent and 60°C as the methylation temperature significantly improved methylation efficiency for trihaloacetic acids. Because of the

FIGURE 8 Effect of methylation temperature on methylation of six haloacetic acids (conducted at The Pennsylvania State University at Harrisburg)

- CIAA 0 CI2AA - CI3AA - v- BrCI2AA

CIBr2AA - o - Br3AA 1.6-1

0 CO

1.2- S CIAA 4 ' •• - - -• H Q) ▼ - - .-=• • • y

= 0.8- 1 0 z

cr 0.4-

1 1 1 45 50 55

Methylation Temperature - °C 1 mL acidic methanol per millilitre methyl tertiary butyl ether extract, CIAA - monochloroacetic acid, CIÂ - dichloroacetic acid, CljAA - trichloroacetic acid, BrCIÂ - bromodichloroacetic acid, CIBrÂ - chlorodibromoacetic acid, BrjAA - tribromoacetic acid

low boiling point of MTBE (55.2°C), TAME, with a boiling point of 86.3°C, was used for HAA methylation at 60°C. However, the authors found that increasing temperature did not significantly improve methylation efficiency for trihaloacetic acids when 1 mL of acidic methanol per mL of MTBE extract was used (Figure 8) because of the near-complete methylation at 50°C.

Further study is needed to improve or optimize the methylation efficiency of trihaloacetic acids using acidic methanol. Additional research is needed on methylation conditions, including temperature, time, and volume and formula of acidic methanol, as well as the effects of water contained in MTBE or HAA concentration on HAA methylation efficiency. Other conditions, e.g., water sample extraction, MTBE extract neutralization, and HAA chromatographic separation, should be investigated. Many laboratories have reported the disappearance of Br3AA, and this instability must be studied before Br3AA can be accurately reported. The instability of Br3AA may be attributable to the formation of peroxides in aged MTBE solvent (Munch, 2000).

CONCLUSIONS • When the methylation conditions specified under

USEPA method 552.2 were used, a complete methyl-




ation was observed for two monohaloacetic acids and three dihaloacetic acids but not for the four trihaloacetic acids, dalapon, and the surrogate (2,3-dibromopropionic acid). This could significantly affect the analysis of trihaloacetic acids, especially brominated trihaloacetic acids.

• Variation of methylation time, methylation temperature, and volume and formula of acidic methanol significantly affected the methylation efficiency of trihaloacetic acids.

• When method 552.2 is used, the authors suggest that calibration curves be prepared with each batch of samples.

• Methylation efficiency under method 552.2 could be significantly improved by increasing the volume of the acidic methanol from 1 mL to 3 mL for every 3 mL of MTBE extract.

• Further study is needed to improve or optimize the sample extraction, concentration, and methylation processes under USEPA method 552.2.

ACKNOWLEDGMENT

The authors thank Penn State Capital College Research Council, EPCOR Water Services, and Agilent Technologies Inc. for supporting this joint research project. Portions of this article were presented at the 2000 AWWA Water Quality Technology Conference in Salt Lake City, Utah.

ABOUT THE AUTHORS: Yuefeng Xies is an associate professor of environmental engineering in the School of Science, Engineering , and Technology, The Pennsylvania State University at Har-

risburg, 777 W. Harrisburg Pike , Middletown, PA 17057 , e-mail [email protected]. Xie holds BS , MS,

WUHBM and PhD degrees from Tsinghua KXmBjgg University, Beijing, China, and has

more than 1 5 years of research expe- rience in disinfection by-product analysis and control. Inni Rashid is a lab scientist at EPCOR Water Ser-

vices in Alberta. Haojiang ("Joe") Zhou is an environmental engineering designer at Entech Engineering Inc. in Reading, Pa. Leslie Gammie is director of quality assurance for EPCOR Water Services.

FOOTNOTES 'HP 6890, Agilent Technologies Inc., Wilmington, Del. 2HP 5973, Agilent Technologies Inc., Wilmington, Del. 3HP 6890, Agilent Technologies Inc., Wilmington, Del. 4HP 5890, Agilent Technologies Inc., Wilmington, Del. 5To whom correspondence should be addressed

If you have a comment about this article, please contact us [email protected].

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ACIDIC METHANOL methylation for HAA ANALYSIS: LIMITATIONS AND POSSIBLE SOLUTIONS