Quantification of Nine Haloacetic Acids Using Gas Chromatography

Chapter 22

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Quantification of Nine Haloacetic Acids Using Gas Chromatography with Electron Capture Detection Katherine S. Brophy, Howard S. Weinberg, and Philip C . Singer Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, N C 27599

The E P A promulgated Stage 1 of the Disinfectant/Disinfection B y Product Rule in December 1998. Under this rule, five of the nine bromine- and chlorine-containing haloacetic acids (monochloroacetic acid [ M C A A ] , dichloroacetic acid [ D C A A ] , trichloroacetic acid [TCAA], monobromoacetic acid [ M B A A ] , and dibromoacetic acid [DBAA]) were regulated for the first time. Research has shown, however, that the four unregulated species may in fact be formed at significant levels in certain types of chlorinated waters. Hence, future E P A regulations may include these species. This research was aimed at adapting current methodologies to establish a more reliable, sensitive method that can quantify all nine HAA species.

Stage 1 of the Disinfectant/Disinfection By-Products (D/DBP) rule was promulgated in December 1998. (/). Stage 1 set the Maximum Contaminant Level ( M C L ) for five haloacetic acids ( H A A 5 ; monochloroacetic acid [ M C A A ] , dichloroacetic acid [DC A A ] , trichloroacetic acid [TCAA], monobromoacetic acid [ M B A A ] , and dibromoacetic acid [DBAA]) at 60 μg/L. Studies have shown, however, that the four haloacetic acid ( H A A ) species that are not regulated under this rule (bromochloroacetic acid [ B C A A ] , bromodichloroacetic acid [ B D C A A ] , dibromochloroacetic acid [ D B C A A ] , and tribromoacetic acid [TBAA]) may in fact contribute significantly to total H A A concentrations, particularly in high bromide waters. For this reason, Stage 2 of the D/DBP rule may include M C L s for all nine bromine- and chlorine-containing H A A species. Studies performed in our laboratory indicated that Standard Method 625 IB in its current form (2), which uses © 2000 American Chemical Society

In Natural Organic Matter and Disinfection By-Products; Barrett, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

343

344 diazomethane as a derivatizing agent to measure H A A 6 (HAA5 plus B C A A ) , could not effectively measure the remaining three H A A species (HAA3). The method exhibited poor derivatization efficiency for H A A 3 , and poor precision between duplicate samples. E P A Method 552.2 (J), which uses acidic methanol as the derivatizing agent, was also evaluated in our laboratory. While this method was reproducible for H A A 3 , the derivatization efficiency was low, with resulting inadequate quantitation limits. Due to the need for a more reliable, sensitive method for the quantification of all nine bromine- and chlorine-containing H A A species, this research was aimed at adapting current methodologies so that they could be used for analysis of H A A 9 in our laboratory.


Materials and Methods Haloacetic acids were analyzed using modified versions of both E P A Method 552.2 (J) and Standard Method 625IB (2). Twenty-milliliter aliquots of water were extracted at p H < 2 into 4 mL of methyl ί-butyl ether (MtBE) containing internal standard. The extraction was facilitated by the addition of approximately 12 g of anhydrous sodium sulfate, which had been previously baked at 400°C for a minimum of 4 h. The extracted acids were derivatized using either acidic methanol (EPA Method 552.2) or diazomethane (Standard Method 625IB), to form their methyl ester derivatives. The derivatized acids were analyzed on an HP-5890 Series II gas chromatograph equipped with an electron capture detector (Hewlett-Packard, San Fernando, C A ) . Helium (99.999% purity) was used as the carrier gas and nitrogen (99.999% purity) was used as the make-up gas. Gas chromatographic conditions were as follows: Column: DB-1701 fused silica capillary (J&W Scientific, Folsom, CA), 30 m length, 0.25 mm internal diameter, 1 pm film thickness. Temperature program: Initial = 35°C for 10 min, ramp to 75°C at 5°C/min and hold for 15 min, ramp to 100°C at 5°C/min and hold for 5 min, ramp to 135°C at 5°C/min and hold for 10 min. Injector: temperature = 180°C, injection volume = 2 pL, split valve opened at 0.5 min. Detector: temperature = 280-300°C. Gas flow: helium = 1-1.5 mL/min, nitrogen = 40-60 mL/min. High purity H A A standards were obtained from Supelco, Inc. (Bellefonte, P A ) . H A A 6 were purchased as a mixture containing 2 mg/mL of each species dissolved in M t B E , whereas the H A A 3 standards were purchased as neat standards. Single component stock solutions of the H A A 3 species were prepared in M t B E at concentrations ranging from 4-7 mg/mL. Haloester standards were also purchased as a mixture of H A A 6 in M t B E and H A A 3 as neat standards. The surrogate recovery standard, 2,3-dibromopropionic acid, was purchased from Supelco, Inc. as a single component stock solution (1 mg/mL) in M t B E . The internal standard, 1,2,3trichloropropane, was purchased as a neat standard from Aldrich Chemical Co. (Milwaukee, WI). Stock solutions of the internal standard were prepared in M t B E at concentrations ranging from 4-5 mg/mL. A l l stock solutions were stored in a freezer at -15°C and replaced every three months, or upon evidence of degradation. Standard degradation was recognized by a decrease in detector response for the



345 standard at a given concentration over time, and/or the appearance of extraneous chromatographic peaks when the pure standard was analyzed. pH-adjusted solutions were prepared using either a phosphate buffer (pH 7) or a borate buffer (10). The buffer solutions were prepared as described in the CRC Handbook of Chemistry and Physics (4) by adding 0.1 molar sodium hydroxide to 50 mL of 0.1 molar potassium dihydrogen phosphate (pH 7) or 0.025 molar borate (pH 10). Five m L of buffer was added per liter of water, and 0.1 molar sodium hydroxide or 0.1 molar hydrochloric acid was used to achieve the target p H , i f necessary. A l l synthetic waters were prepared using deionized, organic-free laboratory-grade water (LGW) (Dracor Inc., Durham, NC). The toxicity and carcinogenicity of each reagent used in these methods have not been precisely defined. Each chemical should be treated as a potential health hazard. Certain individuals may experience adverse effects upon exposure to the extraction solvent, M t B E , via skin contact or inhalation of vapors. Protective clothing and gloves should be used when handling M t B E , and the solvent should be handled in a fume hood or glove box. Diazomethane is a toxic and explosive gas. Diazomethane should be stored in the freezer at -15°C when not in use. The gas should not be allowed to come in contact with ground glass joints. Protective clothing and gloves should be used when handling diazomethane, and diazomethane should only be handled in a fume hood or glove box.

Method Development Current applications of Standard Method 625IB (2) and E P A Method 552.2 (3) in our laboratory yielded near 100% recovery from water for H A A 6 and near 100% conversion from acid to ester during derivatization, permitting a practical quantitation limit (PQL) for each species of 1 μg/L. The P Q L is defined as the concentration at which a consistent, linear chromatographic response is observed as compared to a standard calibration curve. In examining the efficiencies of the two derivatizing agents in esterifying the H A A 3 species, however, the percent conversions from acid to ester were found to be much lower. Conversion efficiencies were determined by comparing calibration curves built from ester standards to curves built from acid standards that had been extracted from water and derivatized using either diazomethane or acidic methanol. Values on the abscissa scale of these curves reflect the theoretical ester concentration of the derivatized acid standards assuming 100% extraction and conversion efficiency. The ordinate axis represents the relative area of the analyte as measured by the ratio of the analyte peak area to internal standard. Since the latter may change with each fresh batch of extracting solvent, relative areas for a specific analyte concentration may change with each new batch extraction or between experiments. The conversion efficiencies of diazomethane and acidic methanol in esterifying H A A 3 were compared in order to decide which method to pursue in terms of optimization for H A A 3 analysis. Examples of the conversion efficiencies of the two derivatizing agents in esterifying H A A 3 are shown in Figures 1-4. While the conversion efficiency is good for B D C A A (near 100%), the conversion efficiencies for D B C A A and T B A A are


Relative Peak Area

346

2

Ester Standard

1.5 " 1 Derivatized Acid 0.5 0 '

1

0

1

15

1

30

60

45


Concentration (^g/L) Figure 1. Average derivatization efficiency for BDCAA

6 ι

Concentration (pg/L) Figure 2. Average derivatization efficiency for DBCAA

2.5 ι

0

15

30

45

60

75

Concentration (^g/L) Figure 3. Average derivatization efficiency for TBAA using diazomethane



347 low, approximately 25% and 30%, respectively. The conversion efficiencies of both agents were similar for B D C A A and D B C A A , but diazomethane was slightly better than acidic methanol at converting T B A A to its corresponding ester (Figure 3 versus Figure 4). This may be due to the fact that T B A A can undergo partial decarboxylation to form bromoform upon exposure to methanol (5), thereby lowering conversion to ester of this species by acidic methanol. Figures 2 and 3 demonstrate that the derivatizing agents were less than effective in quantitatively esterifying D B C A A and T B A A , respectively. Due to the limitations of acidic methanol in esterifying T B A A , as well as the laborious and time-consuming nature of the acidic methanol process, it was decided to pursue the diazomethane method in terms of optimization for H A A 3 . A n examination of each step in the procedure revealed a detrimental impact on the esterification of H A A 3 caused by the presence of water co-extracted with the analytes into the M t B E prior to derivatization. Little is known regarding the relative reaction rates of H A A 6 , H A A 3 , and water with diazomethane. A possible explanation for the detrimental impact of water on H A A 3 esterification is that the bulky molecular size and structure of the H A A 3 species as compared to the H A A 6 species result in slower rates of esterification for H A A 3 . Since water reacts with diazomethane to form methanol and nitrogen gas, dissolved water in the extracts exhibits a demand on diazomethane when the derivatizing agent is added. A s a result, the diazomethane may become depleted to the extent that esterification of H A A 3 becomes kinetically hindered before 100% conversion has occurred. Kinetic studies on the rates of esterification for H A A 6 , H A A 3 , and water were beyond the scope of this research, thus this hypothesis cannot be supported by kinetic data at this time. Various approaches towards removing dissolved water from the M t B E extracts were considered, mainly focusing on treating the M t B E with a drying agent prior to derivatization. Standard Method 625IB (2) suggests the option of filtering the extracts through acidified sodium sulfate (Na S0 ) to remove water before esterification. A simplified version of this drying step was evaluated for H A A 3 in our laboratory, using anhydrous magnesium sulfate (MgS0 ) as the drying agent. Disposable glass Pasteur pipettes were fitted with glass wool, and approximately one gram of M g S 0 was placed on top of each glass wool plug. The M t B E extracts were filtered through the salt, and 2 m L of each sample was collected in 2-mL volumetric flasks for derivatization. The results of this experiment for D B C A A and T B A A are shown in Figure 5 and Figure 6, respectively. As can be seen, poor recovery was obtained for these species, most likely due to adsorption of the analytes onto the surface of the glass wool. For this reason, an alternative approach was evaluated to remove water from the M t B E . Rather than filtering the extracts through the salt, approximately 100 mg of M g S 0 was added directly to each extract prior to addition of diazomethane. This method of water removal allowed near 100% esterification of H A A 3 , as illustrated in Figures 79. A drawback to the addition of the drying step to the procedure was the creation of a peak due to a reaction between sulfate and diazomethane. A similar peak, tenta tively identified as dimethyl sulfide, is observed using E P A Method 552.2 (3). When the modified diazomethane method was evaluated in terms of H A A 9 , it was found 2

4

4

4

4


348


Concentration (pg/L) Figure 4. Average derivatization efficiency for TBAA using acidic methanol

1.5 η

0

25

50

75

Concentration ^ g / L )

Figure 5. Derivatization efficiency for DBCAA when fdtered through MgS0

4

Concentration ^ g / L )

j

Figure 6. Derivatization efficiency of TBAA when filtered through MgS0

4


349


Concentration (pg/L) Figure 7. Derivatization efficiency ofBDCAA — MgS0 added to extract 4

Concentration (pg/L) Figure 8. Derivatization efficiency for DBCAA — MgS0 added to extract 4

j

Concentration (pg/L)

|

Figure 9. Derivatization efficiency for TBAA — MgS0 added to extract 4


350 that this peak co-eluted with B C A A when using a DB1701 column. At concentrations above 5 μg/L of B C A A , resolution between the two peaks allowed quantitation of B C A A . Below 5 μg/L, however, the B C A A peak became engulfed by the dimethyl sulfide peak. In order to rectify this problem, several alternative capillary columns were considered. It was found that use of a DB-1 column (30 m, 0.25 mm, 1 μηι) allowed resolution of all nine H A A species, as well as the surrogate and internal standards. The temperature program using the DB-1 column was as follows: Initial temperature = 37°C, hold for 21 min, ramp to 136°C at 5°C/min, hold for 3 min, ramp to 250°C at 20°C/min, hold for 3 min. Using the adapted method with M g S 0 added to the derivatization flask and the DB-1 column for separation, all nine H A A species could be consistently quantified, with a P Q L of 1 μg/L for all nine species. Downloaded by COLUMBIA UNIV on July 31, 2012 | http://pubs.acs.org Publication Date: August 15, 2000 | doi: 10.1021/bk-2000-0761.ch022

4

Removal of Chlorine Five chlorine-quenching agents were evaluated to determine the best choice for removal of chlorine while stabilizing levels of formed H A A 9 : ammonium chloride (NH C1), ammonium sulfate ((NH ) S0 ), sodium sulfite (Na S0 ), sodium thiosulfate (Na S 0 ), and sodium meta-arsenite (NaAs0 ). E P A Method 552.2 (J) and Standard Method 625IB (2) both call for the use of NH C1. However, all five quenching agents have been used in the literature to quench chlorine for disinfection by-product analysis. The quenching agents were evaluated on a mixture of H A A 9 prepared in L G W in 40-mL vials at temperature conditions simulating what might occur during sample collection in the field and at two p H values (7 and 10). Approximately 10 mg of quenching agent was added to each 40-mL vial (except the control), making a final concentration of approximately 250 mg/L. The results of the evaluation for the sum of H A A 9 are illustrated in Figures 10 and 11, along with the conditions employed, and indicate that either NH C1, ( N H ) S 0 or N a A s 0 could be used as a quenching agent without affecting overall H A A 9 stability. In examining the impacts of the quenching agents on individual H A A species, ( N H ) S 0 appeared to least impact H A A stability and was therefore chosen as the quenching agent to be used during field sample collection. 4

4

2

2

2

4

2

3

3

2

4

4

4

2

4

2

4

2

4

Quality Assurance The adapted method for H A A analysis was quality assured by conducting split sampling analyses with two other laboratories each using their own quality assured method. Lab #2 uses E P A Method 552.2 (3) for H A A 9 analysis, and Lab #3 uses Standard Method 625IB (2). The water used in these tests was collected from a drinking water utility treating low-bromide surface water. Upon receipt of a settled water sample at the U N C laboratories, the water was spiked with 300 μg/L bromide then chlorinated with 7 mg/L C l (Sample A). Residual chlorine was quenched using approximately 250 mg/L ammonium sulfate, and aliquots of Sample A were adjusted to p H 6 and p H 10 and spiked with approximately 10 μg/L of each H A A 9 species 2



351

Figure 10. Impact of quenching agents on HAA stability—24 h at 15°C, 2 weeks at 4°C

Figure 11. Impact of quenching agents on HAA stability—24 h at 15°C, 2 weeks at 4°C


352


(Samples Β and C, respectively). Each sample had 10 mg/L of sodium azide, evaluated elsewhere (tf), added prior to shipping to the participating laboratories to prevent biodégradation of the haloacetic acids prior to analysis. The split sampling results are illustrated in Table I and illustrate a few trends of note. When using acidic methanol, the calculated level of M C A A in Sample A is more than double that obtained by diazomethane and appears to be divergent from the true value for Sample C. Acidic methanol appears to demonstrate an underestimation for C D B A A and T B A A at low levels (Sample A ) , while the existing standard method overestimates B D C A A . This inconsistency among the established methods, especially at lower levels of H A A s , illustrates the need to establish a standard methodology for H A A 9 analysis so that all laboratories analyzing for H A A 9 can achieve consistent, accurate results. The adapted method was used to determine spike recoveries for H A A 9 in several different matrices in order to ascertain that matrix effects would not prevent accurate quantitation of all nine species. One spike recovery study was performed on water collected from the point-of-entry (POE) to the distribution system at a water utility which treats low-bromide surface water from the Mississippi River. The results for the spike recovery are shown in Table II, demonstrating good spike recoveries for all species and indicating that accurate results can be obtained using the adapted methodology. Table II also indicates that the currently unregulated H A A 3 species account for over 10% of the total H A A 9 concentrations, even in a low bromidecontaining water. This further demonstrates the need for a more reliable methodology for the quantitation of all nine H A A species that can be easily deployed in the drinking water industry. The method detection limit ( M D L ) was also evaluated using the adapted methodology. A solution was prepared containing 1 μg/L of each H A A species in water, and seven replicates were extracted and derivatized using the adapted methodology. The M D L was determined by multiplying the standard deviation between the seven replicates for each species by the student's t-value at 99% confidence and n-1 degrees of freedom (3.143 for seven replicates). The results of this study are shown in Table III. For all H A A 9 species, the relative standard deviation was less than or equal to 10%. This demonstrates the ability of the adapted methodology to provide accurate, precise results, even at low levels of H A A 9 .

Conclusions This research resulted in the establishment of an analytical method that can more reliably quantify all nine bromine- and chlorine-containing H A A species in chlorinated waters at levels as low as 1 μg/L. B y removing water from M t B E extracts with M g S 0 prior to derivatization, nearly 100% conversion of each acid to its corresponding ester can be achieved. Use of a DB-1 capillary column permits complete resolutions of all nine H A A s , the surrogate recovery standard, and the internal standard. Samples collected in the field are quenched of residual chlorine with ( N H ) S 0 , which does not impact the levels of H A A 9 present in the range of pH 7-10. 4

4

2

4


353


Table I. Split Sampling for HAA9 Analysis CDBAA

TBAA

10.9 11.4 15 12.4 2.24 18%

11.7 10.0 12 11.2 1.08 10%

4.7 3.2 4.7 4.20 0.87 21%

16.7 18.4 21 18.7 2.17 12%

21.7 22.3 27 23.7 2.90 12%

21.1 19.4 23 21.2 1.80 9%

16.9 16.6 19 17.5 1.31 7%

16.3 18.6 19 18.0 1.46 8%

21.3 22.5 27 23.6 3.00 13%

20.7 19.5 24 21.4 2.33 11%

16.5 16.6 19 17.4 1.42 8%

Sample

MCAA MBAA DCAA BCAA TCAA DBAA BDCAA

A-UNC A -Lab #2 A -Lab #3 Average St. Dev. % RSD

2.01 B D L * 1.7 5.5 BDL** 2.2 3.76 1.95 2.47 0.35 66% 18%

3.4 5.9 4.9 4.73 1.26 27%

6.79 9.1 9.0 8.30 1.31 16%

3.18 3.7 4.6 3.83 0.72 19%

6.09 9.1 10 8.40 2.05 24%

12.1 12.6 13 12.6 0.45 4%

14.2 17.2 15 15.5 1.55 10%

17.7 19.8 20 19.2 1.27 7%

14.1 15.2 16 15.1 0.95 6%

14.0 18.5 16 16.2 2.25 14%

17.4 20.3 20 19.2 1.59 8%

13.7 15.6 16 15.1 1.23 8%

B-UNC Β -Lab #2 Β -Lab #3 Average St. Dev. % RSD

11.2 12 11 11.4 0.53 5%

12.4 C-UNC 11.7 C -Lab #2 8.9 12.9 C -Lab #3 12 12 Average 11.1 12.2 St. Dev. 1.92 0.62 % RSD 17% 5% * Detection limit = 1.00 pg/L **Detection limit = 2.00 pg/L

Table II. Spike Recoveries for HAA9 in Sample Matrix Sample

Concentration (pg/L) MCAA

POE

MBAA DCAA

BCAA

TCAA

DBAA

BDCAA

DBCAA

TBAA

100 μg/L.

Acknowledgments This paper represents a part of an on-going study into the formation, occurrence, stability, and dominance of haloacetic acids and trihalomethanes in treated drinking water. The research is funded by the American Water Works Association Research Foundation.

Literature Cited 1. U.S. Environmental Protection Agency. National Primary Drinking Water Reg ulations: Disinfectants and Disinfection Byproducts. Fed. Reg. 1998, 63 (241), 69389. 2. Eaton, A. D., Clesceri, L. S., Greenberg, A. E., Eds. Standard Methods for the Examination of Water and Wastewater, 19th Edition. A P H A : Washington, DC, 1995; pp 6-67 to 6-76.


355 3.

4. 5.


6.

Munch, D. J.; Munch, J. W.; Pawlecki, A. M. Method 552.2: Determination of Haloacetic Acids and Dalapon in Drinking Water by Liquid-Liquid Extraction, Derivatization and Gas Chromatography with Electron Capture Detection. U.S. Environmental Protection Agency: Cincinnati, OH, 1995; pp 552.2-1 to 552.2-34. Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 76th Edition. CRC Press: Boca Raton, FL, 1995; p 8-42. Peters, R. J. B.; Erkelens, C.; de Leer, E. W. B.; de Galan, L. Wat. Res. 1991, 25, 473-477. Brophy, K. S. M.S. Thesis, University of North Carolina, Chapel H i l l , NC, 1999.


Quantification of Nine Haloacetic Acids Using Gas Chromatography

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