Research Articles
NDMA in Drinking Water
N-Nitrosodimethylamine in Drinking Water Using a Rapid, Solid-Phase Extraction Method Stephen W. D. Jenkins l, Carolyn J. Koester2, Vincent Y. Taguchi t, David T. Wang 1, Jean-Paul F. P. Palmentier1, Kim P. Hong 1 1 Ministry of Environment and Energy, Laboratory Services Branch, 125 Resources Road, Etobicoke, Ontario, MgP 3V6, Canada 2 Present address: Lawrence Livermore National Laboratory, Chemistry and Materials Science Division, University of California, Livermore, California, 94551, USA
Corresponding author: Vincent Y. Taguchi, Ph. D., Supervisor, Mass Spectrometry Laboratory
Abstract A simple, rapid method for the extraction of N-nitrosodimethylamine (NDMA) from drinking and surface waters was developed using Ambersorb 572. Development of an alternative method to classical liquid-liquid extraction techniques was necessary to handle the workload presented by implementation of a provincial guideline of 9 ppt for drinking water and a regulatory level of 200 ppt for effluents. A granular adsorbent, Ambersorb 572, was used to extract the NDMA from the water in the sample bottle. The NDMA was extracted from the Ambersorb 572 with dichloromethane in the autosampler vial. Method characteristics include a precision of 4 % for replicate analyses, an accuracy of 6 % at 10 ppt and a detection limit of 1.0 ppt NDMA in water. Comparative data between the Ambersorb 572 method and liquid-liquid extraction showed excellent agreement (average difference of 12 %). With the Ambersorb 572 method, dichloromethane use has been reduced by a factor of 1,000 and productivity has been increased by a factor of 3 - 4. Monitoring of a drinking water supply showed rapidly changing concentrations of NDMA from day to day.
Key words: NDMA; extraction method, rapid, solid-phase; Ambersorb 572
1
Introduction
N-nitrosodimethylamine (NDMA), Chemical Abstracts Service Registry Number [62-75-9], is a known carcinogen [1 - 3]. Tbe presence of NDMA is associated with many different industrial processes. It has been measured in air samples taken at tire factories and tanneries [4] and at metalworking factories [5]. NDMA is often found in food products such as beer [6] and cured meats [7, 8], and tobacco smoke [9]. NDMA has also been found in drinking water [ 1 0 - 13], surface water [14], and sea water [15]. NDMA may also be formed, under acidic conditions, by the reaction of amines with nitrites. As a result of finding NDMA in a drinking water supply in 1989 [16], the Ministry of Environment and Energy (MOEE) established a drinking water guideline of 9 ppt [18] and a regulatory limit of 200 ppt for effluents. To handle the workload resulting from monitoring NDMA for exceedences of the drinking water guideline and the
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 207-210 (1995) 9 ecomed publishers, D-86899 Landsberg, Germany
regulatory level for effluents, a new sample preparation method had to be developed. Previously, liquid-liquid extraction, the most common extraction method for removing NDMA from liquid matrices, was used [10, 14, 17, 19]. Some methods of NDMA analysis have used solid phase extraction (SPE) with various adsorbents including Amberlite XAD-2 resin [11], Ambersorb XE-340 [12], and other carbonaceous materials [10, 13, 15]. In this laboratory, a method of extraction was developed based on a granular adsorbent, Ambersorb 572. Ambersorb 572 consists of carbonaceous black, spherical beads that are produced by the pyrolysis of highly sulfonated styrene-divinyl benzene macroreticular ion exchange resin [20]. Initial experiments were performed with Carboxen 564 which was found to be an effective extraction agent. However, because Ambersorb 572 provided comparable NDMA extraction efficiencies and was less expensive than Carboxen 564, a method based on the use of Ambersorb 572 was developed. To simplify solid phase extraction, Ambersorb 572 was added directly to the water samples spiked with the internal standard ds-NDMA. The sample bottles were placed on a roller apparatus for the extraction. The Ambersorb 572, to which NDMA was adsorbed, was isolated by filtration, airdried and transferred to an autosampler vial. Dichloromethane was added to the vial, which was then capped and loaded onto the autosampler tray. The extract was analyzed on a gas chromatograph/high resolution mass spectrometer at a mass resolution of 7,000. To our knowledge, this paper presents the first method in which Ambersorb 572 is added directly to a water sample to effect NDMA extraction.
2
2.1
Experimental
Instrumentation, apparatus and reagents
Instrumentation: The instrumentation has been described in detail elsewhere [21] and is summarized here. A HewlettPackard 5890 Series II gas chromatograph (Hewlett-Packard, 207
NDMA in Drinking Water
Mississauga, Ontario, Canada) was equipped with a split/ splitless injector and a CTC A200S autosampler (Leap Technologies, Chapel Hill, North Carolina, USA). Chromatography was performed with a 30 m x 0.25 mm id, 1/lm film thickness, DB-1701 (J&W Scientific, Folsom, California, USA) column. A VG Analytical ZAB-2F doublefocusing reverse geometry magnetic sector mass spectrometer equipped with a DEC VAXstation 3100 (M76) and VG OPUS2000 (v2.1) software (Fisons, Manchester, UK) was operated in the electron ionization, single ion monitoring mode at 7,000 resolution (10 % valley). Apparatus: A roller apparatus that accommodated 1 L bottles (Hotpack Corporation, Philadelphia, Pennsylvania, USA) was modified with a variable speed control to achieve 50 rpm (Leeson Electric Corporation, Grafton, Wisconsin, USA). Reagents: Ambersorb 572 (Supelco Canada Ltd., Oakville, Ontario, Canada) was conditioned at 320 ~ for 3 hours before use. High purity water was obtained from a reverse osmosis/ion exchange/UV system (Biolab Equipment Canada Ltd., Oakville, Ontario, Canada). 2.2
Ambersorb 572 extraction
A 500 mL aliquot of the sample was transferred to a clean 1 L amber bottle with a Teflon-lined cap. After the addition of the internal standard, d6-NDMA , (15 ppt) and 200 mg of Ambersorb 572 (400/~L, measured in a flatbottom autosampler vial insert), the bottle was rolled at 50 rpm for 1 hour. The contents of the bottle were filtered through filter paper to collect the Ambersorb 572. The filter paper (with the Ambersorb 572) was transferred with forceps to a disposable aluminium dish, where it was allowed to air dry for 3 0 - 6 0 minutes. The dried Ambersorb 572 was transferred to an autosampler vial and 400/IL of dichloromethane were added. The vial was capped with a Teflon-lined crimp cap, tapped to expel air bubbles from the Ambersorb 572, and then loaded onto the autosampler tray for analysis. Procedure blanks were prepared in triplicate by adding d6-NDMA (15 ppt) and 200 mg Ambersorb 572 to 500 mL aliquots of high purity water. The average of the three blanks was used for the blank correction. Spiked control samples were prepared by adding NDMA (10.0 ppt and 200 ppt) to successive 500 mL aliquots of high purity water. To the first bottle were added d6-NDMA (15.0 ppt) and 200 mg Ambersorb 572. To the second bottle were added d6-NDMA (500 ppt) and 200 mg Ambersorb 572. A greater quantity of internal standard was added to adhere to the practice of spiking samples which are expected to contain high NDMA concentrations (ie. effluent samples) with comparable concentrations of internal standard. Additional control samples spiked at 5 ppt, 20 ppt, 40 ppt and 80 ppt NDMA were run with d6-NDMA at 15 ppt.
2.3
Liquid-liquid extraction
Liquid-liquid extraction was performed according to a Ministry of Environment and Energy standard procedure [17]. An 800 mL sample aliquot was transferred to a 1 L separatory funnel and spiked with d6-NDMA (15.8 ppt).
208
Research Articles
The sample's pH was adjusted to 12 with a 50 % sodium hydroxide solution and the solution was serially extracted with dichloromethane. The combined dichloromethane extract was washed with a pH 2 sulphuric acid solution. The washed extract was filtered through granular anhydrous sodium sulphate and then concentrated by rotary evaporator and a nitrogen evaporating unit to approximately 200/IL.
2.4
Instrumental analysis
The detailed procedure has been described elsewhere [21]. The mass spectrometer was tuned to 7,000 resolution with perfluorotributylamine (PFTBA). Solutions of standards having NDMA and d6-NDMA concentrations ranging from 0.50 to 16440 pg injected and 1,3-diethylbenzene (1,3-DEB)(42 pg injected) were transferred to 200/aL conical inserts in the 2 mL autosampler vials which were then capped and loaded onto the autosampler tray. Multi-point calibration curves were generated in 3 segments. All standards contained a fixed amount of 1,3-DEB (42 pg injected) to correct for variability in the instrument sensitivity. NDMA concentrations in the procedure blanks, spiked control samples and samples were calculated by isotope dilution with d6-NDMA. M1 NDMA concentrations in the spiked control samples were corrected for the average NDMA concentration in the three procedure blanks.
3
Results and Discussion
In developing a new method for NDMA analysis, the goals were to increase lab productivity, minimize solvent use, glassware and reagents, number of steps, lower the cost of sample preparation and improve method precision, accuracy and detection limits. The Ambersorb 572 method successfully met all of these goals. It requires only 400/aL of dichloromethane per extraction. By comparison, the liquidliquid extraction method requires 300 mL (including glassware rinses) of dichloromethane per sample. Sodium sulphate, sodium hydroxide, sulphuric acid, separatory funnels, conical funnels and round bottom flasks are not required. The granular nature of the Ambersorb 572 facilitates isolation on filter paper and prevents the autosampler syringe from being plugged. Productivity has been increased to approximately 3 0 - 4 0 samples (including up to 12 QC samples) per person per day. This is a 3- to 4-fold increase with respect to liquid-liquid extraction. Extraction conditions. The mixing speed for the roller apparatus was set at 50 rpm to provide sufficient agitation for the Ambersorb 572 in the bottle and was not investigated further. The 200 mg of Ambersorb 572 were chosen because this amount was easily measured in a vial insert as 400/aL and this amount was compatible with 400/~L dichloromethane in a 2 mL autosampler vial. Using a 500 mL sample size afforded the opportunity to perform replicate analyses on a 1 L water sample.
Extraction time. Figure 1 shows a plot of NDMA and d6-NDMA recovered from 17 water samples (spiked with 40.5 ppt NDMA and 25.1 ppt d6-NDMA) versus minutes rolled with Ambersorb 572. The amount of analyte extracted
E S P R - E n v i r o n . Sci. & Pollut. Res. 2 (4) 1995
Research Articles
N D M A in Drinking Water
by the Ambersorb 572 gradually increased over a period of approximately 50 minutes and then reached equilibrium. However, an equilibrium between the analyte in the water and analyte adsorbed to Ambersorb 572 is not a requirement for accurate quantitation with isotope dilution. EXTRACTION TIME STUDY
0
100
50
150
MINUTES
200
250
ROLLED
I+ ~ N
d6-NDMA
I
2o
o
0
so
,;,~uTEs.od~ ~
~oo
Fig. 1: Plots of NDMA and d6-NDMA recovered from spiked water samples versus minutes rolled with Ambersorb 572. The total amounts of NDMA and d6-NDMA in each 500 mL high purity water sample were 20.3 ng (40.5 ppt) and 12.6 ng (25.1 ppt) respectively. Each point represents a single measurement
relative standard deviations were less than 4 %. Day-to-day precision and accuracy were assessed by averaging all 32 measurements collected during the study period. Measured concentrations and relative standard deviations for the low and high N D M A spikes were 9.63 ppt and 4.2 % and 198 ppt and 3 . 1 % , respectively. Method detection limits and recoveries. Method detection limits and recoveries were also determined by analyzing eight replicate samples (spiked with 10.0 ppt NDMA) per day on four days. The highest method detection limit, defined as three times the standard deviation of replicate measurements [22], calculated for the four day period was 1.0 ppt. This was better than the 1.6 ppt detection limit obtained with the liquid-liquid extraction method [17]. Using data from the above experiments (10.0 ppt NDMA), the within-run average recoveries for N D M A and d6-NDMA were determined to be the same at the 95 % confidence level. Betweenrun recoveries ranged from 26 % to 4 1 % . By comparison, recoveries of N D M A by liquid-liquid extraction have been 20 - 30 % for most samples. This low recovery can be advantageous. Table 1 shows the data generated by serial extractions of 3 water samples spiked with 10.0 ppt NDMA. The average recovery in each extraction was approximately 40 %. The total recovery for the 4 extractions was 89 %. The concentrations of N D M A are the same in all of the extractions. Thus, with the Ambersorb 572 method, it is possible to obtain up to 4 replicate analyses with the same sample. Table 1: Serial extraction of water samples with Ambersorb 572
Figure 2 shows the concentrations of N D M A measured using various extraction times. The concentration of N D M A measured in each sample was independent of the extraction time. Thus, an extraction time of 60 minutes was chosen because it yielded the maximum NDMA recovery in the least amount of time. At 60 minutes, both N D M A and d6-NDMA recoveries were 40 %.
e~
o"
c
8< z
2
5
10
13
16
2O
30
4O
50
8O
~
105
120
150
180
210
Extraction/Rolling Time (minutes)
Fig. 2: Measured NDMA concentrations at varying extraction times. A 500 mL high purity water sample was spiked with 20.3 ng (40.5 ppt) of NDMA and 12.6 ng (25.1 ppt) of d6-NDMA Method precision and accuracy. The method's within day precision and accuracy were determined by analyzing eight replicate samples of high purity water (spiked with 10.0 ppt NDMA) and another eight samples (spiked with 200 ppt NDMA) per day on four days. The daily average N D M A concentrations were within 6 % of the expected values and
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995
Actual NDMA Measured Measured Measured Measured Concentration (pptl NDMA (ppt) NDMA (ppt) NDMA (ppt) NDMA (ppt) Extraction #1 Extraction #2 Extraction 03 Extraction 10.0
9.11+1.0%
9.37+5.2%
9.14___7.1%
Recovery
40 %
24 %
15 %
8.83• 10 %
Comparative studies. The results of 39 pairs of analyses in which drinking and surface waters were extracted by both the Ambersorb 572 method and by liquid-liquid extraction with dichloromethane were compared. A plot of the log of NDMA concentrations measured by the Ambersorb 572 method versus the log of NDMA concentrations measured by liquidliquid extraction is shown in Figure 3. The correlation coefficient (r) is 0.98, indicating that N D M A concentrations measured using Ambersorb 572 extraction and those measured using liquid-liquid extraction are significantly related. The slope of the regression line for this plot is 1.02, which suggests that the N D M A concentrations obtained by the Ambersorb 572 method are comparable to those obtained by liquid-liquid extraction. The differences in concentrations averaged 12 %. Monitoring studies. In 1989, N D M A was found in an Ontario drinking water sample which was collected as part of the province's Drinking Water Surveillance Program [16]. As a consequence of finding elevated levels of N D M A in a series of samples from one location, the ministry set an interim-guideline of 14 ppt in drinking water and a regulatory
209
N D M A in Drinking Water
Research Articles
level of 500 ppt in effluents. In 1990, the ministry revised the drinking water guideline to 9 ppt [18]. In 1992, the regulatory level for effluents was revised to 200 ppt.
Acknowledgements The authors would like to thank Dr. Bill BERGfor the donation of the roller apparatus and Patrick RILEY and Walter OFFENBACHERfor performing the necessary modifications to it. The authors would also like to thank Dr. Ray CLEMENTfor helpful suggestions.
} 2
5
J~ .g" |
1~ 1-$
8
9 9~ 0"5R5
9 R9r" "-%
1
13
2
LogNDMAConccntral~o~by Laquid- L/quidExlraclion(ppl)
2.$
Fig. 3: Plot of the logarithms of NDMA concentrations determined by the Ambersorb method versus the liquid-liquid extraction for 39 samples. The correlation coefficient r is 0.98 and the slope of the regression line is 1.02
Table 2 shows the results of replicate analyses of raw and treated water from a drinking water supply. Concentrations less than the reporting limit (RL) of 5 ppt are listed as not detected [ND (RL)]. These data show that, if the precursors to NDMA are present in the raw water, the treatment process generates NDMA. The data also demonstrate that the concentrations of NDMA can change rapidly from day to day. At the time that NDMA was detected at this location, sampling was being done weekly. Bi-weekly or monthly sampling might have been insufficient to detect NDMA. Therefore, at some locations, there are requirements to sample frequently and to have the capacity to handle a large number of samples once NDMA is detected. Table 2: N D M A Concentrations in a Drinking Water Supply
Date Sampled (Day)
Raw Water (ppt)
Treated Water (ppt)
Jan. 3 (1)
ND (5), ND (5)
ND (5), ND (5)
,Jan. 10 (8)
ND (5), ND (5)
90, 92
Jan. 14 (12)
7, 8
150, 150
Jan. 15 (13)
18, 17
180, 180
Jan. 16 (14)
ND (5), ND (5)
28, 32
Jan. 17 (15)
ND (5), ND (5)
ND (5), ND (5)
4
Conclusions
The performance data and comparative studies have allowed this laboratory to replace the liquid-liquid extraction method with the Ambersorb 572 method in the analysis of NDMA from water. The increase in productivity is a factor of 3 - 4 even though there has been a 6-fold increase in the number of QC samples per batch of samples. The new methodology described in this paper has increased the sample capacity of this laboratory and has allowed frequent monitoring of drinking water supplies should concentrations of NDMA exceed the drinking water guideline or the effluent regulatory limit.
210
References
[1] FREUND, H. A.: Clinical Manifestations and Studies in Parenchymatous Hepatitis. Ann. Intern. Med. 10, 1144 (1937) [2] MAGEE,P. N.; J. M. BARNES:Carcinogenic Nitroso Compounds. Advanc. Cancer Res. 10, 163 (1967) [3] IARC Monograph on the Evaluation of Carcinogenic Risk of Chemicals to Man. 1, 85 (1972) [4] FINE, D. H.; D. P. ROUNBEHLER:Occurrence of N-Nitrosamines in the Workplace. In: R.A. SCANLAN;S. R. TANNENBAUM,(Eds.), ACS Symposium Series, No. 174: N-Nitroso Compounds, Amer. Chem. Soc., 1981, p. 207 [5] FADLALLAH,S.; S. F. COOPER; M. FOURNIER;D. DROLET;G. PERRAULT: Determination of N-nitroso Compounds in the Environment of a Metal Factory Using Metalworking Fluids. Int. J. Environ. Anal. Chem. 39, 281 (1990) [6] S E N , N . P . ; S. S E A M A N : Gas-Liquid Chromatographic-Thermal Energy Analyzer Determination of N-Nitrosodimethylamine in Beer at Low Parts per Billion Level. J. Assoc. Off. Anal. Chem. 64, 933 (1981) [7] HAVERY,D. C.; T. FAZ10;J. W. HOWARD:Survey of Cured Meat Products for Volatile N-Nitrosamines: Comparison of Two Analytical Methods. J. Assoc. Off. Anal. Chem. 61, 1374 (1978) [8] HOTCHKISS,J. H.; L. M. LJBBEY;J. F. BARBOUR;R. A. SCANLAN: Combination of a GC-TEA and a GC-MS-Data System for tbe /~g/kg Estimation and Confirmation of Volatile N-Nitrosamines in Foods. IRAC Sci. Publ. 10, 361 (1980) [9] DRUCKREY,H.; R. PREUSSMANN:Zur Entstehung carcinogener Nitrosamine am Beispiel des Tabakrauchs. Naturwiss. 49, 498 (1962) [10] FINE, D. H.; D. P. ROUNBEHLER;F. HUFFMAN;A. W. GARRISON; N. L. WOLFE;S. S. EPSTEIN:Analysis of Volatile N-Nitroso Compounds in Drinking Water at the Part per Trillion Level. Bull. Environ. Contam. Toxicol. 14, 404 (1975) [11] NIKAIDO,M. M.; D. DEAN-RAYMOND;A. J. FRANCIS;M. ALEXANDER: Recovery of Nitrosamines from Water. Water Res. 11, 1085 (1977) [12] KIMOTO, W . I . ; C . J . DOOLEY; J. CARRfl; W. FIDDLER: Nitrosamines in Tap Water After Concentration by a Carbonaceous Adsorbent. Water Res. 15, 1099 (1981) [13] KUL'BICH,T. S.; L. A. TIKTIN; A. A. GLAVIN: Sorptive Concentration as a Method for Improving Sensitivity of Determination of Nitrosamines in Water. J. Anal. Chem. USSR. 44, 1289 (1989) [14] FINE, D . H . ; D.P. ROUNBEHLER: N-Nitroso Compounds in Water. In: L . H . KEITH (Ed.), Identification & Analysis of Organic Pollutants in Water, Ann Arbor Science Publ. Inc, Ann Arbor, Michigan 1976, p. 255 [15] KADOKAMI,K.: Trace Analysis of Water-Soluble Compounds Using Activated Carbon Extraction Method. PPM. 22, 37 (1991) [16] Ministry of Environment and Energy (MOEE): Scientific Criteria Document for Multimedia Standard Development No. 01 - 90: N-Nitrosodimethylamine, ISBN 07729-8318-6. March (1991) [17] Ministry of Environment and Energy: The Determination of NNitrosodimethylamine (NDMA) in drinking Water and in Aqueous Samples by Gas Chromatography/High Resolution Mass Spectrometry, LSB Method MSABN-E3291A. (1993) [18] Ministry of Environment and Energy: Ontario Drinking Water Objectives, 5th Edition. (1994) [19] Method 607-Nitrosamines. (EPA) Federal Register: 49, 81 (1984) [20] Supelco, Inc: Ambersorb 572 Data Sheet (DS710085). (1990) [21] TAGUCHI, V. Y.; S. W., D. JENKINS; D. T. WANG; J.-P. F. P. PALMENTIER; E . J . REINER: The Determination of Nnitrosodimethylamine by Isotope Dilution High Resolution Mass Spectrometry. Can. J. Appl. Spectrosc. 39, 878 (1994) [22] TAYLOR,J. K: Quality Assurance of Chemical Measurements. Lewis Publishers, Inc. Chelsea, Michigan 1987 Received: April 18, 1995 Accepted: August 22, 1995
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995
NDMA in Drinking Water
N-Nitrosodimethylamine in Drinking Water Using a Rapid, Solid-Phase Extraction Method Stephen W. D. Jenkins l, Carolyn J. Koester2, Vincent Y. Taguchi t, David T. Wang 1, Jean-Paul F. P. Palmentier1, Kim P. Hong 1 1 Ministry of Environment and Energy, Laboratory Services Branch, 125 Resources Road, Etobicoke, Ontario, MgP 3V6, Canada 2 Present address: Lawrence Livermore National Laboratory, Chemistry and Materials Science Division, University of California, Livermore, California, 94551, USA
Corresponding author: Vincent Y. Taguchi, Ph. D., Supervisor, Mass Spectrometry Laboratory
Abstract A simple, rapid method for the extraction of N-nitrosodimethylamine (NDMA) from drinking and surface waters was developed using Ambersorb 572. Development of an alternative method to classical liquid-liquid extraction techniques was necessary to handle the workload presented by implementation of a provincial guideline of 9 ppt for drinking water and a regulatory level of 200 ppt for effluents. A granular adsorbent, Ambersorb 572, was used to extract the NDMA from the water in the sample bottle. The NDMA was extracted from the Ambersorb 572 with dichloromethane in the autosampler vial. Method characteristics include a precision of 4 % for replicate analyses, an accuracy of 6 % at 10 ppt and a detection limit of 1.0 ppt NDMA in water. Comparative data between the Ambersorb 572 method and liquid-liquid extraction showed excellent agreement (average difference of 12 %). With the Ambersorb 572 method, dichloromethane use has been reduced by a factor of 1,000 and productivity has been increased by a factor of 3 - 4. Monitoring of a drinking water supply showed rapidly changing concentrations of NDMA from day to day.
Key words: NDMA; extraction method, rapid, solid-phase; Ambersorb 572
1
Introduction
N-nitrosodimethylamine (NDMA), Chemical Abstracts Service Registry Number [62-75-9], is a known carcinogen [1 - 3]. Tbe presence of NDMA is associated with many different industrial processes. It has been measured in air samples taken at tire factories and tanneries [4] and at metalworking factories [5]. NDMA is often found in food products such as beer [6] and cured meats [7, 8], and tobacco smoke [9]. NDMA has also been found in drinking water [ 1 0 - 13], surface water [14], and sea water [15]. NDMA may also be formed, under acidic conditions, by the reaction of amines with nitrites. As a result of finding NDMA in a drinking water supply in 1989 [16], the Ministry of Environment and Energy (MOEE) established a drinking water guideline of 9 ppt [18] and a regulatory limit of 200 ppt for effluents. To handle the workload resulting from monitoring NDMA for exceedences of the drinking water guideline and the
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 207-210 (1995) 9 ecomed publishers, D-86899 Landsberg, Germany
regulatory level for effluents, a new sample preparation method had to be developed. Previously, liquid-liquid extraction, the most common extraction method for removing NDMA from liquid matrices, was used [10, 14, 17, 19]. Some methods of NDMA analysis have used solid phase extraction (SPE) with various adsorbents including Amberlite XAD-2 resin [11], Ambersorb XE-340 [12], and other carbonaceous materials [10, 13, 15]. In this laboratory, a method of extraction was developed based on a granular adsorbent, Ambersorb 572. Ambersorb 572 consists of carbonaceous black, spherical beads that are produced by the pyrolysis of highly sulfonated styrene-divinyl benzene macroreticular ion exchange resin [20]. Initial experiments were performed with Carboxen 564 which was found to be an effective extraction agent. However, because Ambersorb 572 provided comparable NDMA extraction efficiencies and was less expensive than Carboxen 564, a method based on the use of Ambersorb 572 was developed. To simplify solid phase extraction, Ambersorb 572 was added directly to the water samples spiked with the internal standard ds-NDMA. The sample bottles were placed on a roller apparatus for the extraction. The Ambersorb 572, to which NDMA was adsorbed, was isolated by filtration, airdried and transferred to an autosampler vial. Dichloromethane was added to the vial, which was then capped and loaded onto the autosampler tray. The extract was analyzed on a gas chromatograph/high resolution mass spectrometer at a mass resolution of 7,000. To our knowledge, this paper presents the first method in which Ambersorb 572 is added directly to a water sample to effect NDMA extraction.
2
2.1
Experimental
Instrumentation, apparatus and reagents
Instrumentation: The instrumentation has been described in detail elsewhere [21] and is summarized here. A HewlettPackard 5890 Series II gas chromatograph (Hewlett-Packard, 207
NDMA in Drinking Water
Mississauga, Ontario, Canada) was equipped with a split/ splitless injector and a CTC A200S autosampler (Leap Technologies, Chapel Hill, North Carolina, USA). Chromatography was performed with a 30 m x 0.25 mm id, 1/lm film thickness, DB-1701 (J&W Scientific, Folsom, California, USA) column. A VG Analytical ZAB-2F doublefocusing reverse geometry magnetic sector mass spectrometer equipped with a DEC VAXstation 3100 (M76) and VG OPUS2000 (v2.1) software (Fisons, Manchester, UK) was operated in the electron ionization, single ion monitoring mode at 7,000 resolution (10 % valley). Apparatus: A roller apparatus that accommodated 1 L bottles (Hotpack Corporation, Philadelphia, Pennsylvania, USA) was modified with a variable speed control to achieve 50 rpm (Leeson Electric Corporation, Grafton, Wisconsin, USA). Reagents: Ambersorb 572 (Supelco Canada Ltd., Oakville, Ontario, Canada) was conditioned at 320 ~ for 3 hours before use. High purity water was obtained from a reverse osmosis/ion exchange/UV system (Biolab Equipment Canada Ltd., Oakville, Ontario, Canada). 2.2
Ambersorb 572 extraction
A 500 mL aliquot of the sample was transferred to a clean 1 L amber bottle with a Teflon-lined cap. After the addition of the internal standard, d6-NDMA , (15 ppt) and 200 mg of Ambersorb 572 (400/~L, measured in a flatbottom autosampler vial insert), the bottle was rolled at 50 rpm for 1 hour. The contents of the bottle were filtered through filter paper to collect the Ambersorb 572. The filter paper (with the Ambersorb 572) was transferred with forceps to a disposable aluminium dish, where it was allowed to air dry for 3 0 - 6 0 minutes. The dried Ambersorb 572 was transferred to an autosampler vial and 400/IL of dichloromethane were added. The vial was capped with a Teflon-lined crimp cap, tapped to expel air bubbles from the Ambersorb 572, and then loaded onto the autosampler tray for analysis. Procedure blanks were prepared in triplicate by adding d6-NDMA (15 ppt) and 200 mg Ambersorb 572 to 500 mL aliquots of high purity water. The average of the three blanks was used for the blank correction. Spiked control samples were prepared by adding NDMA (10.0 ppt and 200 ppt) to successive 500 mL aliquots of high purity water. To the first bottle were added d6-NDMA (15.0 ppt) and 200 mg Ambersorb 572. To the second bottle were added d6-NDMA (500 ppt) and 200 mg Ambersorb 572. A greater quantity of internal standard was added to adhere to the practice of spiking samples which are expected to contain high NDMA concentrations (ie. effluent samples) with comparable concentrations of internal standard. Additional control samples spiked at 5 ppt, 20 ppt, 40 ppt and 80 ppt NDMA were run with d6-NDMA at 15 ppt.
2.3
Liquid-liquid extraction
Liquid-liquid extraction was performed according to a Ministry of Environment and Energy standard procedure [17]. An 800 mL sample aliquot was transferred to a 1 L separatory funnel and spiked with d6-NDMA (15.8 ppt).
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Research Articles
The sample's pH was adjusted to 12 with a 50 % sodium hydroxide solution and the solution was serially extracted with dichloromethane. The combined dichloromethane extract was washed with a pH 2 sulphuric acid solution. The washed extract was filtered through granular anhydrous sodium sulphate and then concentrated by rotary evaporator and a nitrogen evaporating unit to approximately 200/IL.
2.4
Instrumental analysis
The detailed procedure has been described elsewhere [21]. The mass spectrometer was tuned to 7,000 resolution with perfluorotributylamine (PFTBA). Solutions of standards having NDMA and d6-NDMA concentrations ranging from 0.50 to 16440 pg injected and 1,3-diethylbenzene (1,3-DEB)(42 pg injected) were transferred to 200/aL conical inserts in the 2 mL autosampler vials which were then capped and loaded onto the autosampler tray. Multi-point calibration curves were generated in 3 segments. All standards contained a fixed amount of 1,3-DEB (42 pg injected) to correct for variability in the instrument sensitivity. NDMA concentrations in the procedure blanks, spiked control samples and samples were calculated by isotope dilution with d6-NDMA. M1 NDMA concentrations in the spiked control samples were corrected for the average NDMA concentration in the three procedure blanks.
3
Results and Discussion
In developing a new method for NDMA analysis, the goals were to increase lab productivity, minimize solvent use, glassware and reagents, number of steps, lower the cost of sample preparation and improve method precision, accuracy and detection limits. The Ambersorb 572 method successfully met all of these goals. It requires only 400/aL of dichloromethane per extraction. By comparison, the liquidliquid extraction method requires 300 mL (including glassware rinses) of dichloromethane per sample. Sodium sulphate, sodium hydroxide, sulphuric acid, separatory funnels, conical funnels and round bottom flasks are not required. The granular nature of the Ambersorb 572 facilitates isolation on filter paper and prevents the autosampler syringe from being plugged. Productivity has been increased to approximately 3 0 - 4 0 samples (including up to 12 QC samples) per person per day. This is a 3- to 4-fold increase with respect to liquid-liquid extraction. Extraction conditions. The mixing speed for the roller apparatus was set at 50 rpm to provide sufficient agitation for the Ambersorb 572 in the bottle and was not investigated further. The 200 mg of Ambersorb 572 were chosen because this amount was easily measured in a vial insert as 400/aL and this amount was compatible with 400/~L dichloromethane in a 2 mL autosampler vial. Using a 500 mL sample size afforded the opportunity to perform replicate analyses on a 1 L water sample.
Extraction time. Figure 1 shows a plot of NDMA and d6-NDMA recovered from 17 water samples (spiked with 40.5 ppt NDMA and 25.1 ppt d6-NDMA) versus minutes rolled with Ambersorb 572. The amount of analyte extracted
E S P R - E n v i r o n . Sci. & Pollut. Res. 2 (4) 1995
Research Articles
N D M A in Drinking Water
by the Ambersorb 572 gradually increased over a period of approximately 50 minutes and then reached equilibrium. However, an equilibrium between the analyte in the water and analyte adsorbed to Ambersorb 572 is not a requirement for accurate quantitation with isotope dilution. EXTRACTION TIME STUDY
0
100
50
150
MINUTES
200
250
ROLLED
I+ ~ N
d6-NDMA
I
2o
o
0
so
,;,~uTEs.od~ ~
~oo
Fig. 1: Plots of NDMA and d6-NDMA recovered from spiked water samples versus minutes rolled with Ambersorb 572. The total amounts of NDMA and d6-NDMA in each 500 mL high purity water sample were 20.3 ng (40.5 ppt) and 12.6 ng (25.1 ppt) respectively. Each point represents a single measurement
relative standard deviations were less than 4 %. Day-to-day precision and accuracy were assessed by averaging all 32 measurements collected during the study period. Measured concentrations and relative standard deviations for the low and high N D M A spikes were 9.63 ppt and 4.2 % and 198 ppt and 3 . 1 % , respectively. Method detection limits and recoveries. Method detection limits and recoveries were also determined by analyzing eight replicate samples (spiked with 10.0 ppt NDMA) per day on four days. The highest method detection limit, defined as three times the standard deviation of replicate measurements [22], calculated for the four day period was 1.0 ppt. This was better than the 1.6 ppt detection limit obtained with the liquid-liquid extraction method [17]. Using data from the above experiments (10.0 ppt NDMA), the within-run average recoveries for N D M A and d6-NDMA were determined to be the same at the 95 % confidence level. Betweenrun recoveries ranged from 26 % to 4 1 % . By comparison, recoveries of N D M A by liquid-liquid extraction have been 20 - 30 % for most samples. This low recovery can be advantageous. Table 1 shows the data generated by serial extractions of 3 water samples spiked with 10.0 ppt NDMA. The average recovery in each extraction was approximately 40 %. The total recovery for the 4 extractions was 89 %. The concentrations of N D M A are the same in all of the extractions. Thus, with the Ambersorb 572 method, it is possible to obtain up to 4 replicate analyses with the same sample. Table 1: Serial extraction of water samples with Ambersorb 572
Figure 2 shows the concentrations of N D M A measured using various extraction times. The concentration of N D M A measured in each sample was independent of the extraction time. Thus, an extraction time of 60 minutes was chosen because it yielded the maximum NDMA recovery in the least amount of time. At 60 minutes, both N D M A and d6-NDMA recoveries were 40 %.
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o"
c
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2
5
10
13
16
2O
30
4O
50
8O
~
105
120
150
180
210
Extraction/Rolling Time (minutes)
Fig. 2: Measured NDMA concentrations at varying extraction times. A 500 mL high purity water sample was spiked with 20.3 ng (40.5 ppt) of NDMA and 12.6 ng (25.1 ppt) of d6-NDMA Method precision and accuracy. The method's within day precision and accuracy were determined by analyzing eight replicate samples of high purity water (spiked with 10.0 ppt NDMA) and another eight samples (spiked with 200 ppt NDMA) per day on four days. The daily average N D M A concentrations were within 6 % of the expected values and
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995
Actual NDMA Measured Measured Measured Measured Concentration (pptl NDMA (ppt) NDMA (ppt) NDMA (ppt) NDMA (ppt) Extraction #1 Extraction #2 Extraction 03 Extraction 10.0
9.11+1.0%
9.37+5.2%
9.14___7.1%
Recovery
40 %
24 %
15 %
8.83• 10 %
Comparative studies. The results of 39 pairs of analyses in which drinking and surface waters were extracted by both the Ambersorb 572 method and by liquid-liquid extraction with dichloromethane were compared. A plot of the log of NDMA concentrations measured by the Ambersorb 572 method versus the log of NDMA concentrations measured by liquidliquid extraction is shown in Figure 3. The correlation coefficient (r) is 0.98, indicating that N D M A concentrations measured using Ambersorb 572 extraction and those measured using liquid-liquid extraction are significantly related. The slope of the regression line for this plot is 1.02, which suggests that the N D M A concentrations obtained by the Ambersorb 572 method are comparable to those obtained by liquid-liquid extraction. The differences in concentrations averaged 12 %. Monitoring studies. In 1989, N D M A was found in an Ontario drinking water sample which was collected as part of the province's Drinking Water Surveillance Program [16]. As a consequence of finding elevated levels of N D M A in a series of samples from one location, the ministry set an interim-guideline of 14 ppt in drinking water and a regulatory
209
N D M A in Drinking Water
Research Articles
level of 500 ppt in effluents. In 1990, the ministry revised the drinking water guideline to 9 ppt [18]. In 1992, the regulatory level for effluents was revised to 200 ppt.
Acknowledgements The authors would like to thank Dr. Bill BERGfor the donation of the roller apparatus and Patrick RILEY and Walter OFFENBACHERfor performing the necessary modifications to it. The authors would also like to thank Dr. Ray CLEMENTfor helpful suggestions.
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5
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8
9 9~ 0"5R5
9 R9r" "-%
1
13
2
LogNDMAConccntral~o~by Laquid- L/quidExlraclion(ppl)
2.$
Fig. 3: Plot of the logarithms of NDMA concentrations determined by the Ambersorb method versus the liquid-liquid extraction for 39 samples. The correlation coefficient r is 0.98 and the slope of the regression line is 1.02
Table 2 shows the results of replicate analyses of raw and treated water from a drinking water supply. Concentrations less than the reporting limit (RL) of 5 ppt are listed as not detected [ND (RL)]. These data show that, if the precursors to NDMA are present in the raw water, the treatment process generates NDMA. The data also demonstrate that the concentrations of NDMA can change rapidly from day to day. At the time that NDMA was detected at this location, sampling was being done weekly. Bi-weekly or monthly sampling might have been insufficient to detect NDMA. Therefore, at some locations, there are requirements to sample frequently and to have the capacity to handle a large number of samples once NDMA is detected. Table 2: N D M A Concentrations in a Drinking Water Supply
Date Sampled (Day)
Raw Water (ppt)
Treated Water (ppt)
Jan. 3 (1)
ND (5), ND (5)
ND (5), ND (5)
,Jan. 10 (8)
ND (5), ND (5)
90, 92
Jan. 14 (12)
7, 8
150, 150
Jan. 15 (13)
18, 17
180, 180
Jan. 16 (14)
ND (5), ND (5)
28, 32
Jan. 17 (15)
ND (5), ND (5)
ND (5), ND (5)
4
Conclusions
The performance data and comparative studies have allowed this laboratory to replace the liquid-liquid extraction method with the Ambersorb 572 method in the analysis of NDMA from water. The increase in productivity is a factor of 3 - 4 even though there has been a 6-fold increase in the number of QC samples per batch of samples. The new methodology described in this paper has increased the sample capacity of this laboratory and has allowed frequent monitoring of drinking water supplies should concentrations of NDMA exceed the drinking water guideline or the effluent regulatory limit.
210
References
[1] FREUND, H. A.: Clinical Manifestations and Studies in Parenchymatous Hepatitis. Ann. Intern. Med. 10, 1144 (1937) [2] MAGEE,P. N.; J. M. BARNES:Carcinogenic Nitroso Compounds. Advanc. Cancer Res. 10, 163 (1967) [3] IARC Monograph on the Evaluation of Carcinogenic Risk of Chemicals to Man. 1, 85 (1972) [4] FINE, D. H.; D. P. ROUNBEHLER:Occurrence of N-Nitrosamines in the Workplace. In: R.A. SCANLAN;S. R. TANNENBAUM,(Eds.), ACS Symposium Series, No. 174: N-Nitroso Compounds, Amer. Chem. Soc., 1981, p. 207 [5] FADLALLAH,S.; S. F. COOPER; M. FOURNIER;D. DROLET;G. PERRAULT: Determination of N-nitroso Compounds in the Environment of a Metal Factory Using Metalworking Fluids. Int. J. Environ. Anal. Chem. 39, 281 (1990) [6] S E N , N . P . ; S. S E A M A N : Gas-Liquid Chromatographic-Thermal Energy Analyzer Determination of N-Nitrosodimethylamine in Beer at Low Parts per Billion Level. J. Assoc. Off. Anal. Chem. 64, 933 (1981) [7] HAVERY,D. C.; T. FAZ10;J. W. HOWARD:Survey of Cured Meat Products for Volatile N-Nitrosamines: Comparison of Two Analytical Methods. J. Assoc. Off. Anal. Chem. 61, 1374 (1978) [8] HOTCHKISS,J. H.; L. M. LJBBEY;J. F. BARBOUR;R. A. SCANLAN: Combination of a GC-TEA and a GC-MS-Data System for tbe /~g/kg Estimation and Confirmation of Volatile N-Nitrosamines in Foods. IRAC Sci. Publ. 10, 361 (1980) [9] DRUCKREY,H.; R. PREUSSMANN:Zur Entstehung carcinogener Nitrosamine am Beispiel des Tabakrauchs. Naturwiss. 49, 498 (1962) [10] FINE, D. H.; D. P. ROUNBEHLER;F. HUFFMAN;A. W. GARRISON; N. L. WOLFE;S. S. EPSTEIN:Analysis of Volatile N-Nitroso Compounds in Drinking Water at the Part per Trillion Level. Bull. Environ. Contam. Toxicol. 14, 404 (1975) [11] NIKAIDO,M. M.; D. DEAN-RAYMOND;A. J. FRANCIS;M. ALEXANDER: Recovery of Nitrosamines from Water. Water Res. 11, 1085 (1977) [12] KIMOTO, W . I . ; C . J . DOOLEY; J. CARRfl; W. FIDDLER: Nitrosamines in Tap Water After Concentration by a Carbonaceous Adsorbent. Water Res. 15, 1099 (1981) [13] KUL'BICH,T. S.; L. A. TIKTIN; A. A. GLAVIN: Sorptive Concentration as a Method for Improving Sensitivity of Determination of Nitrosamines in Water. J. Anal. Chem. USSR. 44, 1289 (1989) [14] FINE, D . H . ; D.P. ROUNBEHLER: N-Nitroso Compounds in Water. In: L . H . KEITH (Ed.), Identification & Analysis of Organic Pollutants in Water, Ann Arbor Science Publ. Inc, Ann Arbor, Michigan 1976, p. 255 [15] KADOKAMI,K.: Trace Analysis of Water-Soluble Compounds Using Activated Carbon Extraction Method. PPM. 22, 37 (1991) [16] Ministry of Environment and Energy (MOEE): Scientific Criteria Document for Multimedia Standard Development No. 01 - 90: N-Nitrosodimethylamine, ISBN 07729-8318-6. March (1991) [17] Ministry of Environment and Energy: The Determination of NNitrosodimethylamine (NDMA) in drinking Water and in Aqueous Samples by Gas Chromatography/High Resolution Mass Spectrometry, LSB Method MSABN-E3291A. (1993) [18] Ministry of Environment and Energy: Ontario Drinking Water Objectives, 5th Edition. (1994) [19] Method 607-Nitrosamines. (EPA) Federal Register: 49, 81 (1984) [20] Supelco, Inc: Ambersorb 572 Data Sheet (DS710085). (1990) [21] TAGUCHI, V. Y.; S. W., D. JENKINS; D. T. WANG; J.-P. F. P. PALMENTIER; E . J . REINER: The Determination of Nnitrosodimethylamine by Isotope Dilution High Resolution Mass Spectrometry. Can. J. Appl. Spectrosc. 39, 878 (1994) [22] TAYLOR,J. K: Quality Assurance of Chemical Measurements. Lewis Publishers, Inc. Chelsea, Michigan 1987 Received: April 18, 1995 Accepted: August 22, 1995
ESPR-Environ. Sci. & Pollut. Res. 2 (4) 1995
