1,4-Dioxane is used as a solvent for a variety of practical applications as well as in the laboratory1-4 and a contaminant of some ingredients used in the manufacture of personal care products and cosmetics.5 Acute (short-term) inhalation exposure to high levels of 1,4-dioxane has caused vertigo, drowsiness, headache, anorexia and irritation of the eyes, nose, throat, and lungs in humans.6 It may also irritate the skin.6 Damage to the liver and kidneys has been observed in rats chronically (long-term) exposed in their drinking water. In three epidemiologic studies on workers exposed to 1,4-dioxane, the observed number of cancer cases did not differ from the expected cancer deaths. Tumors have been observed in orally exposed animals
The International Agency for Research on Cancer classified 1,4-dioxane as a Group 2B carcinogen : possibly carcinogenic to humans because it is a known carcinogen in other animals7 and the U.S. environmental protection agency (US EPA) classified it as a probable human carcinogen.8 World Health Organization suggested 50 μg/L as the maximum contaminant level.9 1,4-Dioxane is often found in many water sources: industrial waste water, stream water and ground water. The monitoring is required to establish new water quality criteria.
A wide range of analytical techniques has been developed to monitor the contaminant at trace levels in environmental samples. Most of these procedures are based on determining 1,4-dioxane by using a gas chromatography-flame ionization detector (GC-FID)10-12 and gas chromatography-mass spectrometry (GCMS). 13-19 Recently, a specific and highly sensitive headspace solid phase microextraction (SPME) 20-23 and a isotopic dilution headspace (IDHS)24 GC-MS were developed for the determination of 1,4-dioxane in water.
The aim of this paper was to measure trace 1,4-dioxane in surface water using IDHS GC-MS and to provide basic data to establish new surface water quality criteria.
2.1. Chemicals and reagents
1,4-Dioxane, 1,4-dioxane-d8, sodium chloride, acetone and methanol were purchased from Sigma- Aldrich (St. Louis, MO, USA). Water was purified by milli-Q equipment (Millipore Corp., Milford, MA, USA).
2.2. Water sampling and extraction procedure
Surface water samples were collected from 16 basins in the Gum River without headspace in 40 mL VOC bottles containing 1 drop of 2 M HCl. The sampling sites were selected to uniformly represent all streams of the River. All samples were collected in duplicate, and 5 mL water were placed in a 10 mL headspace vial containing 2 g NaCl. 50 μL of 1,4- dioxane-d8 solution (1.0 mg/L in milli-Q water) as an internal standard was added in the sample as soon as possible, and then the vial was sealed with a cap. The sample vial was placed in a heating block for 30 min at 90 ℃.
2.3. Gas chromatography-mass spectrometry
An Agilent 6890/5973 N instrument and a Combipal Autosampler (Agilent, USA), which allows automated HS injections, were used. All mass spectra were obtained with an Agilent 6891/5973N instrument. The ion source was operated in the electron ionization mode (EI; 70 eV, 230 ℃) and full-scan mass spectra (m/z 40-800) were recorded for analyte identification. An HP-InnoWax capillary column (40 m × 0.25 mm I.D. × 0.25 μm film thickness) was used. Samples were injected in the splitless mode. The flow rate of helium as a carrier gas was 1.0 mL/min. The injector temperature was set at 210 ℃. The oven temperature programs were as follows: an initial temperature of 35 ℃ (held for 3 min) increased to the final temperature of 220 ℃ at 8 ℃/min. Head space conditions of 1,4-dioxane are as described in Table 1. The ions selected by SIM were m/z 88, 58 and 57 for 1,4-dioxane and m/z 96, 64 and 62 for 1,4-dioxane-d8 (internal standard).
Table 1.Head space conditions of 1,4-dioxane
2.4. Calibration and quantification
Calibration curves for 1,4-dioxane were established by extraction after adding 0.5, 2.0, 5.0, 20, 50, 100 and 250 ng of the standard and 50 ng of the internal standard (1,4-dioxane-d8) to 5.0 mL of water. The ratios of the peak area of the standard to that of the internal standard were used in the quantification of the compounds.
3. Results and Discussion
3.1. Method validation
For the GC separation of 1,4-dioxane, the use of the semi-polar stationary phase was found to be efficient. Chromatograms are shown in Fig. 1. As can be seen from the figure, the peaks of 1,4-dioxane and the internal standard are symmetrical and separation of the analytes from the background compounds in the water samples was good. The retention time of 1,4-dioxane was 8.19 min. There were no extraneous peaks observed in a chromatogram of spiked water in the near of the retention time of 1,4-dioxane.
Fig. 1.GC-MS chromatogram from (a) a spiked ultra-pure water sample at 10 μg/L and a river water sample (1,4- dioxane was detected in concentration of 0.1 μg/L (b) and 1,4-dioxane-d8 was spiked at 10.0 μg/L (c)).
The method was validated for linearity, the limit of detection (LOD), the limit of quantification (LOQ), precision and accuracy.
Calibration curves of the 1,4-dioxane were constructed by extraction of the spiked water samples. Examination of the typical standard curve by computing a regression line of peak area ratios for the 1,4- dioxane to the internal standard on concentrations using a least-squares fit demonstrated a linear relationship with correlation coefficients of 0.9997. The line of best fit for 1,4-dioxane is y = 0.0952x + 0.0134 over a range of 0.1-50 μg/L, where x is the analyte concentration (μg/L) and y is the peak area ratio of the analyte to the internal standard.
We have defined and calculated as following: LOD and LOQ were defined by 3.14 and 10 times the standard deviation for replicate determinations (n=7) from samples spiked at the concentration of 0.01 μg/L in stream water, in which the analyte was not detected. The LOD in this study was 0.02 μg/L and the LOQ was 0.07 μg/L using a 5.0 mL sample.
The accuracy can be assessed by determining the recovery in spiked samples: Intra-day accuracy was evaluated using five spiked samples at concentrations of 10.0 and 50.0 μg/L for 1,4-dioxane. The inter-day accuracy was determined using sample recovery on three different days. The accuracy was in the range of approximately 96 to 99%, and the precision of the assay was less than 6%, as shown in Table 2.
Table 2.Intraday and interday laboratory precision and accuracy results for the analysis of 1,4-dioxane in water (n=5)
3.2. Water analysis
We analyzed the target compound in 44 surface water samples. 1,4-Dioxane was detected in a concentration range of 0.49-43.0 μg/L in 13 samples of the 44 surface water samples collected from Gum-River, Korea. In 1st survey (in June, 2012), 1,4- dioxane was detected in a concentration range of 0.61-43.0 μg/L (mean=2.2 μg/L) in 3 samples of the 22 surface water samples. Otherwise, in 2nd survey (in September, 2012), 1,4-dioxane was detected in a concentration range of 0.49-7.8 μg/L (mean=1.7 μg/ L) in 10 samples of the 22 surface water samples.
We measured the target compound in 44 surface water samples. 1,4-Dioxane was detected in a concentration range of 0.49-43.0 μg/L in 13 samples of the 44 surface water samples collected from Gum- River. Maximum concentration of 1,4-dioxane detected in surface showed lower than Korea drinking water guideline.25 The concentrations of 1,4-dioxane in environmental water were comparable to those present in other countries. 1,4-dioxane at the level of 1 μg/L has been detected in many locations in the US. In the state of New Hampshire alone in 2010 it had been found at 67 sites, ranging in concentration from 2 μg/L to over 11,000 μg/L.26 Although the production of 1,4-dioxane in Korea is decreasing, its existence in river water calls for identifying its origin. 1,4-Dioxane can be discharged as a by-product in the industry of stabilizer, inks and adhesives.