METHOD 9022
TOTAL ORGANIC HALIDES (TOX) BY NEUTRON ACTIVATION ANALYSIS
1.0SCOPE AND APPLICATION
1.1Method 9022 determines Total Organic Halides (TOX) in aqueous samples. The method us a carbon adsorption procedure identical to that of Method 9020 (TOX analysis using a microcoulometric-titration detector), irradiation by neutron bombardment, and then detection using a gamma-ray detector.
1.2Method 9022 detects all organic halides containing chlorine, bromine, and iodine that are adsorbed by granular activated carbon under the conditions of the method. Each halogen can be quantitated independently.
1.3Method 9022 is restricted to u by, or under the supervision of, analysts experienced in the operation of neutron activation analysis and familiar with spectral interferences.
1.4This method, which may be ud in place of Method 9020, has the advantage of dete左半边翅膀
rmining the individual concentrations of the halogens chlorine, bromine, and iodine in addition to TOX.
2.0SUMMARY OF METHOD
2.1 A sample of water that has been protected against the loss of volatiles by the elimination of headspace in the sampling container, and that is free of undissolved solids, is pasd through a column containing 40 mg of granular activated car臀部按摩手法
bon (GAC). The column is washed to remove any trapped inorganic halides. The GAC sample is expod to thermal neutron bombardment, creating a radioactive isotope. Gamma-ray emission, which is unique to each halogen, is counted. The areas of the resulting peaks are directly proportional to the concentrations of the halogens.
3.0INTERFERENCES
3.1Method interferences ma酿酒坊
y be caud by contaminants, reagents, glassware, and other sample processing hardware. All the materials must be routinely demonstrated to be free from interferences under the conditions of the analysis by running method blanks.
3.1.1 Glassware must be scrupulously cleaned. Clean all glassware
as soon as possible after u by treating with chromatic cleaning solution. This should be followed by detergent washing in hot water.
Rin with tap water and distilled water and drain dry; glassware which is not volumetric should, 抽噎造句
in addition, be heated in a muffle furnace at
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400E C for 15 to 30 min. Volumetric ware should not be heated in a muffle furnace. Glassware should be aled and stored in a clean environment after drying and cooling to prevent any accumulation of dust or other contaminants.
3.1.2The u of high-purity reagents and gas helps to minimize
interference problems.
3.2Purity of the activated carbon must be verified before u. Only carbon samples that register less than 2,000 ng Cl /40 mg GAC should be ud.-The stock of activated carbon should be 工作表现评语
stored in its granular form in a glass container with a Teflon al. Exposure to the air must be minimized, especially during and after milling and sieving the activated carbon. No mo俄罗斯教育
re than a 2-wk supply should be prepared in advance. Protect carbon at all times from all sources of halogenated organic vapors. Store prepared carbon and packed columns in glass containers with Teflon als.
4.0APPARATUS AND MATERIALS
4.1Adsorption system (a general schematic of the adsorption system is sho学美术的好处
wn in Figure 1):
4.1.1
Adsorption module with pressurized sample and nitrate-wash rervoirs.
4.1.2Adsorption columns : Pyrex, 5-cm long x 6-mm O.D. x 2-mm I.D.
4.1.3Granular activated carbon (GAC): Filtrasorb-400, Calgon-APC
or equivalent, ground or milled, and screened to a 100/200 mesh range. Upon combustion of 40 mg of GAC, the apparent halide background should be 1000ng C1 equivalent or less.
-4.1.4Cerafelt (available from Johns-Manville) or equivalent: Form
this material into plugs using a 2-mm-I.D. stainless steel borer with ejection rod to hold 40 mg of GAC in the adsorption columns.
CAUTION: Do not tou借款利率计算
ch this material with your fingers. Oily
residue will contaminate carbon.
4.1.5
Column holders .4.1.6Volumetric flasks : 100-mL, 50-mL.
4.2Containers suitable for containment of samples and standards during irradiation (e.g., 1/5-dram polyethylene snap-cap vial).
4.3Sample introduction system and a reactor generating a thermal neutron flux capable of achieving enough halogen activity for counting purpos (e.g.,a reactor having a neutron flux of 5 x 10 neutrons/cm /c).
1224.4 A gamma-ray detector and data-handling system capable of resolving the halogen peaks from potential interferences and background.
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5.0REAGENTS
5.1Prepurified nitrogen.
5.2ASTM Type II water (ASTM D1193): Water should be monitored for impurities.
5.3Nitrate-wash solution (5,000 mg NO /L): Prepare a nitrate-wash 3-solution by transferring approximately 8.2 g of potassium nitrate (KNO ) into a 31-liter volumetric flask and diluting to volume with Type II water.
5.4Acetone and nanograde hexane (50% v/v mixture).5.5Sodium sulfite, 0.1 M (ACS reagent grade,
12.6 g/L).5.6妇女节活动策划
Concentrated nitric acid (HNO ): Reagent grade.35.7Standards: 25-ug C1, 2.5-ug Br, and 2.5-ug I.5.8Radioactive standards to be ud for calibrating gamma-ray detection
systems.5.9Trichlorophenol solution, stock (1 uL = 10 ug C1): Prepare a stock -solution by accurately weighing accurately 1.856 g of trichlorophenol into a 100-mL volumetric flask. Dilute to volume with methanol.
5.10Trichlorophenol standard, adsorption efficiency (100 ug C1/liter):-Prepare an adsorption-efficiency standard by injecting 10 uL of stock solution into 1 liter of Type II water.
6.0SAMPLE COLLECTION, PRESERVATION, AND HANDLING
6.1All samples must have been collected using a sampling plan that address the considerations discusd in Chapter Nine of this manual.
6.2All samples should be collected in bottles with Teflon pta (e.g.,Pierce #12722 or equivalent) and be protected from light. If this is not possible, u amber glass, 250-mL, fitted with Teflon-lined caps. Foil may be substituted for Teflon if the sample is not corrosive. Samples must be protected against loss of volatiles by eliminating headspace in the container. Containers must be washed and muffled at 400E C before u, to minimize contamination.
6.3All glassware must be dried prior to u according to the method discusd in Paragraph 3.1.1.
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7.1Sample preparation:
7.1.1Special care should be taken in handling the sample in order
to minimize the loss of volatile organohalides. The adsorption procedure should be performed simultaneously on the front and back columns.
7.1.2Reduce residual chlorine by adding sulfite (1 mL of 0.1 M
sulfite per liter of sample). Sulfite should be added at the time of sampling if the analysis is meant to determine the TOX concentration at the time of sampling. It should be recognized that TOX may increa on storage of the sample. Samples should be stored at 4E C without headspace.
7.1.3Samples containing undissolved solids should be centrifuged
and decanted.
7.1.4Adjust the pH of the sample to approximately 2 with
concentrated HNO just prior to adding the sample to the rervoir.
37.2Calibration:
7.2.1Check the adsorption efficiency of each newly prepared batch
of carbon by analyzing 100 mL of the adsorption efficiency standard, in duplicate, along with duplicates of the blank standard. The net recovery should be within 5% of the standard value.
7.2.2Nitrate-wash blanks (method blanks): Establish the
repeatability of the method background each day by first analyzing veral nitrate-wash blanks. Monitor this background by spacing nitrate-wash blanks between each group of eight analysis determinations. The nitrate-wash blank values are obtained on single columns packed with 40 mg of activated carbon.Wash with the nitrate solution, as instructed for sample analysis, and then analyze the carbon.
7.2.3Prior to each day's operation, calibrate the instrument using
radioactive standards (e.g., cobalt-60 and radium-226 sources). The instrument is calibrated such that gamma rays from the standards fall within one channel of their true energies. A 100-c blank is then counted to verify that no stray radioactive sources are within nsing distance of the detector. As data are obtained throughout the day, peak locations in the standards are monitored to ensure there is no electronic drift of the instrument. If drift is noted, the system must be recalibrated.
7.3Adsorption procedure:
7.3.1Connect in ries two columns, each containing 40 mg of
100/200-mesh activated carbon.
