METHOD 8032A
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ACRYLAMIDE BY GAS CHROMATOGRAPHY
1.0SCOPE AND APPLICATION
1.1Method 8032 is ud to determine trace amounts of acrylamide monomer (CAS No. 79-06-1) in aqueous matrices. This method may be applicable to other matrices and to other similar analytes.
1.2The method detection limit (MDL) in an aqueous matrix is 0.032 µg/L.
1.3This method is restricted for u by, or under the supervision of, analysts experienced in the u of gas chromatographs and skilled in the interpretation of gas chromatograms. Each analyst must demonstrate the ability to generate acceptable results with this method.
2.0SUMMARY OF METHOD
2.1Method 8032 is bad on bromination of the acrylamide double bond. The reaction product (2,3-dibromopropionamide) is extracted from the reaction mixture with ethyl acetate, after salting out with sodium sulfate. The extract is cleaned up using a Florisil column, and analyzed by gas chromatography with electron capture detection (GC/ECD).
2.2Compound identification should be supported by at least one additional qualitative technique. Analysis using a cond gas chromatographic column or gas chromatography/mass spectrometry may be ud for compound confirmation.
留学生购车免税政策3.0INTERFERENCES
3.1No interference is obrved from awater or in the prence of 8.0% of ammonium ions derived from ammonium bromide.
3.2Impurities from potassium bromide are removed by the Florisil cleanup procedure.
4.0APPARATUS AND MATERIALS
4.1Gas chromatographic system
4.1.1Gas chromatograph suitable for on-column injections with all required
accessories, including detector, analytical columns, recorder, gas, and syringes. A data system for measuring peak heights and/or peak areas is recommended.
4.1.2GC Column - 2 m x 3 mm glass column, 5% FFAP (free fatty acid polyester) on
60-80 mesh acid washed Chromosorb W, or equivalent.
4.1.3Detector - electron capture detector.
4.2Separatory funnel - 150-mL.
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4.3Volumetric flask (Class A) - 100-mL, with ground-glass stopper; 25-mL, amber, with ground-glass stopper.
4.4
Syringe - 5-mL.4.5
Microsyringes - 5-µL, 100-µL.4.6
Pipets (Class A).4.7
Glass chromatography column (30 cm x 2 cm).4.8
Mechanical shaker.5.0REAGENTS
5.1Reagent grade chemicals shall be ud in all tests. Unless otherwi indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be ud, provided it is first ascertained that the reagent is of sufficiently high purity to permit its u without lesning the accuracy of the determination.
5.2Organic-free reagent water. All references to water in this method refer to organic-free reagent water, as defined in Chapter One.
5.3Solvents - All solvent must be pesticide quality, or equivalent.
5.3.1Ethyl acetate, C H CO C H 25225
5.3.2Diethyl ether, C H OC H . Must be free of peroxides as indicated by test strips
2525(EM Quant, or equivalent). Procedures for removal of peroxides are provided with the test strips. After cleanup, 20 mL of ethyl alcohol prervative must be added to each liter of ether.
5.3.3
Methanol, CH OH 35.3.4
Benzene, C H 665.3.5Acetone, CH COCH 33
5.4Saturated bromine water - Prepare by shaking organic-free reagent water with bromine and allowing to stand for 1 hour, in the dark, at 4E C. U the aqueous pha.
5.5Sodium sulfate (anhydrous, granular), Na SO . Purify this reagent by heating at 400E C 24for 4 hours in a shallow tray, or by precleaning the sodium sulfate with methylene chloride. If the sodium sulfate is precleaned with methylene chloride, a method blank must be analyzed,demonstrating that there is no interference from the sodium sulfate.
5.6
Sodium thiosulfate, Na S O , 1 M aqueous solution.2235.7
Potassium bromide, KBr, prepared for infrared analysis.5.8
Concentrated hydrobromic acid, HBr, specific gravity 1.48.
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5.9
Acrylamide monomer, H C:CHCONH , electrophoresis reagent grade, minimum 95%
22purity.5.10Dimethyl phthalate, C H (COOCH ), 99.0% purity.
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64325.11Florisil (60/100 mesh): Prepare Florisil by activating at 130E C for at least 16 hours.Alternatively, store Florisil in an oven at 130E C. Before u, cool the Florisil in a desiccator. Pack 5 g of the Florisil, suspended in benzene, in a glass column (Sec. 4.8).NOTE:Benzene is toxic, and should only be ud in a ventilated laboratory hood.
5.12Stock standard solution
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Prepare a stock standard solution of acrylamide monomer as described below. When
compound purity is assayed to be 96% or greater, the weight can be ud without correction to calculate the concentration of the stock standard. Commercially-prepared standards can be ud at any concentration if they are certified by the manufacturer or by an independent source.
Dissolve 105.3 mg of acrylamide monomer in organic-free reagent water in a 100-mL volumetric flask, and dilute to the mark with organic-free reagent water. Dilute the solution of acrylamide monomer so as to obtain standard solutions containing 0.1 - 10 mg/L of acrylamide monomer.
5.13Calibration standards
Dilute the acrylamide stock solution with organic-free reagent water to produce standard
solutions containing 0.1 - 5 mg/L of acrylamide. Prior to injection the calibration standards are reacted and extracted in the same manner as environmental samples (Sec. 7.0).
5.14Internal standards
The suggested internal standard is dimethyl phthalate. Prepare a solution containing 100
mg/L of dimethyl phthalate in ethyl acetate. The concentration of dimethyl phthalate in the sample extracts and calibration standards should be 4 mg/L.
6.0SAMPLE COLLECTION, PRESERVATION, AND HANDLING
6.1
See the introductory material to this chapter, Organic Analytes, Sec. 4.1.7.0PROCEDURE
7.1Bromination
7.1.1Pipet 50 mL of sample into a 100-mL glass-stoppered flask. Dissolve 7.5 g of
potassium bromide into the sample, with stirring.
7.1.2Adjust the pH of the solution with concentrated hydrobromic acid until the pH is
between 1 and 3.
7.1.3Wrap the flask with aluminum foil in order to exclude light. Add 2.5 mL of
saturated bromine water, with stirring. Store the flask and contents in the dark, at 0E C, for at least 1 hour.
7.1.4After reacting the solution for at least 1 hour, decompo the excess of bromine
by adding 1 M sodium thiosulfate solution, drop by drop, until the solution becomes colorless.
7.1.5Add 15 g of sodium sulfate and stir vigorously using a magnetic stirrer.
7.2Extraction
7.2.1Transfer the solution into a 150-mL paratory funnel. Rin the reaction flask
three times with 1-mL aliquots of organic-free reagent water. Transfer the rinsings into the paratory funnel.
7.2.2Extract the aqueous solution twice with 10-mL portions of ethyl acetate for 2 min
each extraction, using a mechanical shaker at approximately 240 strokes per minute. Dry the organic pha with 1 g of sodium sulfate.
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7.2.3Transfer the organic pha into a 25-mL amber volumetric flask. Rin the
mortalsodium sulfate with three 1.5-mL portions of ethyl acetate and combine the rinsings with the organic pha.
7.2.4Add exactly 100 µg of dimethyl phthalate to the flask and make the solution up
to the 25 mL mark with ethyl acetate. Inject a 5-µL aliquot of this solution into the gas chromatograph.
7.3Florisil cleanup - Whenever interferences are obrved, the samples should be cleaned up as follows.
7.3.1Transfer the dried extract into an evaporation vesl with 15 mL of benzene.
Evaporate the solvent at 70E C under reduced pressure, and concentrate the solution to about
3 mL.
7.3.2Add 50 mL of benzene and subject the solution to Florisil column chromatography
at a flow rate of 3 mL/min. Elute the column first with 50 mL of diethyl ether/benzene (1:4) at
a flow rate of 5 mL/min, and then with 25 mL of acetone/benzene (2:1) at a flow rate of 2
mL/min. Discard all of the first eluate and the initial 9 mL portion of the cond eluate, and u the remainder for the determination, using dimethyl phthalate (4 mg/L) as an internal standard.
NOTE:Benzene is toxic, and should be only be ud in a ventilated laboratory hood.
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7.4Gas chromatographic conditions
Nitrogen carrier gas flow rate:40 mL/min
Column temperature: 165E C.
Injector temperature: 180E C
Detector temperature: 185E C.
Injection volume: 5 µL
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Concentration (µg/L)'(A )(C )(D)(V )
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7.5Calibration
7.5.1Inject 5 µL of a method blank (organic-free reagent water carried through all
sample storage, handling, bromination and extraction procedures) into the GC.
7.5.2Prepare a minimum of five standard solutions of acrylamide as described in Sec.
5.13.1. One standard should be near the detection limit of the method. The remaining four standards should bracket the expected sample concentrations and cover the linear working range of the instrument. Brominate and extract each standard solution as described in Secs.
7.1 and 7.2.
7.5.3Inject 5 µL of each of the brominated and extracted standards, and record the instrument respon.
7.5.4Calculate the respon factor relative to the internal standard for each calibration
standard according to the guidance in Sec. 7.0 of Method 8000.
7.5.5Calculate the mean, standard deviation, and relative standard deviation of the respon factors from the five calibration standards, using the equations found in Sec. 7.0 of Method 8000.
7.5.6If the RSD of the respon factors is less than or equal to 20%, then the calibration can be assumed to be linear, and an average respon factor may be ud to calculate sample results. If the RSD is greater than 20%, e Method 8000 for alternative approaches to calibration.
7.6Sample analysis
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7.6.1Inject 5-µL portions of each sample extract (containing 4 mg/L internal standard)
into the gas chromatograph. An example GC/ECD chromatogram is shown in Figure 1.
7.6.2The concentration of acrylamide monomer in the sample is calculated according
to the following equation.
where:
不客气 英文A =Area (or height) of the peak for the analyte in the sample.x A =Area (or height) of the peak for the internal standard.is C =Concentration of the internal standard in the concentrated sample extract is
(µg/L). D
=Dilution factor, if the sample or extract was diluted prior to analysis. If no dilution was made, D = 1. The dilution factor is always dimensionless.V =Volume of the extract injected (µL). The injection volume for samples and i
calibration standards must be the same.RF
=Mean respon factor from the initial calibration. ––V =Volume of the aqueous sample extracted or purged (mL). If units of liters
s are ud for this term, multiple the results by 1000.
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Using the units specified here for the terms will result in a concentration in units of ng/mL,which is equivalent to µg/L.
8.0QUALITY CONTROL
8.1Refer to Chapter One and Method 8000 for specific quality control (QC) procedures.Quality control procedures to ensure the proper operation of the various sample preparation and/or sample introduction techniques can be found in Methods 3500 and 5000. Each laboratory should maintain a formal quality assurance program. The laboratory should also maintain records to document the quality of the data generated.
8.2Quality control procedures necessary to evaluate the GC system operation are found in Method 8000, Sec. 7.0 and includes evaluation of retention time windows, calibration verification and chromatographic analysis of samples.
8.3Initial Demonstration of Proficiency - Each laboratory must demonstrate initial proficiency with eac
h sample preparation and determinative method combination it utilizes, by generating data of acceptable accuracy and precision for target analytes in a clean matrix. The laboratory must also repeat the following operations whenever new staff are trained or significant changes in instrumentation are made. See Method 8000, Sec. 8.0 for information on how to accomplish this demonstration.
8.4Sample Quality Control for Preparation and Analysis - The laboratory must also have procedures for documenting the effect of the matrix on method performance (precision, accuracy,and detection limit). At a minimum, this includes the analysis of QC samples including a method blank, a matrix spike, a duplicate, and a laboratory control sample (LCS) in each analytical batch.
8.4.1Documenting the effect of the matrix should include the analysis of at least onesuper star是什么意思
matrix spike and one duplicate unspiked sample or one matrix spike/matrix spike duplicate pair.The decision on whether to prepare and analyze duplicate samples or a matrix spike/matrix spike duplicate must be bad on a knowledge of the samples in the sample batch. If samples are expected to contain target analytes, then laboratories may u one matrix spike and a duplicate analysis of an unspiked field sample. If samples are not expected to contain target analytes, laboratories should u a matrix spike and matrix spike duplicate pair.
8.4.2 A Laboratory Control Sample (LCS) should be included with each analytical batch.
The LCS consists of an aliquot of a clean (control) matrix similar to the sample matrix and of the same weight or volume. The LCS is spiked with the same analytes at the same concentrations as the matrix spike. When the results of the matrix spike analysis indicate a potential problem due to the sample matrix itlf, the LCS results are ud to verify that the laboratory can perform the analysis in a clean matrix.
8.4.3See Method 8000, Sec. 8.0 for the details on carrying out sample quality control
procedures for preparation and analysis.
8.5It is recommended that the laboratory adopt additional quality assurance practices for u with this method. The specific practices that are most productive depend upon the needs of the
