STANDARD OPERATING PROCEDURE
ANALYSIS OF METHYL PARATHION IN WIPE SAMPLES
BY GAS CHROMATOGRAPHY
US EPA REGION 5
CENTRAL REGIONAL LABORATORY,
1 Scope and Application:
1.1 This procedure is for extracting methyl parathion from solids such as cotton balls and gauze used in wipe sampling. The wipe samples are extracted using the Accelerated Solvent Extraction (ASE) technique. For liquid samples containing high levels of methyl parathion, no extraction would be performed. Instead the liquid sample is first diluted then identified and quantified by gas chromatography/mass spectrometry using the selected ion monitor (SIM) technique.
1.2 This method is restricted to use by or under the supervision of analysts experienced in extraction techniques and in the use of a gas chromatograph (GC). The entire method should be read before beginning the extraction.
1.3 It is recommended that samples with expected high concentrations of methyl parathion should be first screened with the gas chromatography/mass spectrometry (GC/MS) selective ion monitor (SIM) method. The GC/MS SIM screening will help the GC analyst prepare appropriate dilutions prior to GC injection to protect the GC detector.
2.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely defined; however, each chemical compound should be treated as a potential health hazard and exposure to these chemicals should be reduced to the lowest possible level by whatever means available.
2.2 Methyl parathion is very light sensitive and extreme caution should be taken to protect from any sources of UV light. MSDS sheets concerning the use of methyl parathion and ethyl acetate should be read before performing any extractions.
3.0 Summary of Method
3.1 Wipe samples are collected over a fixed areas of surface (usually 100 cm2). The wipe material contains isopropyl alcohol solvent to dissolve the desired analyte. Upon receipt, the entire wipe sample is quantitatively transferred to the extraction vessel. It is then extracted using the ASE extraction apparatus with ethyl acetate. The final volume of the extract is adjusted to the final volume of 50 ml with ethyl acetate. The extract is then injected into a GC equipped with an electron capture detector (ECD) or a nitrogen/phosphoric detector (NPD) and a primary column for quantitation. Confirmation of methyl parathion is done with a secondary GC column or GC/MS SIM technique if the concentration of methyl parathion is high enough for GC/MS SIM detection.
3.2 All information should be carefully noted on log sheets, especially the type and number of wipes on each sample. Be sure to indicate if cotton balls or gauze wipe material are used for this method.
4 Sample Handling and Preservation
All samples should be stored around 4 deg C before extraction. All samples should be extracted within seven days of sample collection. Sample extracts should be stored in amber vials and analyzed within 40 days of extraction. The analyst should write down in the sample preparation sheet the number of wipes contained in each sample container and condition of wipes such as relative amount of dirt/dust, color, and presence of Isopropanol.
5.1 Method interferences may be caused by contaminants in solvents, reagents, glassware, and other sample processing hardware that lead to discrete artifacts and elevated baselines in gas chromatograms. The use of high purity reagents and scrupulously clean glassware helps to minimize interference problems.
5.2 Matrix Interferences may be caused by contaminants that are co-extracted from the sample. The extent of interferences may vary considerably from source to source depending upon the nature and diversity of the place sampled.
6 Apparatus, Instruments, and Materials
6.1 Accelerated Solvent Extraction (ASE): A Dionex ASE 200 system is used for extraction of all wipes samples for the analysis of methyl parathion. The system includes the operation control panel, extraction cells, and collection vials.
6.1.1 Extraction cells: Three different sizes, 11-ml, 22-ml and 33-ml extraction cells are used for extraction of wipes.
6.1.2 Collection vials: 60 ml size amber vials are used for collection of extracts.
6.1.3 Filter: Grade D28, 1.91 cm circle filter paper is used to filter extracts from extraction cells to collection vials.
6.2 Gas Chromatograph (GC): An analytical system complete with GC suitable for on-column injections and all required accessories including electron capture detector (ECD) and/or nitrogen/phosphorus detector (NPD), column supplies, gases and an autosampler. A data system should be used for data acquisition and processing.
6.2.1 Gas Chromatographic Column
184.108.40.206 Primary column: DB-5, 30 m x 0.53 mm ID x 1.5 uM film thickness
220.127.116.11 Secondary column: DB-608, 30m x 0.53 mm ID x 0.83 uM film thickness
6.4.1 Ethyl Acetate - Reagent Grade
6.4.2 Methyl Parathion Standard - 1000 ug/ml stock solutions, reagent grade, purchased from two supplies, one for calibration of the instruments, the other for verification of the calibration.
6.4.3 Vials- 2 ml autosampler amber vials with teflon-lined crimp tops and 60 ml collection amber vials.
6.4.4 Syringes - 0.2 ml, 0.5 ml, and 5.0 ml sizes.
6.4.5 Micro Syringes - 10 uL and larger.
6.4.6 Sand - Ottawa Sand
7 Equipment and Instrument Conditions
7.1 ASE 200 Operating Conditions
100 deg C
Oven Heat-up Time:
60 % of extraction cell volume
100 % ethyl acetate
7.2 Gas Chromatograph Operating Conditions
250 deg C
350 deg C
Carrier & Make-up Gas
50 ml/min total flow rate &(ultra high purity nitrogen) 6 ml/min column flow rateOven Temperature Program
200 deg C
10 deg C/min
250 deg C
20 deg C/min
Final Temperature A
280 deg C
Final Time A
8 Extraction Procedures
8.1 Three sizes of cells, 11-ml, 22-ml, or 33-ml cell, can be used for extraction. Take a clean and dried cell, first put a 1.91 cm circle filter on the bottom of the cell, then add a layer of sand, finally transfer the wipes form the sample container to the cell. Make sure to separate and count the number of wipes in each sample container and write down on the bench sheet or the log book.
8.2 Add indicated amount of surrogate to all samples including the blank, and LCS/LCS duplicate samples. The surrogate compound currently used is Tetrachloro-m-xylene (TC MX).
8.3 Add indicated amount of methyl parathion spike solution to the LCS and LCS duplicate samples. The amount of methyl parathion spiked to LCS and LCS duplicate samples should be about the middle level of the calibration range.
8.4 Add sand to cover samples up to the top of the extraction cell, then cap and place the extraction cells into the autosampler tray.
8.5 Load the collection tray with the appropriate number (one per sample) of 60-ml, cleaned, capped amber vials with septa.
8.6 Start ASE extraction following the extraction conditions specified in Section 7.1.
8.7 After the extraction is done. The extract is ready for injecting into the GC and/or GC/MS instruments. Cleanup should not be required, but methods are available if needed. If sample is cloudy, the analyst may need to filter it with the same type of filter used for GPC cleanup.
9 Quality Control and Corrective Action
9.1 The method detection limit (MDL) is defined as the minimum concentration of substance that can be measured and reported with 99 % confidence that the value is greater than zero and is determined from analysis of a sample in a given matrix containing the analyte. The MDL determination on the proper matrix should be run before use and after any significant modifications.
9.2 Initial Demonstration of Precision and Accuracy - A initial precision and accuracy study must be performed by analyzing four replicate blank wipes spiked with methyl parathion in the mid range of the calibration.
9.3 Instrument Calibration - The GC must be calibrated initially and on an ongoing basis according to the procedures in Section 10.
9.4.1 Sand Blank- Laboratory blanks consisting of the sand should be processed as a sample at least once with each batch/bottle of sand opened. The sand is baked overnight at 100 deg C then cooled to room temperature before use. The sand blank is spiked with surrogate standard and extracted with samples.
9.4.2 Method Blank - One or two blank gauzes (depending on project needs) are saturated with isopropanol, spiked with surrogate and extracted as a sample for every 10 samples or at a frequency specified by the project.
9.4.3 Field Blank- One field blank soaked with isopropanol is collected for each residence or at a frequency specified by the project .
9.5 Laboratory Control Spikes (LCS) - One or two blank gauzes (depending on project needs) are saturated with isopropanol, spiked with surrogate and methyl parathion, and then extracted and analyzed with every 20 samples.
9.6 LCS Duplicate - A second LCS samples is prepared as in Section 9.5 to determine method precision. One LCS-Duplicate for each LCS.
9.7 Surrogate Spike - Each QC, Blank, and sample is spiked with surrogate compound prior to extraction. However, due to high concentrations of methyl parathion in the samples, the surrogate spike is routinely diluted out on many samples.
9.8 Qualitative Confirmation- The relative retention time of methyl parathion in samples is tracked by comparing the relative retention time (rrt) of sample to standard within "3 standard deviation. In addition, a second, dissimilar GC column is used to determine if methyl parathion and surrogate were positively identified by both rrts.
10.1 Initial Calibration - After the MDL study is completed, the lowest point on the calibration curve should be established near but above the MDL. The linear range should be established by running at a minimum of five level standards at increasing concentration. The upper calibration range should be established at the highest linear concentration without saturating the detector. The % RSD of the relative response factors should be calculated and be less than or equal to 30 %. The external calibration curve should have a corr coefficient of no less than 0.995.
10.2 Calibration Verification Standard (CVS) - Prepare a calibration verification standard for assessing the accuracy of the working calibration standards. Verification of the working standards should be done periodically or whenever quantitation problems arise. Purchase the calibration verification standard from a different supplier.
10.3 Continuing Calibration - A calibration standard in the midpoint of the curve should be analyzed after each 10 samples and its % D from the average R.F. of the initial calibration should be less than or equal to 25 %.
11 Pollution Prevention
The ASE uses 50 ml extraction solvent for each sample as opposed to Soxtec (100 ml) and soxhlet (350 ml). Ethyl acetate is not concentrated, removing the possibility of solvent vapor escaping the lab. Ethyl acetate is also less hazardous than traditional solvents (e.g., methylene chloride, acetone and hexane) used for extraction.
1 AMethod 3545: Accelerated Solvent Extraction@, Test Methods for Evaluating Solid Waste, SW-846, Revision 0, January 1995.
2 AMethod 8081: Organochlorine Pesticides by GC, capillary column technique@, Test Methods for Evaluating Solid Waste, SW-846, 3rd edition.
3 AMethod 8141A: Organophosphorus Compounds by GC, capillary column technique@, Test Methods for Evaluating Solid Waste, SW-846, 3rd edition.