STANDARD OPERATING PROCEDURE FOR THE AUTOMATED

SOXHLET EXTRACTION OF

POLYCHLORINATED BIPHENYLS (PCBs)

FROM SOILS, SEDIMENTS, WIPES AND OTHER SOLID WASTES

(SOXTEC EXTRACTION)

CRL METHOD 3541 TSCA

(TSCA PROGRAM)

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 5 CENTRAL REGIONAL LABORATORY

536 SOUTH CLARK STREET (SLO-10C)

CHICAGO, ILLINOIS 60605

DATE: April 13, 1994

CONCURRENCES:

TEAM LEADER	Erlinda Evangelista
SECTION CHIEF	Chi Tang
QC COORDINATOR	James Adams, Jr.
CRL DIRECTOR	Charles Elly

TABLE OF CONTENTS

SECTION	REV	DATE
1.0 SCOPE AND APPLICATION	0	4/94
2.0 SAFETY	0	4/94
3.0 SUMMARY OF METHOD	0	4/94
4.0 SAMPLE HANDLING AND PRESERVATION	0	4/94
5.0 INTERFERENCES	0	4/94
6.0 APPARATUS AND MATERIALS	0	4/94
7.0 REAGENTS	0	4/94
8.0 PROCEDURE	0	4/94
9.0 QUALITY CONTROL	0	4/94
10.0 REFERENCES	0	4/94

 

1.0 SCOPE AND APPLICATION

1.1 This method is a procedure for extracting polychlorinated biphenyls ( PCBs ) from soil, sediment, wipes, and other solid waste samples using an automated Soxhlet extraction unit called the Soxtec system HT2. The three-stage extraction, rinsing and concentration procedure takes about three hours to complete, about 13 hours less than what it takes the traditional Soxhlet extraction procedure. The initial extraction stage consists of immersing the thimble containing the sample in the boiling solvent under reflux for about an hour. This step facilitates a very rapid recovery of the PCBs due to the close contact of the sample with the solvent. The second stage rinses the thimble which has now been elevated above the solvent. In the final stage, concentration is brought about by closing the condenser valve, and allowing the solvent to evaporate until the volume of the extract is about 2-5 ml. Meanwhile, the evaporated solvent is being recovered in the condenser.

1.2 This method is applicable to the extraction and concentration of PCBs prior to gas chromatographic analysis. The following compounds can be extracted using this method: Aroclor 1016, Aroclor 1221, Aroclor 1232, Aroclor 1242, Aroclor 1248, Aroclor 1254, and Aroclor 1260. The detection limit is determined according to the action level. In general. The detection limit is 20% of the action level.

1.3 The extracts from this procedure should be subjected to Florisil column and acid clean-up procedures in order to eliminate interferences. If sulfur is present, as evidenced by a huge peak early in the chromatogram, then the extract will have to be treated with mercury to eliminate the sulfur. Sulfur will mask the early eluting peaks of the Aroclor.

Refer to CRL Methods 3660-SULFUR and 3600-ACID for the Clean-up procedures.

2.0 SAFETY

2.1 The toxicity or carcinogenicity of each reagent used in this procedure has not been precisely defined; however, each chemical compound should be treated as a potential health hazard. Exposure to any of these chemicals should be reduced to the lowest possible level by whatever means available. extreme caution. Preparation of stock, intermediate, and working standards should be carried out in a hood.

3.0 SUMMARY OF METHOD

3.1 The soil/sediment sample is mixed with anhydrous sodium sulfate, placed in the extraction thimble and topped with clean glass wool, and extracted with 50 ml of 1:1 (v:v) acetone/hexane in a Soxtec System HT2. At the end of one hour, the thimble is elevated above the solvent and rinsed for an hour. In the third and final stage, the sample extract is concentrated by closing the condenser valve thus preventing the solvent from circulating back into the extraction cup. The solvent is recovered in the condenser.

The entire wipe sample is extracted in the same manner as above, except for the addition of sodium sulfate. Dry, solid wastes ( such as wood chips, paper, steel cuttings, and other unusual, non-routine matrices ) should be either ground, cut, pulverized, and reduced in size through appropriate means prior to extraction.

4.0 SAMPLE HANDLING AND PRESERVATION

4.1 The samples for this procedure are collected in clear glass bottles, approximately 8 oz. capacity, with Teflon-lined screw caps, and properly identified with sample tags.

4.2 The samples must be refrigerated at 4 deg C from the time of collection until extraction.

4.3 The samples must be extracted within 14 days of collection and analyzed within 40 days of extraction.

5.0 INTERFERENCES

5.1 Method interferences may be caused by contaminants in solvents, reagents, glassware and other sample processing hardware that lead to discrete artifacts or elevated baselines in gas chromatograms. All of these materials must be routinely demonstrated to be free from interferences under the conditions of the analysis by running laboratory reagent blanks.

5.1.1 Glassware must be scrupulously cleaned. Clean all glassware as soon as possible after use by rinsing with the last solvent used in it, followed by detergent washing with hot water and rinses with tap water and distilled water. Heat the dry glassware in a drying oven at 400 deg C for about 30 minutes or at 130 deg C for 12 hours or more.

Note:See the SOP for washing of glassware at the  CRL.

5.1.2 The use of high purity reagents and solvents will greatly minimize interference problems.

5.2 Interferences by phthalate esters can pose a major problem when using an electron capture detector. These compounds generally appear in the chromatogram as large late eluting peaks. Avoiding the use of common flexible plastics that contain varying amounts of phthalates will minimize this type of interference problems.

5.3 Matrix interferences may be caused by contaminants that are coextracted from the sample. The extent of interferences will vary. Clean up procedures will eliminate certain types of interferences.

6.0 APPARATUS AND MATERIALS

6.1 Automated Soxhlet Extraction System - Soxtec System HT2, or equivalent consists of the following:

6.1.1 Extraction unit - has a dual-sample extraction capability; heating is brought about by circulating hot silicone oil through the heating plates from a service unit.

6.1.2 Service Unit ( 1046 Soxtec service Unit ) - equipped with a pump that circulates the hot oil through the heat transfer tubings to the heating plate in the extraction unit. The temperature control is a completely electronic system with digital display for actual temperature and set point. The unit is settable from ambient to 200 deg C.

NOTE: For details on the operation, safety features and maintenance of the service unit, see the 1046 Service Unit Instruction Manual.

6.1.3 Extraction cups - preferably glass

6.1.4 Extraction Tongs

6.1.5 Thimbles - 33 mm ID x 80 mm

6.1.6 Thimble Adapter - 33 mm ID

6.2 Analytical Balance - capable of weighing to the nearest 0.0001 g

6.3 Drying oven

6.4 Desiccator

6.5 Glass wool

6.6 Volumetric flasks - 10 ml

7.0 REAGENTS

7.1 Solvents

7.1.1 Acetone - pesticide quality

7.1.2 Hexane - pesticide quality

7.2 Spiking solutions

7.2.1 PCB spiking solution - See Section 8.3.2 and 9.1.1 for details on the level and spiking compound to be used

7.3 Sodium sulfate - ACS, granular, anhydrous. Purify by heating at 400 deg C for at least 4 hours.

8.0 PROCEDURE

8.1 Sample Handling

8.1.1 Soil/sediment samples - Mix the sample thoroughly, especially composited samples. Decant and discard any water layer. Discard any foreign objects such as sticks, leaves and rocks.

8.1.2 Wipes - the entire wipe is extracted.

8.1.3 Solid wastes - Dry, solid wastes (such as wood chips, paper, steel cuttings, and other unusual matrices) should be either ground, cut, pulverized and reduced in size through appropriate means prior to extraction.

8.1.4 Information about the action level should be obtained from the requestor, if not already specified in the request form.

8.2 Dry weight determination (% Total Solids)

Results should be reported on a dry weight basis, unless otherwise instructed by the requestor. To proceed with this determination, a portion of sample should be weighed out at the same time as the portion used for extraction, as follows:

8.2.1 Immediately after weighing the sample for extraction, weigh 5-10 g of the sample into a tared crucible. Let stand to air-dry in a well-ventilated hood for 12 hours or more. Weigh the dried sample. Repeat the drying process until weight is constant.

8.2.2 Calculate the dry weight as follows:

% Total solids = Weight of dry sample (g) x 100

                             Weight of sample (g)

8.3 Automated Soxhlet Extraction

8.3.1 Weigh out 10 g of samples. Weigh duplicate portions of the sample selected for spiking and add the spiking solution before proceeding to the next step. The level of spiking should be consistent with the action level for the particular site or study. For example, if the action level is 50 ppm, then spike at 50 ppm. If at all possible, pre-screen the samples and use the least contaminated sample for spiking. If PCB is present, then spike with the same type of PCB. In the case of wipe samples, proceed with step 8.3.3.

8.3.2 If the sample looks too watery, air-dry for a few hours before adding sodium sulfate. Otherwise, if too much sodium sulfate is added, the mixture may not fit in the thimble. Mix until the sample looks dry and powdery.

8.3.3 Place the sample in the extraction thimble. Place a plug of glass wool on top of the sample.

8.3.4 Before proceeding with the extraction, perform the following steps:

8.3.4.1 Check the oil level in the service unit. Add oil if necessary.

8.3.4.2 Press the POWER button, observe that the switch lamp is on.

8.3.4.3 The overheat temperature should have been previously preset, if not, set according to temperature scale, using a screwdriver. The overheat temperature should be set about 5 degrees higher than the operating temperature.

8.3.4.4 Press READ/SET switch so the SET lamp lights up. The display now gives set point. Adjust to the desired operating temperature by turning the SET know. The operating temperature for this SOP is 120 deg C.

8.3.4.5 Press READ/SET switch again so that the SET lamp goes of and the display shows actual temperature. During the heating up period the HEAT lamp lights up. Once the temperature has reached the set point, the READY lamp lights up. The unit is now ready for operation.

8.3.4.6 Open the cold water tap for the reflux condensers. Adjust the flow to 2 L/min to prevent solvent evaporation from the condensers. This flow was based arbitrarily on an assumed cooling water temperature of about 15 deg C.

8.3.5  Attach the thimble containing the sample to the adapter. Move the extraction mode knob to the BOILING position. Insert the thimble into the condenser. The magnet at the bottom of the condenser will now fasten to the thimble adapter. Each extraction place in the unit has its own controls for independent operation.

8.3.6  Lower the knob to the RINSING position so that the thimble will now hang just below the condenser valve.

8.3.7  Press down the heating plate handle and insert the extraction cup containing one or two boiling chips and 50 ml of 1:1 ( v:v ) acetone/hexane. Ensure that the cup is positioned on the heating plate in such a way that the condenser rim is flushed with the rim of the extraction sup when the heating plate handle is released.

8.3.8  Release the heating plate handle. The cup is now clamped into the condenser.

8.3.9 Move the extraction mode know to the BOILING position. This will immerse the thimble in the solvent. Set the timer for 60 minutes. Ensure that the condenser valve is open (vertical position).

8.3.10 At the end of one hour, move the knob to the RINSING position, this allowing the thimble to hang just above the surface of the solvent. Set timer for another 60 minutes and, with the condenser valve still in the open position, continue heating for the preset time.

8.3.11 When the rinse time has elapsed, close the condenser valve by turning about a quarter turn (horizontal position).

8.3.12 Continue heating in order to concentrate the extract to about 2-5 ml. The solvent will be recovered in the condenser. Ensure that the condenser valve can be tightened properly.

8.3.13 Remove the cup and quantitatively transfer the contents to a 10 ml volumetric flask. Make up the volume to 10 ml with hexane.

8.3.14 Proceed with the clean-up procedure.

8.4 Clean the extraction unit between samples by rinsing with 50 ml of solvent for 15 minutes. If the site is known to be highly contaminated with PCBs, then a second rinse may have to be performed.

8.5 Turn off the service unit after use.

8.6 Turn off the cold water tap.

9.0 QUALITY CONTROL

9.1 The laboratory is required to operate a formal quality control program. The minimum requirements of this program consist of an initial demonstration of laboratory capability and an ongoing analysis of method blanks, spiked samples and laboratory control standards to evaluate and document data quality. Ongoing data quality checks are compared with established performance criteria to determine if the results of the analysis meet the criteria.

9.1.1 Method blank: The method blank is carried through the entire procedure. It should be free of contamination by the parameters of interest. A method blank is run with every set of 10 samples or each day of extraction.

9.1.2 Matrix spike/matrix spike duplicate: The matrix spike and matrix spike duplicate are carried through the entire procedure and the recovery results are compared with established limits. The relative results are compared with established limits. The relative percent difference ( RPD ) between duplicate spikes is calculated and is a measure of method precision. MS/MSD samples are run for every data set and matrix type in the data set. For a large study ( same site ) consisting of several data sets, MS/MSD are run for every 20 samples.

9.1.3 Spike the soil/sediment sample selected as MS/MSD at a level consistent with the action level for the particular site or study. If the solid waste is amenable to spiking, spike duplicate portions of the sample in the same manner as the soil.

Wipe samples are not spiked. If wipe samples are extracted along with soil samples, then the QC associated with the extraction batch will apply only to the wipes. If wipes alone are extracted, then a laboratory control standard should be subjected to the same clean-up procedures as the wipe extract.

9.1.4 For each clean-up procedure that the extracts are subjected to, run a solvent blank and a laboratory control standard.

10.0 REFERENCES

1. SW-846 Revision 0 November 1990 Method 3541, AAUTOMATED SOXHLET EXTRACTION@

2. Soxtec System HT2 Operating Manual, Tecator, Part NO. 1000 2296

3. Soxtec Service Unit Operating Manual, Tecator, Part No. 1000 3817