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Automated Gel PermeationChromatography (GPC) Clean-up of Soil

Extracts Prior to Analysis for

Semivolatile Organic Compounds byGC/MS



Agilent 6890 GC with 7683 Autosampler

and 5973 MSD



SAMPLE PREPARATION

• Standardize materials-- All reagents were pesticide grade or higher.

-- All chemicals were ACS grade quality.

-- GPC calibration standards were prepared accordingto USEPA Method 3640A and contained corn oil, bis(2-ethylhexyl) phthalate, methoxychlor, perylene andsulfur.

--Dilutions were prepared in dichloromethane ormethanol

* USEPA Method (United States Environmental Protection Agency)



-- Soil extraction was carried out utilizing pressurizedsolvent or accelerated solvent extraction (ASE) perUSEPA Method 3545.

-- Ten grams of soil was placed in a beaker and 2.5 mL ofdiatomaceous earth were added to the sample and thentransferred to an extraction cell.

-- Appropriate matrix spikes and matrix spike duplicate wasadded to each sample batch.

Soil Extraction



The samples were then extracted using a Dionex ASE 200with the

following conditions:

Oven temperature = 100 degrees C; Pressure = 1500psi Static Time = 5 minutes; Heat = 5 minutes

Flush Volume = 60%; Solvent A = 100% Nitrogen purge = 60 seconds at 150psi Extraction fluid = 1:1 dichloromethane:acetone

The sample extracts were then concentrated usingKuderna-Danish (K-D) apparatus and then reconstituted

in dichloromethane prior to GPC clean-up.



• GPC Clean-up

-- GPC clean-up was achieved using a Gilson (Middleton, WI)

Automated GX-271 GPC Clean-up System equipped with aPhenomenex (Torrance, CA) EnviroSep- ABC™GPC.

-- Sample Clean-up column with guard column. The system used a 5mL sample loop and a flow rate of 5 mL/min with dichloromethane asthe mobile phase.

-- Column calibration profiles were recorded using TRILUTION LCsoftware and a Gilson Model 112 UV Detector set at 254nm. The GPCclean-up column was calibrated using the method outlined in USEPAMethod 3640A.-- The column flow rate was verified by collected the eluate in agraduated cylinder for 10 minutes and measuring the volume. Theelution times for the corn oil, bis (2-ethylhexyl) phthalate, methoxychlor,perylene and sulfur were determined.

** (See Figure 2)



FIGURE 2



GC/MS Analysis

• Semivolatile organic compounds were analyzed byGC/MS using an Agilent 6890 GC with 7683Autosampler and 5973 MSD.

• Separation was achieved using a J&W Scientific DB5.625 , 30mm x 0.25mm x 0.25um column. The carrier

gas was Helium at a flow rate of 1.2 mL/minute. 0.5 uLof sample was injected in pulsed splitless mode withan injector temperature of 250 degrees C.

The MS conditions were as follows:

• MS Interface = 280 degrees C• MS Source = 230 degrees C• Mass Range = 35 – 500 amu• Scan Time = .317 sec/scan



Chromatogram (GC/MSD) of a soil sample that has been spiked with thesemivolatile organic compounds listed in Table 1. No GPC clean-up was

performed. Note the fronting and tailing of peaks between 8 and 12 minutes.



Chromatogram (GC/MSD) of a soil sample that has been spiked withsemivolatile organic compounds listed in Table 1.

GPC clean-up was performed. Note the improved resolution of peaks between8 to 12 minutes compared to the chromatogram in which no GPC had been

performed



CONCLUSION • The use of GPC post-extraction clean-up

improved peak resolution and reduced thepresence of fronting and tailing for the analysis ofsemivolatiles from soils.

• Recovery data was adequate for semivolatileanalysis and all compounds were withinacceptable recovery limits.

• The use of GPC clean-up also reducedmaintenance costs for the GC/MS systems sinceless contaminants were able to accumulate in theinjection port area or on the front end of thecolumn



Sample Retention Time ,(tR)(minutes)

Corn oil 10.9771

Phthalate 13.0603

Methoxychlor 14.6066Perylene 19.8885

Sulfur 23.6771

Based on the chromatography obtained, it shows thatthe soil contained 5 different samples as below :



1. Determine the Retention Factor, k for

each samples.

2.Find the Effective Plate Number, Neff



Retention factor, k = tR – tMtM

1) k corn oil = 10.9771 – 9.67919.671

= 0.134

2) k phthalate = 0.349

3) k metoxychlor = 0.509

4) k perylene = 1.055

5) k sulfur = 1.446



GRAPH ofRetention factor, k against Retention Time, T R



Given N = 7, find the value of Neff

Neff = N (k/k+1)2

1) Corn oilNeff = 7 (0.134/0.134+1)2

= 0.0977

2) PhthalateNeff = 0.469

3) MetoxychlorNeff = 0.796

4) PeryleneNeff = 1.845

5) SulfurNeff =2.446

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