Analysis of semi-volatile organic compounds (SVOCs) in soil and sediment requires extensive sample cleanup to remove interfering matrix components such as lipids, sulfur, and humic substances. Gel permeation chromatography (GPC) separates compounds by molecular size and is widely used for this purpose. Chinese standard HJ 834-2017 specifies GPC as a cleanup technique for SVOC determination. This solution describes a GPC method for purifying soil and sediment extracts prior to GC-MS or HPLC analysis. The performance is validated using a calibration mixture containing corn oil, di(2-ethylhexyl) phthalate (DEHP), methoxychlor, perylene, and sulfur.
GPC calibration solution
Contains corn oil (25 mg/mL), DEHP (1 mg/mL), methoxychlor (200 mg/L), perylene (20 mg/L), and sulfur (80 mg/L) in dichloromethane/acetone (1:1).
SVOC standards
Individual or mixed standards for target analytes (e.g., PAHs, pesticides) as needed.
Internal standards
1,4-Dichlorobenzene-d4, naphthalene-d8, acenaphthene-d10, phenanthrene-d10, perylene-d12, pyrene-d12 (optional).
Surrogate standards
Phenol-d6, 2-fluorophenol, 2,4,6-tribromophenol, nitrobenzene-d5, 2-fluorobiphenyl, 4,4'-terphenyl-d14 (optional).
Solvents
Acetone, dichloromethane, cyclohexane (all pesticide residue grade or HPLC grade).
Other materials
Anhydrous sodium sulfate, diatomaceous earth, glass wool, etc.
Standard Solution Preparation
GPC calibration solution: Prepare as described above or obtain commercially.
SVOC stock solutions: Prepare individual or mixed standards at concentrations of 1000–5000 mg/L in dichloromethane/acetone (1:1).
Internal standard solution: Dilute to 200–500 μg/mL in dichloromethane/acetone (1:1).
Surrogate standard solution: Dilute to appropriate concentration.
Sample preparation
Air-dry or freeze-dry soil/sediment samples, grind, and remove debris. Weigh 20 g (to 0.01 g) of fresh sample, mix with drying agent (anhydrous Na₂SO₄ or diatomaceous earth) until free-flowing.
Extraction
Perform Soxhlet extraction for 16–18 h with 100 mL dichloromethane/acetone (1:1), or use pressurized fluid extraction (according to HJ 783).
Concentration
Concentrate the extract to about 2 mL under nitrogen or rotary evaporator. Exchange solvent to GPC mobile phase (dichloromethane/acetone 1:1) and concentrate to 1 mL.
GPC cleanup: Inject the concentrated extract into the GPC system. Collect the fraction containing target SVOCs (typically after corn oil elutes and before sulfur elutes). Concentrate the collected fraction to 1 mL and add internal standard.
GPC System
Typically part of an HPLC system with Isocratic pump, UV or RI detector (optional, for calibration), Fraction collector, GPC column (e.g., based on styrene-divinylbenzene, 300–600 mm length).
Pretreatment equipment
Soxhlet extractor, nitrogen evaporator, rotary evaporator, analytical balance, etc.
GPC Calibration
The GPC calibration solution was injected to determine the elution profile and collection window. The chromatogram (Figure 1) shows the following peaks: corn oil, DEHP, methoxychlor, perylene, and sulfur. Resolution between critical pairs meets the requirements of HJ 834-2017. The GPC calibration parameters were shown in Table 1.
Figure1. GPC chromatogram of calibration mixture (corn oil, DEHP, methoxychlor, perylene, sulfur)
Table 1. GPC calibration parameters
| Peak | Compound | Retention Time (min) | Resolution | HJ 834-2017 Requirement |
|---|---|---|---|---|
| 1 | Corn oil | 7.27 | – | – |
| 2 | Di(2-ethylhexyl) phthalate | 9.91 | 1.14 | ≥ 0.85 |
| 3 | Methoxychlor | 11.76 | 0.87 | ≥ 0.85 |
| 4 | Perylene | 16.00 | 1.92 | ≥ 0.85 |
| 5 | Sulfur | 18.24 | 0.97 | ≥ 0.90 |
All resolution values meet or exceed the standard requirements, confirming proper column performance.
Collection Window Determination
Based on the calibration, the collection window for SVOCs is set from after the corn oil peak (ca. 8 min) to before the sulfur peak (ca. 18 min). This ensures that high-molecular-weight interferences are excluded while target analytes are recovered.
Application to Samples
The GPC method is suitable for cleaning up soil and sediment extracts prior to GC-MS or HPLC analysis of SVOCs. The purified extract is free of major interferences, allowing accurate quantification.
The described GPC method provides effective cleanup for soil and sediment extracts, achieving the resolution required by HJ 834-2017. It is a reliable tool for preparing samples for SVOC analysis by chromatographic techniques.
