EPA Method 525.2: Extract SVOCs from Drinking Water Using the Empore™ C18 SPE Disk
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Authors: Xiaohui Zhang, Guotao Lu
Study summary: A validated EPA Method 525.2 workflow using the Empore™ 47 mm C18 SPE Disk extracts 102 semi-volatile organic compounds from 1 L drinking water samples spiked at 2 µg/L. 89 compounds achieved recovery above 85% with average RSD 4.7%, and 98 of 102 compounds fell within the 70%–130% range required by EPA Method 525.2 — making the Empore C18 disk a qualified solution for drinking water monitoring of pesticides, PCBs, phthalates, and PAHs.
TL;DR: EPA Method 525.2 demands processing 1 L of drinking water at pH 2 — conditions that strip C18 phase from many SPE disks and ruin GC/MS chromatograms. The Empore™ C18 SPE Disk holds up to these conditions and validates 98 of 102 compounds within the EPA-required 70%–130% recovery window. The 4 low-recovery exceptions (Atraton, Simetryn, 2,4-DNT, 2,6-DNT) are scientifically explained — and addressable with the Empore SDB-RPS disk for polar compounds.
Study at a Glance
Introduction: Why EPA Method 525.2 Is the Drinking Water SVOC Standard
The target analyte list for EPA Method 525.2 covers 110 organic compounds across four classes:
Pesticides
Polynuclear aromatic hydrocarbons (PAHs)
PCBs (polychlorinated biphenyls)
Phthalates and adipates
Method detection limits (MDLs) published in EPA 525.2 range from 0.03 to 2.4 µg/L, and individual recovery rates vary from 20% to 180% across the analyte list. Averaged by compound class, the EPA-published recovery rates are:
Pesticides: 108%
PCBs: 108%
Phthalates & Adipates: 116%
PAHs: 112%
EPA Method 525.2 specifically specifies SPE disks as the sample preparation tool for cleanup and concentration of organic contaminants from drinking water samples. There are two well-known challenges in this method's sample preparation:
Large sample volume — 1 liter per extraction
Low pH — around pH 2
Why disk integrity matters: EPA Method 525.2 specifically warns that stripping C18 phase from the extraction disk packing will complicate chromatographic analysis with high background, which can obscure testing results on compounds of interest. Empore™ C18 disks consistently handle 1 L volumes at pH 2 without loss of C18 phase from the silica support.
In this application note, a 1 L drinking water sample was passed through a 47 mm C18 Empore™ disk and eluted with ethyl acetate and methylene chloride under negative pressure. The extract was then dried, reduced in volume to 1.0 mL, and analyzed by GC/MS. Validation data was determined from three repeats (n=3) using the same lot of C18 disks.
Headline result:
89 of 102 compounds achieved recovery > 85% with average RSD 4.7%
An additional 9 compounds achieved recovery 70%–84% with average RSD 7.8%
98 of 102 compounds fell within the 70%–130% range required by EPA Method 525.2
Only 4 compounds showed recovery below 70% — each with a documented scientific cause
Why the Empore™ C18 Disk for EPA Method 525.2
EPA Method 525.2 places two demanding requirements on the SPE format: 1 L sample volume and pH 2 acidic conditions. The Empore™ C18 47 mm disk delivers on both:
Resistant to C18 phase loss — the particle-loaded PTFE membrane keeps C18-bonded silica securely in place even at low pH, preventing high chromatographic background
High flow rate for 1 L samples — disk format processes large volumes faster than cartridge SPE
Clean chromatograms — minimal interference from disk components, critical for EPA 525.2 GC/MS analysis
Validated across 4 compound classes — pesticides, PAHs, PCBs, phthalates & adipates all covered in a single workflow
Materials
Chemicals
525.2 analytes — AccuStandard (New Haven, CT)
Sodium sulfite — Sigma-Aldrich (St. Louis, MO)
Methylene chloride, Ethyl Acetate, Methanol — high purity pesticide quality, Burdick & Jackson (Muskegon, MI)
SPE Media
Empore™ C18-bonded silica disk, 47 mm — CDS Analytical Part #2215 (also available as Fisher Scientific 13-110-018 / VWR 76333-132)
GC/MS Configuration
Instruments: Shimadzu GC-2010 Gas Chromatograph with split/splitless injection portal, interfaced to Shimadzu GC-MS QP2010 (Kyoto, Japan)
GC Parameters
Oven Temperature Program
Mass Spectrometer Parameters
Validated EPA Method 525.2 SPE Procedure
1. Sample Pre-treatment
Add 40 mg sodium sulfite to 1 L of tap water to reduce free chlorine. Adjust the water sample to pH = 2 using 6 M HCl. Add 5 mL of methanol as a wetting agent.
Each sample is fortified with 2 µg of each internal standard and surrogate. For recovery measurements, each sample is also fortified with 2 µg of each method analyte (resulting in a 2 µg/L (2 ppb) spike level).
2. SPE Procedure (12-Step Protocol)
Assemble an all-glass filtration apparatus using a 47 mm C18 Empore™ disk. (A manifold for multiple extractions is acceptable.)
Wash the apparatus and disk by adding 5 mL of 1:1 ethyl acetate/methylene chloride (EtAc/MeCl₂) to the reservoir. Pull a small amount through the disk under vacuum, then turn off vacuum and let the disk soak for ~1 minute. Pull remaining solvent through and let the disk dry.
Condition the disk: add ~5 mL methanol. Pull a small amount through, soak ~1 minute, then pull most through, leaving 3–5 mm of methanol on the disk surface.
Equilibrate: add 5 mL reagent water and pull most through, again leaving 3–5 mm of water on the disk surface.
Add wetting agent to sample: add 5 mL methanol to the water sample and mix well.
Sample loading: add the water sample to the reservoir and filter under vacuum as quickly as it will allow. Drain as much water as possible from the sample bottle.
Remove the filter assembly and insert a suitable sample tube for eluate collection.
Elution Step 1 (EtAc): add 5 mL EtAc to the original sample bottle, rinse thoroughly, and transfer the solvent to the disk with a dispo-pipet, rinsing the sides of the filtration reservoir.
Pull half of the solvent through the disk, then release the vacuum. Let the disk soak ~1 minute, then draw remainder under vacuum.
Elution Step 2 (MeCl₂): repeat the solvent rinse of the bottle and apparatus using 5 mL methylene chloride.
Final rinses: using a disposable pipette, rinse down the sides of the filtration glassware with two 3 mL aliquots of 1:1 EtAc/MeCl₂.
Drying: dry the combined eluate with 5–7 g of granular anhydrous sodium sulfate. Rinse the collection tube and sodium sulfate with two 3 mL portions of 1:1 EtAc/MeCl₂ and combine into a concentrator tube.
3. Concentration
Concentrate the extract to 1 mL under a gentle stream of nitrogen (may be warmed gently).
Critical concentration note: Do not concentrate to less than 0.5 mL — analyte loss may occur.
Results and Discussion
Figure 1 shows the GC chromatogram of 102 semi-volatile compounds from EPA Method 525.2. Under these conditions, all 102 compounds are well separated. Table 1 (below) lists the recovery and RSD data for each compound across n=3 replicates.
Overall Recovery Performance
Performance summary across 102 compounds:
89 compounds (87.3%) — recovery > 85%, average RSD 4.7%
9 compounds (8.8%) — recovery 70%–84%, average RSD 7.8%
98 of 102 compounds (96.1%) within the EPA-required 70%–130% range
4 compounds (3.9%) below 70% recovery — each with documented scientific cause (see below)
Why Four Compounds Show Low Recovery — and How to Fix It
Four of the 102 tested compounds showed recovery below 70% in this study. Each has a documented mechanistic explanation, and for two of them, the Empore™ SDB-RPS disk offers a validated alternative.
Practical recommendation: If your target analyte list includes dinitrotoluenes, triazine herbicides, or other highly polar compounds, the Empore™ SDB-RPS disk — which combines reversed-phase and strong cation exchange (SCX) chemistry — provides better retention through ionic interactions and significantly improves recovery for these polar analytes.
Table 1 — Average Recovery and RSD for 102 EPA 525.2 Compounds
Conclusion
A simple and effective method for extracting organic compounds from 1 L drinking water samples using Empore™ C18 47 mm SPE disks has been validated per EPA Method 525.2. Of the 102 organic compounds tested at 2.0 µg/L:
89 compounds exceeded 85% recovery with average RSD 4.7%
9 compounds recovered between 70% and 84% with average RSD 7.8%
98 of 102 compounds fell within the 70%–130% range required by EPA 525.2
The 4 low-recovery exceptions all have documented mechanistic causes
The data supports that CDS Empore™ C18 disks are qualified for screening drinking water samples per EPA Method 525.2, as well as for monitoring phthalates, organochlorine pesticides, triazine herbicides, and PAHs in drinking water more broadly. For polar compounds where C18 retention is limited, the Empore SDB-RPS disk offers a complementary mixed-phase solution.
Frequently Asked Questions
What is EPA Method 525.2 used for?
EPA Method 525.2 is the U.S. EPA's standard method for determining organic compounds in drinking water by liquid-solid extraction (SPE) and capillary column gas chromatography/mass spectrometry. The target analyte list contains 110 compounds across four classes: pesticides, polynuclear aromatic hydrocarbons (PAHs), PCBs, and phthalates and adipates.
What recovery rates does the Empore C18 Disk achieve for EPA 525.2?
In a validated 1 L drinking water workflow at a 2 µg/L spike level (n=3), 89 of 102 tested compounds achieved recovery above 85% with average RSD 4.7%. An additional 9 compounds showed recovery between 70% and 84% with average RSD 7.8%. Overall, 98 of 102 compounds fell within the 70%–130% range required by EPA Method 525.2.
Why does EPA Method 525.2 require SPE disks instead of cartridges?
EPA Method 525.2 specifies SPE disks because the method requires processing 1 liter of drinking water at low pH (around pH 2). The Empore C18 disk handles these challenging conditions consistently without loss of C18 phase from the silica support. EPA Method 525.2 specifically warns that stripping of C18 phase complicates chromatographic analysis with high background that can obscure target compound results.
Why is sodium sulfite added to the water sample in EPA 525.2?
Sodium sulfite (40 mg per 1 L water sample) is added to reduce free chlorine in tap water before extraction. Chlorine in drinking water can interfere with the SPE process and degrade target analytes. Sample pH is then adjusted to 2 using 6 M HCl, and 5 mL of methanol is added as a wetting agent.
Which Empore C18 disk SKU is used for EPA 525.2?
The Empore™ C18-bonded silica disk, 47 mm, is used for EPA 525.2. CDS Analytical Part #2215 (also available as Fisher Scientific 13-110-018 and VWR 76333-132). The procedure uses one disk per extraction with elution by ethyl acetate and methylene chloride under negative pressure.
Why do some compounds show low recovery in EPA 525.2?
Four compounds in this study showed recovery below 70%: Atraton (58%), 2,4-Dinitrotoluene (42%), 2,6-Dinitrotoluene (45%), and Simetryn (65%). For Atraton and Simetryn, the low recovery is caused by polar groups in diamino-1,3,5-triazine type compounds that interact poorly with reversed C18 phase at pH 2. For the dinitrotoluenes, the polarity causes poor retention on reversed C18 and breakthrough during sample loading. The Empore SDB-RPS disk (a mixed reversed-phase/strong-cation-exchange phase) recovers both dinitrotoluenes at >80% and is recommended when these compounds are critical.
Can the Empore C18 Disk be used for compounds other than the EPA 525.2 list?
Yes. Beyond the EPA 525.2 analyte list, the Empore C18 Disk is qualified for screening drinking water samples per EPA Method 525, and for monitoring phthalates, organochlorine pesticides, triazine herbicides, and PAHs in drinking water more broadly. For polar compounds that show poor recovery on C18, the Empore SDB-RPS disk is a recommended alternative.
What sample volume is required for EPA 525.2?
EPA Method 525.2 requires processing 1 liter (1 L) of drinking water sample. This large sample volume — combined with the low pH (~2) requirement — is one of the two main extraction challenges of the method. The Empore C18 disk format is designed to handle 1 L volumes consistently at controlled flow rates under vacuum.
References
U.S. Environmental Protection Agency. Method 525.2: Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and Capillary Column Gas Chromatography/Mass Spectrometry, Revision 2.1. Environmental Monitoring Systems Laboratory, Office of Research and Development, U.S. EPA, Cincinnati, OH 45268.
National Primary Drinking Water Regulations; Analytical Techniques, 40 CFR Parts 141 and 143 (Final Rule). Federal Register 53 (No. 33), 5142–5147 (Feb. 19, 1988).
Krigbaum, M. (1997). Evaluation of automated solid phase extractions of agrochemicals and industrial organic compounds from drinking water using U.S. EPA Method 525.2. American Environmental Laboratory, 9(4), 12–14.
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