Determination of Semivolatile Organic Compounds in Drinking Water by Solid-Phase Extraction and GC–MS Detection US EPA Method 525.3

Xiaoyan Wang and Don Shelly, UCT, LLC

The US EPA has updated drinking water method 525.2 to 525.3 with the addition of new analytes, preservatives, internal standards, QC criteria, and the option for matrix matched calibrations. A performance based method using SPE cartridge ENVIRO-CLEAN® ECUNI525 (1500 mg unendcapped C18, 83 mL) was approved by EPA and written into the method (Section 11.4). Recovery data using this product were also included in the method (Tables 11 and 12).

1. Cartridge Pre-Rinsing

a) Assemble an extraction manifold system

b) Rinse the bottle holder and cartridge with 5 mL of 1:1 ethyl acetate (EtOAc):dichloromethane (DCM)

c) Draw half through the cartridge, then soak for 1 min

d) Draw remaining solvent through the cartridge

e) Maintain full vacuum for 2 min to dry the cartridge

2. Cartridge Conditioning

a) Add 10 mL of methanol to the cartridge

b) Soak for 1 min

c) Draw through leaving a thin layer of methanol on the cartridge frit

Do not let the cartridge go dry from this point, otherwise recondition

d) Add 10 mL of reagent water to each cartridge

e) Draw through leaving a thin layer of water on the cartridge frit

3. Sample Extraction

a) Ensure that the pH of the preserved sample is ≤ 4

b) Load sample bottle to the bottle holder

c) Adjust vacuum to give a fast drip flow rate. 10 mL/min is an optimum flow rate for high recovery

d) After entire sample has extracted, rinse the sample bottle with 10 mL of reagent water

e) Pass the rinse through the cartridge to remove the sample preservatives

f) Dry the cartridge for 10 min under full vacuum

GC/MS Instrumental Conditions

4. Cartridge Elution

a) Insert 40-mL glass vial in the manifold

b) Rinse bottle, holder, and cartridge with 5 mL of EtOAc

c) Pour the rinsate into the cartridge

d) Draw ½ volume through the cartridge, soak 1 min then draw the remaining through

e) Repeat with 5 mL of DCM

f) Repeat with 5 mL of EtOAc

g) Repeat with 5 mL of DCM

5. Extract Drying

a) Pre-rinse a drying tube containing 10 g of anhydrous sodium sulfate with DCM

b) Quantitatively transfer the eluant through the sodium sulfate tube and collect

c) Rinse the collection tube with 5 mL of DCM

d) Pass DCM through the sodium sulfate and collect

6. Extract Concentration

a) Concentrate the extract to about 0.7 mL (not < 0.5 mL) under a gentle stream of N₂ at 40 °C

b) Transfer the concentrated extract to a 2-mL auto-sampler vial, add internal standards and adjust final volume to 1 mL with EtOAc

c) Samples are ready for GC–MS analysis

Results

Excellent recovery and reproducibility were obtained for all of the 525.3 analytes using UCT's ECUNI525 cartridge (Data presented in Tables 11 and 12 in EPA method 525.3).

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