Approved EPA Methods
| Safe Drinking Water Act |
548.1 and 552.1 |
Specifications
| Sorbent |
Poly(styrenedivinylbenzene) |
| Functional Group |
Quaternary Ammonium |
| Ionic Form |
Chloride |
| Surface Area |
350 m2/g |
| Particle Size |
12 µm (avg. diameter) |
| Pore Size |
80 Å (avg.) |
Product Usage
Sample Preparation
Adjust the sample pH as necessary to ensure that the analytes are ionic. A general guideline is to raise the sample pH at least two units above the pKa of the analytes being extracted. Next dilute the sample with reagent water as needed to reduce the ionic strength to <0.1M.
Note: Avoid using acids with highly selective anions such as sulfate to adjust pH. Lower selectivity acids such as hydrochloric acid are recommended for pH adjustments.
Extraction Disk Conditioning
Disk conditioning is critical for a successful extraction. Conditioning prepares the sorbent to interact efficiently with the sample matrix.
Failure to condition the Extraction Disk properly will result in erratic and low recoveries.
- Wet the disk with a few mL of acetone and assemble the filtration apparatus. Wash the disk and system with 10 – 15mL (for 47mm disk) acetone. Apply vacuum and air dry the disk.
- Wash the disk with 10 – 15mL methanol and allow the disk to soak for 30 – 60 seconds. Apply vacuum briefly, leaving 3 – 5mm of methanol above the surface of the disk.
- Add 10 – 15mL of reagent water, followed by 10 -15mL of 1M sodium hydroxide, and a final 10 – 15mL of reagent water.
The disk is now ready to extract the sample.
Note: If the disk becomes dry while conditioning, repeat the conditioning steps starting with the methanol step.
Extraction Considerations
Add the sample and apply vacuum (<20 in Hg, 0.68 bar). Flow rates will vary. Typically one liter of DI water at 25°C at 20 in Hg of vacuum (47mm disk) will extract in less than 10 minutes.
Note: Due to the nature of the ion exchange reaction, slower flow rates may be desirable to allow the reaction kinetics adequate time to occur. Evaluating recoveries at varying flow rates of sample extraction and elution allows the determination of optimal sample processing time for a given analyte and sample matrix.
Flow rate is dependent on vacuum source and the particulate content of the sample. 3M Filter Aid 400 and/or other prefiltration may be helpful if the sample contains excessive amounts of particulates. Remove as much of the residual water as possible from the disk prior to the elution step by applying vacuum to dry the disk for 5 – 10 minutes.
Optional: An intermediate wash with methanol or another organic solvent will remove neutral organics. Electrostatic forces will not be disturbed by this step.
Elution Requirements
Eluting twice with 10 – 15mL (47mm disk) is suggested. Elution is often improved by the selection of a high selectivity counterion, high ionic strength, and pH adjusted to 1 – 2 units lower than the pKa of the analytes extracted. Highly selective ions such as sulfonic acids may be difficult to elute form anion exchange disks.
If the disk dries prior to elution, pre-wetting with a minimum amount of methanol is necessary to re-establish surface tension. For example, to elute with an aqueous buffer, simply wet the disk with enough methanol to cover the surface, then add the buffer. Another option is to elute with an acidic methanol solution.