Cation-SR is a poly(styrenedivinylbenzene) copolymer that has been modified with sulfonic acid. Note that Cation-SR is not bonded to silica but is a 100% copolymeric particle that is spherical, porous and cross-linked. The functional group imparts selectivity for cationic analytes, such as primary, secondary and tertiary amines.
| Sorbent: |
Poly(styrenedivinylbenzene) |
| Functional Group: |
Benzene sulfonic acid |
| Ionic Form: |
Hydrogen |
| Surface Area: |
350 m²/g |
| Particle Size: |
16 µm (avg. diameter) |
| Capacity: |
1.1 meq/g Cu+2, 0.4 meq/47 mm disk (nominal) |
| Pore Size: |
80 Å (avg.) |
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Product Usage
Sample Preparation
Adjust the sample pH as necessary to ensure that the analytes are ionic. A general guideline is to lower the sample pH at least two units below the pKa of the analytes being extracted. Next dilute the sample with reagent water as needed to reduce the ionic strength to < 0.1M.
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 -15 mL (for 47 mm disk) acetone. Apply vacuum and air dry the disk.
- Wash the disk with 10-15 mL methanol and allow the disk to soak for 30-60 seconds. Apply vacuum briefly, leaving 3-5 mm of methanol above the surface of the disk.
- Add 10-15 mL of reagent water, followed by 10-15 mL of 50% (v/v) nitric acid, and a final 10-15 mL of reagent water (use 2 successive 20 mL aliquots of acetone if the sample matrix is non-aqueous).
The disk is now conditioned and 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 1 Liter of DI water at 25oC at 20 in Hg of vacuum (47 mm disk) will extract in less than 10 minutes.
Flow rate is dependent on vacuum source and the particulate content of the sample. Empore™ 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 by applying the 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 10-15 mL (47 mm disk) is suggested. Elution is often encouraged by the selection of a high selectivity counterion, high ionic strength, and a pH adjusted to 1-2 units above than the pKa of the analytes extracted. An effective elution solvent for metals is 50% (v/v) nitric acid. An effective elution solvent for non-metals is 0.1N sodium hydroxide. Very strong bases such as quaternary amines may be difficult to elute from the cation 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.
