Empore™ Chelating Disks provide a way to selectively remove multivalent metal cations from solutions. This selectivity can be used to concentrate metals from a sample for analysis or to isolate and remove metal interferences from a complex organic or inorganic sample matrix. In the latter case, the purified filtrate is ready for use.
The chelating disk has an affinity for multivalent (primarily 2+ and 3+) transition elements. The functional group exhibits differing ionic charges depending on the pH of the solution.
- At pH 2, the carboxylate groups are neutral and the nitrogen has a net positive charge. This allows the sorbent to function as a weak anion exchanger.
- Increasing the pH ionizes the carboxylate groups and at pH =5, both are negatively charged.
- As the pH approaches neutral, the sorbent functions as a cation exchanger or a chelating resin.
| Sorbent: |
Poly(Styrene divinylbenzene) |
| Functional Group: |
Sodium salt of iminodiacetic acid |
| Particle size |
10 µ |
| pH stability |
1 to 14 under normal use conditions |
| Capacity Cu+2 |
>1.9 meq/g @ pH 5 |
| Selectivity in ammonium acetate buffer |
- Cu>Cd>Co>Mn>Ba>Ca>Sr
- Zn>Al>Cr>Sn
- Pb>Fe>Ni>Mg
|
Product Usage
For many applications, the Empore™ Chelating Disk can be used directly by wetting with only water. For trace (ppb) metal analysis, the disk should be conditioned.
Note: Because of the adsorptive properties of the disk, handling with non-metallic instruments is recommended.
Extraction Disk Conditioning
Prewetting the chelating disk with an organic solvent such as methanol is NOT recommended, as this will not improve flow rate but will cause the disk to wrinkle.
- Wet the disk with 20 mL of reagent water under vacuum.
- Wash the disk with 20 mL of 3.0M nitric acid or 3.0M hydrochloric acid followed by two 50 mL water washes. Let the disk go dry between each wash.
- To put the disk in the ammonium form (its most active form), wash with 50 mL of 0.1M ammonium acetate buffer at pH 5.3 followed by several reagent water washes.
The disk is now conditioned and ready to extract the sample.
Extraction Considerations
Add the sample and apply vacuum (< 20 in Hg, 0.68 bar). Flow rates will vary. Typically, using a 47 mm disk, 1 Liter DI water at 25oC and 20 in Hg 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, before the elution step, by applying the vacuum to dry the disk for 5- 20 minutes.
Elution Requirements
Elution of metals from the chelating disk is achieved with strong acids such as 3.0M nitric acid or 3.0M hydrochloric acid. Most metals can be quantitatively recovered by eluting twice with 10 mL (47 mm disk) of 3.0M nitric acid or 3.0M hydrochloric acid and combining the eluates.
A few metals (e.g., chromium) may be difficult to elute, particularly if left on the membrane for several hours.
Detailed Product Instructions (PDF, 20 Kb)
