Polymer Standards Handling
Storage of polymer standards
Store the standards in a dry, dark, cool area; e.g. a refrigerator (4°C), and tightly recapped. This keeps excessive moisture away and increases the standard shelf life.
Do not store standards exposed to direct sunlight (windowsill or shelf near windows), to prevent sample degradation over time. This condition is critical to Poly(isoprene), Poly(butadiene) and other temperature and/or light sensitive polymers.
Use only freshly prepared solutions and use them up within two days. Solutions may be stored in the refrigerator temporarily. Do not freeze standards in solution; freezing can destroy the sample.
Samples preparation for GPC/SEC analysis
- Prepare fresh standard solutions to assure accurate concentrations. Precise concentration values are required when using a light scattering, viscometry or Triple detection system.
- Select the appropriate clean dissolution container (autosampler vial, bottle, flask, etc.).
- Add an appropriate quantity of sample using an analytical balance. Start with the concentrations provided in table 2 as guideline. The moisture content should be determined before starting any measurements. Dry the polymer if necessary. Its variability depends on several parameters (e.g. surface, molecular weight, sample preparation, storage conditions, etc.).
- Standard mixtures: It is possible to dissolve up to four standards of the same type in a given dissolution container. If you make your mixture, the individual standards molecular weight must be separated by orders of magnitude to prevent coelution; e.g. Poly(styrene): 5 000 Da, 50 000 Da, 500 000 Da. PSS offers pre-made mixtures or kits that prevent co-elution.
When using a viscometer or light scattering detector, the standard mixture peaks must reach the baseline between each standard injected in order for the standard to be used in a calibration curve. - Select your working concentration based on detection type and number of columns in use.
- Add the solvent volume accurately.
If you use an internal standard for flow rate monitoring, mix it with a fraction of mobile phase in a separate container. Use the marked solvent to prepare your standards. Do not add it into the general solvent bottle. The internal standard should be monodisperse, and elute after the separation limit.
Recommended Sample Concentration
| Molecular Weight Range [Da] | Concentration [g/l] or [mg/ml] |
|---|---|
| 100 - 10 000 | 1 to 2 |
| 10 000 - 100 000 | 1 to 2 |
| 100 000 - 500 000 | 1 to 2 |
| 500 000 - 1 000 000 | 1 to 2 |
| 1 000 000 and above | 0.5 or less |
| broad standards usually | 4.0 - 5.0 mg/ml |
- Close or seal the dissolution container and let sit at room temperature for 24 hours or overnight for complete dissolution.
Let polymers of Mw < 200 000 Da, sit for 3-4 hours. Ultra high molecular weight standards and samples > 2 000 000 Da may take from 1-3 days to dissolve completely. - Gently swirl the vials for a homogeneous solution.
Do not use stir bars, ultrasonic baths, microwave heating or harsh shaking as this can cause sample degradation. - Inject each solution separately. Start with the guideline below to develop your optimum injection volume.
Recommended Injection Volume
| Number of columns (length 30 cm) | Guideline injection volume [µl] |
|---|---|
| 4 - 5 and more | 200 to 250 |
| 3 | 100 |
| 2 | 50 |
| 1 | 20 |
- Ultra high molecular weight samples (Mw > 1 000 000 Da) elute best in low concentrations, through columns of large particle (10µm, 20µm) and pore sizes. Work at reduced flow rates (0.5 – 0.3 ml/min) and if necessary increased injection volume. This reduces the probability of sample degradation.
Example: Inject 100 µl of a solution of 0.1 g/l instead of 20 µl of a solution of 0.5 g/l. - Use the measured Mp values of the standards to construct a calibration curve.