- What methods are used to determine molecular weights reported in the Sigma-Aldrich Certificate of Analysis?
- What viscometer and viscometry techniques are used to measure viscosity?
- What brands of GPC Laser Light Scattering instruments does Sigma-Aldrich use?
- What is the accuracy (reproducibility) for GPC MALLS/GPC RALLS molecular weight measurement?
- What is the accuracy (reproducibility) for viscosity molecular weight measurement?
- Are there any residual protecting groups left on the final polymer?
- What qualitative and quantitative analytical methods are used to measure the residual protecting groups?
- Does Sigma-Aldrich provide polydispersity profile for polyamino acids?
- What is the general range of polydispersity for polyamino acids listed in the Sigma catalog/website?
What methods are used to determine molecular weights reported in the Sigma-Aldrich Certificate of Analysis?
Two methods are used - (1) Viscosity and (2) either Gel Permeation Chromatography Multi-Angle Laser Light Scattering or Gel Permeation Chromatography Right-Angle Laser Light Scattering (GPC MALLS/GPC RALLS)
Molecular weight data by viscosity is provided for all polyamino acids. GPC MALLS/GPC RALLS molecular weight is provided for only selected polyamino acids. Please see the product listing for information and contact Sigma Technical Services for further details.
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What viscometer and viscometry techniques are used to measure viscosity?
Cannon®, Cannon-Fenske or Ubbelohde viscometers are used to measure viscosity. Contact Sigma Technical Services for details of the technique used for a specific product.
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What brands of GPC Laser Light Scattering instruments does Sigma-Aldrich use?
A Wyatt DAWN EOS GPC MALLS instrument is used for most water-soluble polyamino acids.
A Viscotek™ GPC RALLS instrument is used for measuring very low molecular weight polymers (<5,000 Da) and hydrophobic polyamino acids.
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What is the accuracy (reproducibility) for GPC MALLS/GPC RALLS molecular weight measurement?
Accuracy for GPC MALLS/GPC RALLS molecular weight measurement is ± 5 to 10% (within manufacturer’s suggested range).
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What is the accuracy (reproducibility) for viscosity molecular weight measurement?
Accuracy for viscosity molecular weight measurement is ± 5 to 10% (within experimental error).
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Are there any residual protecting groups left on the final polymer?
Yes, approximately 1% or less may be present. If the customer requires a lower content of residual protecting group, Sigma-Aldrich can develop a custom process to decrease the amount of residual protecting group present in the final product.
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What qualitative and quantitative analytical methods are used to measure the residual protecting groups?
UV spectrophotometry at 250 - 300 nm is used for qualitative testing and proton NMR spectroscopy is used for quantitative testing.
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Does Sigma-Aldrich provide polydispersity profile for polyamino acids?
Polydispersity is not routinely measured on polyamino acids. Upon customer request, Sigma-Aldrich can provide polydispersity profiles for any water-soluble homopolymers with >5,000 Da molecular weight.
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What is the general range of polydispersity for polyamino acids listed in the Sigma catalog/website?
The general range of polydispersity for our polyamino acids is 1.1 to 1.5. Generally the higher molecular weights give lower polydispersity, whereas lower molecular weights give higher polydispersity. This is a general rule of thumb but it is not always true for every product.
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