Editing Molecular mass (section)

=== Hydrodynamic methods ===
To a first approximation, the basis for determination of molecular mass according to [[Mark–Houwink equation|Mark–Houwink relations]]<ref>Paul, Hiemenz C., and Lodge P. Timothy. Polymer Chemistry. Second ed. Boca Raton: CRC P, 2007. 336, 338–339.</ref> is the fact that the [[intrinsic viscosity]] of [[Solution (chemistry)|solution]]s (or [[suspension (chemistry)|suspensions]]) of macromolecules depends on volumetric proportion of the dispersed particles in a particular solvent. Specifically, the hydrodynamic size as related to molecular mass depends on a conversion factor, describing the shape of a particular molecule. This allows the apparent molecular mass to be described from a range of techniques sensitive to hydrodynamic effects, including [[dynamic light scattering|DLS]], [[size exclusion chromatography|SEC]] (also known as [[Gel permeation chromatography|GPC]] when the eluent is an organic solvent), [[viscometry]], and diffusion ordered [[nuclear magnetic resonance spectroscopy]] (DOSY).<ref>{{cite journal|author1=Johnson Jr., C. S. |journal=[[Progress in Nuclear Magnetic Resonance Spectroscopy]]|year=1999| volume=34|pages=203–256|title=Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications |issue=3–4|doi=10.1016/S0079-6565(99)00003-5|bibcode=1999PNMRS..34..203J }}</ref> The apparent [[Hydrodynamic radius|hydrodynamic size]] can then be used to approximate molecular mass using a series of macromolecule-specific standards.<ref>{{cite journal|author1=Neufeld, R. |author2=Stalke, D. |journal=[[Chem. Sci.]]|year=2015| volume=6|pages=3354–3364|title=Accurate Molecular Weight Determination of Small Molecules via DOSY-NMR by Using External Calibration Curves with Normalized Diffusion Coefficients |issue=6 |doi=10.1039/C5SC00670H|doi-access=free|url=http://goedoc.uni-goettingen.de/goescholar/bitstream/handle/1/11975/c5sc00670h.pdf?sequence=1 |pmid=29142693 |pmc=5656982}}</ref> As this requires calibration, it's frequently described as a "relative" molecular mass determination method.