Handbook of Size Exclusion Chromatography and Related ...

2.1 Molecular Weight Grades of PVP Based on KValue
The molecular weights of PVP have traditionally been characterized by the
Fikentscher(2)Kvalue,whichisrelatedtorelativeviscositymeasuredat258Cby
loghrel C ¼
75K2 0
1þ1:5K0C þK0
where K¼1000 K0 and Cis the solution concentration in g/dL. An increase
inh relcorrespondswithanincreaseinKvalue.Table1showsthedependenceofK
valueonh relforgivenvaluesofrelativeviscosity,measuredat1g/dL(or1%wt/
vol). As seen from Table 1, aPVP polymer with arelative viscosity of 2would
have aKvalue of 60 and the polymer would be referred to as aK-60. In industry,
the K value is generally obtained from a table similar to Table 1, with
concentrations specified by the U.S. Pharmacopoea (USP) for the different
molecular weight grades of PVP.The USP specifies that K-30, K-60, or K-90
should be obtained from 1% solutions and K-15 and K-120 should be obtained
from 5and 0.1% solutions, respectively.
The molecular weight ranges of various commercial Kvalue grades of PVP
areshowninTable2.The M wofanunknownPVPsample canbecalculatedfrom
intrinsic viscosity if the Mark–Houwink equation, which correlates intrinsic
viscosity with Mw is known from the literature. The unknown PVP sample should
be similar in branching and polydispersity to the PVP samples from which the
Mark–Houwink equation is derived. Levy and Frank published the following
Mark–Houwink equation in 1955 (3) for unfractionated PVP samples in water at
. Senak et al. published the following Mark–
258C: [h] ¼ 5:65 10 2 M 0:55
w
Houwink equation in 1987 (4) for unfractionated PVP samples in water–methanol
(1:1 vol/vol) with 0.1 M LiNO3 at 258C: [h] ¼ 1:32 10 4 M 0:65
w .
Table 1 K Value vs. Relative Viscosity at 1% Concentration (wt/vol)
K value
Relative
viscosity K value
Relative
viscosity
20 1.120 60 2.031
25 1.175 65 2.258
30 1.243 70 2.527
35 1.325 75 2.846
40 1.423 80 3.225
45 1.539 85 3.678
50 1.677 90 4.219
55 1.839 95 4.870
© 2004 by Marcel Dekker, Inc.