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- Posts: 2
- Joined: Fri Mar 03, 2023 1:30 pm
- Location: Ukraine
We are conducting molecular weight control in accordance with the United States Pharmacopoeia monograph. We used Dextran standards ranging from 5000 to 410000 Da, a refractive index detector, and two columns: 7.8-mm × 30-cm; packing L39 with pore sizes of 1000 and 120 Å, respectively.
My calibration curve, based on retention time by GPC/SEC, is perfect with an R2 = 0.9999 when using my standards, which already have known Mw values. However, when we calculate the Mw of our samples, the results do not meet the requirements and are almost twice as high. We have noticed that when we change the Mark-Houwink constants (used for the viscometric detector), the results change significantly. But I know that we don`t need this parameters in our calculation because we don`t have viscosity.
Could it be possible that the detector was incorrectly selected during the program installation, as the change in Mark-Houwink constants critically affects the result? What could we be doing wrong?"