Calibration weight distribution standards

Determining Calibration Curves frcm Polydisperse Samples. In conventional SEC interpretation, narrow molecular weight distribution standards are needed for calibration purposes. Nonlinear regression has enabled polydisperse scimples to be used. A variety of methods... 

Nonlinear regression enables broad molecular weight distribution standards to be used for SBC calibration and permits simultaneous resolution correction euid calibration. Furthermore, it greatly increases the variety of equations 4iich can be fit to calibration curves, detector linearity data and chromatogreun shapes. 

Calibration of GPC-SEC with Narrow Molecular-Weight Distribution Standards... 

To determine the interdetector delay volume for a viscometer, a broad molecular weight distribution standard can be injected and a Mark-Houwink plot, that is, log [t ] versus log M, generated using universal calibration. The interdetector volume is adjusted until the expected Mark-Houwink exponent is obtained (36). 

With a light-scattering detector, a log M versus elution volume calibration curve is constructed from a series of narrow molecular weight distribution polymer standards. A broad molecular weight distribution standard is then injected, and an iterative procedure finds the interdetector volume that superimposes the broad MWD standard calibration curve onto the one established by the narrow standards (38). 

Noting GPC is a relative molecular weight method, such instrumentation needs to be calibrated. Narrow molecular weight distribution, anionically synthesized polystyrenes are used most often for the purpose. Other polymers used for calibration include poly(methyl methacrylate), polyisoprene, polybutadiene, poly(ethylene oxide), and the sodium salt of poly(methacrylic acid). Molecular weight ranges available start at low oligomers of only a few hundred g/mol, up to 20,000,000 g/mol. In aU cases, use of narrow molecular weight distribution standards is preferred. 

Determinarion of MW and MWD by SEC using commercial narrow molecular weight distribution polystyrene as calibration standards is an ASTM-D5296 standard method for polystyrene (11). However, no data on precision are included in the 1997 edition of the ASTM method. In the ASTM-D3536 method for gel-permeation chromatography from seven replicates, the M of a polystyrene is 263,000 30,000 (11.4%) for a single determination within the 95% confidence level (12). A relative standard deviation of 3.9% was reported for a cooperative determination of of polystyrene by SEC (7). In another cooperative study, a 11.3% relative standard deviation in M, of polystyrene by GPC was reported (13). 

The significance of knowing the K and a values of fully hydrolyzed PVA is that molecular weight distribution data can be directly calculated using two methodologies. The first is the Mark-Houwink method, which requires prior knowledge of K and a values for fully hydrolyzed PVA and calibration standards such as PEG, PEO, or PSC. The second method is the intrinsic viscosity method. This method utilizes a simple ratio of the concentration signal to the specific... 

Previous methods of molecular weight calibration using broad MWD standards were of three basic types. Those which employ a broad MWD standard with known molecular weight distribution... 

The peak position and universal calibration methods rely on peak position calibration with known polymers of narrow molecular weight distribution. Several other calibration procedures requiring only a single broad moleculau weight standard have been proposed [77,439]. These procedures are quite c< plex and have a major drawback in that, unlike the peak position methods, instrumental peak broadening must be accounted for correctly if accurate results are to be obtained. 

Shimadzu Xex = 486nm, A,em = 516 nm) with a chart recorder (Fisher Recordall, Series 5000, Springfield, NJ). F-PHEA concentrations in perfusate were determined by area comparison of the eluted curves to that of the standard. Curves of logMW vs. elution volume, Ve, were constructed for each column using the integral-MWD method as described previously (9). Molecular weight distributions of absorbed material were determined from the calibration curves and the sample s chromatograph by curve summation (9). 

Standard Test Method for Molecular Weight Averages and Molecular Weight Distribution of Certain Polymers by Liquid Size-Exclusion Chromatography (Gel Permeation Chromatograph -GPC) Using Universal Calibration" ASTM D 3593 80, Annual Book of ASTM Standards, ASTM, Philadelphia, PA, revised annually. 

The polymerization was carried out in THF under the conditions of high vacuum or argon atmosphere with a catalytic amount of alkyllithium as an initiator. Anionic polymerization of 3a with n-BuLi in THF followed by quenching with ethanol afforded polymer 6 in 56 % yield. The molecular weight distribution of the polymer was determined by gel permeation chromatography (GPC), calibrated by polystyrene standards, with chlorofrom as eluent Mn = 6.1xl0"4, Mw/Mn = 1.3. 

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