Linear column

The linear column (PSS SDV 5 /mm linear) has a wider molar mass fractionation range while keeping the analysis time roughly the same. Therefore the slope of the calibration curve is much steeper and the resolution will be poorer in this case. The second column with a single pore size (PSS SDV 5 /mm 1000 A) separates only below 50,000 Da, but does this very efficiently in the same time. 

FIGURE 10.8 Analysis of sulfonated polystyrenes on SynChropak GPC Linear. Column 250 X 4.6 mm i.d. Flow rate 0.5 ml/min. Mobile phase 0.1 M sodium sulfate, pH 7. (From MICRA Scientific, Inc., with permission.)... 

Molar Mass Interval. GPC columns are offered for different molar mass intervals for larger intervals it is possible to combine some columns of different pore size types or to combine a few so-called mixed bed or linear columns. Both possibilities have their own special advantages and disadvantages mixed bed columns with a linear separation range of more than four molar mass decades are suitable to quickly get an overall view of a new sample, whereas a column set, carefully selected from different pore size types, often has a much better separation efficiency in a limited mass interval (for details, see Sections in and IV). 

Two linear columns from Showa Denko, Shodex SB-806M and Shodex SB-806MHQ, and two linear columns from TosoHaas, TSK GM-PWxl and TSK GM-PW, were evaluated. Prior to the evaluation, the number of theoretical plates for Shodex SB-806MHQ, SB-806M, PWxl, and PW was determined to be 15,100, 15,700, 11,390, and 4710, respectively, as per manufacturer inspection. The lower plate count of the TSK PW column is due to the larger particle size of this column. Two mobile phases, water with 0.1 M LiNOi and 50 50 methanol/water (v/v) with 0.1 M LiNOi, were used for each of the four columns. These four columns were new and only PEO and PVP were analyzed with these columns in this study. Waters Ultrahydrogel columns have also been used in this laboratory. However, Ultrahydrogel columns are exactly the same as the TSK GM-PWxl columns based on the calibrations curves supplied by the manufacturers and by the pyrolysis GC data discussed later. 

Table 17.2 shows good agreement between the retention times from the TSK PEO standards analyzed in groups of two or three and the retention times of the TSK PEO standards analyzed individually. ASTM-D5296 requires that for standards to be run as a group, the molecular weight must differ by a factor of 10 (11). The results in Table 17.2 showed that a difference in molecular weight by a factor of 6 is adequate to obtain consistent flow times for standards for the modem linear columns. 

The M of a PVP K-90 sample and a PVP K-30 sample were determined with four linear columns with four sets of PEO standards to study the dependency of M of PVP on the column and the PEO standard used. M for PVP K-90 calculated from the TSK GM-PW column are in general higher than the other three columns in this study for all four sets of PEO standards. This is discussed further in Section III,G,2. Similar to the case of the M of NIST PEO standards calculated from PL PEO standards, M for PVP K-30 calculated from the PL PEO standards are lower than M from TSK, APSC, and PSS PEO standards, no matter which column or mobile phase is used. However, M for PVP K-... 

TABLE 17.7 Coefficient of Determination (R ) for Linear Calibration Curves for Four Linear Columns and Four Sets of PEO Standards... 

Ra and Rb in Table 17.8 are less than 1.7 because the molecular weights of the standards differ by a factor less than 10. They will be used later to compare the separation efficiency in the high molecular weight range and low molecular weight range for these four linear columns. 

TABLE 17.8 Separation Efficiency of Four Linear Columns in Water and Water/Methanol for Polyethylene Oxide Standards... 

In summary, methanol as a mobile-phase modifier has a significant effect on the separation of PVP in aqueous SEC with these four linear columns. The best separation of all PVP grades can be achieved with the SB-806M column in 50 50 water/methanol with 0.1 M lithium nitrate. It is interesting to note that despite the improvements reported by the manufacturers for the newer columns (SB-806MHQ and PWxl), the newer columns do not necessarily perform better than the older columns (SB-806 and PW) for aqueous SEC of PVP. 

Retention time of major peaks (min) Identification TSK GM-PWxl G3000 TSK GM-PW Ultrahydrogel linear column Shodex OH-pak, KB-80M... 

For all four sets of PEO standards the coefficient of determination (R ) for the linear calibration curves for the four linear columns in water and in water/methanol are better than 0.99, except for the PL PEO standards and the TSK GM-PWxl column in water/methanol. The coefficient of determination for the TSK GM-PWxl column in general is not as good as the other three linear columns. The coefficient of determination for the TSK PEO standards showed the least dependency on columns and mobile phases. The TSK GM-PWxl column has a lower exclusion limit in the high molecular weight range than TSK GM-PW, Shodex SB-806, and SB-806MHQ columns. 

FIGURE 21.2 An example of a possible dislocation due to a mismatch pore sizes in linear columns. 

In conclusion one can say that SEC is a very powerful method for polymer characterization, especially in combination with other composition sensitive or absolute calibration methods. A big advantage is also that the sample amount is fairly small, typically 10 mg. For more complex polymers, such as polyelectrolytes, enthalpic effects often become dominant and also for rather high molecular weight polymers chromatographic methods such as field-flow fraction (FFF) techniques might be more suitable. For fast routine measurements linear columns are often used. 

Atwood, J. L., Barbour, L. J., Raston, C. L., Supramolecular organization of C60 into linear columns of five fold, Z-shaped strands. Cryst. Growth Des. 2002, 2, 3-6. 

Polyacrylamide hydrogel (linear) column, 10 pm ethylenechlorotrifluoro-ethylene 10 mM Tris, 100 mMH3P04 or water-acetonitrile (10 90) with TFA (0.15%) 420 mm x 100 pm i.d. 270 mm packed length... 

Molecular weights were obtained by GPC in dichloromethane (1 mL/min) using a Waters pump model 6000, an injector (Rheodyne) and a refractive index detector (RID-6A Shimadzu), equipped with a PL gel 5)iim mixed-C linear column. The system was calibrated using polystyrene standards with low polydispersity. 

Note that for so-called linear column separations, the denominator d( ogioM)ldV is just a constant and, therefore, the differential weight fraction distribution will appear as a reflection (small mass first, from ieft to right) of the DRI signai. In general, column separations are not linear, so the DRI signal is not a good representation of the mass-elution distribution. 

All of the currently used porous packing materials have a three-dimensional network structure, effectively giving rise to a pore size distribution. In these separating media, the dependence of 7 on A will be less sharp compared with the one in Fig. 3. It is desired by chromatographers that the retention time is a linear function of log M. Because the retention time is a linear function of K, the plot of K needs to be a linear function of log M in as broad a range of MWs as possible. A naturally occurring pore size distribution is not sufficient to cause the desired linearity. Therefore, mixed-bed columns, packed with porous materials of different pore-size-distribution ranges, have been developed and used broadly as linear columns. 

Size-exclusion chromatography of PVP K-15, K-30, K-60, K-90, and K-120 using linear aqueous columns such as the Showa Denko Shodex OH pack, Toyo Soda TSK-PW, and Waters Ultrahydrogel has been reported in 1995 by Wu et al. [9]. Using single linear columns also greatly reduces analysis time and solvent consumption, making SEC a practical method for quality assurance. A comparison of four commercial linear aqueous columns and four sets of commercial PEO standards for SEC of PVP K-15, K-... 

Finally, the following SEC columns, which have been introduced in recent years, have been demonstrated by the vendors to be successful with PVP Jordi DVB Glucose BR linear column [in dimethyl sulfoxide (DMSO)], PL aquagel-OH column (in 0.1M-0.3M salt-buffer with 20% methanol) PSS Suprema column (in O.IM Tris pH 7 buffer), and PSS SDV column (in DMAC, 0.1% LiBr) [11-13]. 

The N-bonded silanetriol (2,4,6-Me3C6H2)N(SiMe3)Si(OH)3 [26] organizes itself in a tubular form which is made up of four linear columns. Further, these columns are displaced with respect to each other by a 90° rotational relationship. As a result of this arrangement there is an interesting formation of silanetriol tubes in the crystal which contain a hydrophilic interior and a hydrophobic exterior. 

The MWDs of the obtained samples were determined by SEC on a Knauer setup with a linear column (Phenomenex, Linear 2). A R1 Detector K-2301 differential refractometer and UV Detector K-2501 were used as the detectors for PMMA and polystyrene samples respectively. Chloroform was used as the eluent. The columns were calibrated using standard PMMA and polystyrene samples, obtained from Waters. The ChromGate software was implemented for interpretation of SEC data. 

Molecular Weight Molecular weight of the polymers was determined from GPC (Waters 244) with Ultrast5Tagel 500 A-linear-columns. The measurement was conducted using an RI detector in THF at a flow rate of 1.0 ml/min at 281C. PS was used as the standard for calibration. 

Alternative screening techniques may reduce moire and enhance image quality. One alternative is stochastic screening, also known as random-dot or Irequency-modulated (FM) screening. This method does not rely on linear columns of dots to produce a completed image. Instead, the image is broken into varying concentrations of randomly placed, identically sized dots. 

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