Polystyrene molecular weight standards

Small particle size resins provide higher resolution, as demonstrated in Fig. 4.41. Low molecular weight polystyrene standards are better separated on a GIOOOHxl column packed with 5 /u,m resin than a GlOOOHg column packed with 10 /Ltm resin when compared in the same analysis time. Therefore, smaller particle size resins generally attain a better required resolution in a shorter time. In this context, SuperH columns are best, and Hhr and Hxl columns are second best. Most analyses have been carried out on these three series of H type columns. However, the performance of columns packed with smaller particle size resins is susceptible to some experimental conditions such as the sample concentration of solution, injection volume, and detector cell volume. They must be kept as low as possible to obtain the maximum resolution. Chain scissions of polymer molecules are also easier to occur in columns packed with smaller particle size resins. The flow rate should be kept low in order to prevent this problem, particularly in the analyses of high molecular weight polymers. 

Traditionally, column efficiency or plate counts in column chromatography were used to quantify how well a column was performing. This does not tell the entire story for GPC, however, because the ability of a column set to separate peaks is dependent on the molecular weight of the molecules one is trying to separate. We, therefore, chose both column efficiency and a parameter that we simply refer to as D a, where Di is the slope of the relationship between the log of the molecular weight of the narrow molecular weight polystyrene standards and the elution volume, and tris simply the band-broadening parameter (4), i.e., the square root of the peak variance. 

Calibration of Gel Permeation Chromatograph Polystyrene Calibration. A plot of molecular size in (S) versus elution volume for polysty-rene standards in dichloromethane showed deviation from linearity at about 2,200 which may be attributed to Imperfect column resolution, peak broadening, axial dispersion and skewing. The extensive tailing of the chromatograms of high molecular weight polystyrene standards observed in dichloromethane has also been reported in the literature (23-26). 

Dead Volume. The dead volume difference between the viscometer and DRI must be accounted for. Otherwise systematic errors in Mark-Houwink parameters K and u can occur. In the previous paper (16), a method developed by Lesec and co-workers (38) based on injecting a known amount of a very high molecular weight polystyrene standard onto low porosity columns was used. From the viscometer and DRI chromatograms, the apparent intrinsic viscosity [h] was plotted against retention volume V. A series of [n] vs. V plots are then constructed assuming a range of dead volume, AV. 

Molecular weights of the polystyrene were determined using a Polymer Laboratories gel permeation chromatograph (GPC) with tetrahydrofuran (THF) as the mobile phase the values reported are relative to narrow molecular-weight polystyrene standards. The polystyrene and polyethylene were separated by dissolving the blends in xylenes at 120 °C and precipitating the polyethylene in a 2 1 (vol/vol) mixture of acetone and cyclohexane. After filtration, polystyrene was isolated from the resulting solution by rotary evaporation. 

The application of the silicas shown in Figure 5 in SEC is demonstrated in Figure 6, in which six narrow molecular weight polystyrene standards ranging... 

MolGCUlar WGight. The molecular weight distribution of cellulose esters is normally determined by gel-permeation chromatography (GPC) (126) in which the ester, dissolved in a suitable solvent, is eluted through a column of porous cross-linked polystyrene. The elution profiles are compared to narrow molecular weight polystyrene standards to obtain the molecular weight or DP distribution. Other... 

Molecular weights were determined by gel permeation chromatography (GPC) using a Waters HPLC system equipped with noodel 510 pump. Waters model 717 autosampler, model 410 refractive index detector, and model T-50/T-60 detector from Viscotek Corporation with 500, 10, 10 and 10 A ultrastyragel columns in series. Trisec GPC software version 3 was used for calculations. Chloroform was used as the eluent at a flow rate of 1.0 mL per minute. Sanq>le concentrations of 0.2 % wt/vol and injection volumes of 100 )XL were used. Molecular weights were determined based on a conventional calibration curve generate by narrow molecular weight polystyrene standards obtained from Aldrich chemical conq>any. 

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