Calculation of molecular weight

For the calculation of molecular weight using Eq. (4), R should be measured accurately, which can be done with a pressure drop-residence time method described in Tijssen et al. (7). 

Non-ideal behavior in SEC, due to the contribution of nonsize effects to retention, particularly in the case of the separation of polyelectrolytes in aqueous SEC, can render erroneous the calculation of molecular weight and molecular weight... 

TABLE 6.2. Data for Calculation of Molecular Weights of Various Types of Fragment Ions... 

In the calculation of molecular weight, grams/mole, grams would be too low, so the effect would be a lower MW than expected. 

In the calculation of molecular weight, g/mole, there would be less HA available than expected. Therefore, in the titration against NaOH, it would take less NaOH than expected to reach the equivalence point. This error would cause a larger MW than expected, because the denominator (moles) would be smaller. 

The two alternative methods to solve eq. 3.41 for calculation of Molecular weight are one due to Debye and other due to Zimm. 

Tompa, H., The Calculation of Molecular-Weight Distributions from Kinetic Schemes, Chap. 7 in Comprehensive Chemical Kinetics, Vol. 14A, C. H. Bamford and C. F. H. Tipper, eds., American Elsevier, New York, 1976. 

Since the intrinsic viscosity depends not only on the size of the macromolecule but also on its shape, on the solvent, and on the temperature, there is no simple relationship for the direct calculation of molecular weights from viscosity measurements. However, the Mark-Houwink-Kuhn equation gives a general description of how the molecular weight can be calculated from the intrinsic viscosity ... 

Student would think they had 25.000 grams when there were actually 25.010 grams. In the calculation of molecular weight (grams/mole), the grams would be too low, so the effect would be a lower MW than expected. 1 point for correct explanation. 

GPC Parameters for Calculation of Molecular Weight Averages and Distribution... 

Calibration is required to convert measurements of scattered light intensity from arbitrary to absolute values, an essential step in the calculation of molecular weight. Fortunately, because the calibration constant of most photometers remains stable for long periods of time, the calibration procedure need be carried out only infrequently. Should it need to be calibrated, the procedure described in ASTM D4001-93 or that of the instrument vendor should be followed. 

The calculation of the gel point or the molecular weight distribution becomes difficult if the functional groups in monomers differ in reactivity (26, 27). Polycondensation of glycerol with symmetrical dibasic acid or of an unsymmetrical dibasic acid with symmetrical tribasic alcohol may serve as examples. The reaction probabilities of various functional group , necessary for the calculation of molecular weight distributions and gel points, have to be determined either from complete chemical analysis or from the kinetics of the respective reactions. 

This equation provides an accurate calculation of molecular weight and is applicable to macromolecules such as proteins and nucleic acids. However, its usefulness is limited because diffusion coefficients are difficult to measure and are not readily available in the literature. 

As now all the tools needed are available, the third field of investigation in PDC can be discussed, namely that of the calculation of molecular weight distributions of very narrowly distributed samples as obtained, e.g., in the anionic polymerization of styrene. 

Perminova, I. V., Frimmel, F. H., Kovalevskii, D. V., Abbt-Braun, G, Kudryavtsev, A. V., and Hesse, S. (1998). Development of predictive model for calculation of molecular weight of humic substances. Water Res. 32, 872-881. 

The eluate is freeze dried to give a light powdery product. Yield 18-20 mg per 350 mg dry venom. Calculation of molecular weight of the protein based on the amino acid composition gives a value of 30.000 which is in a very good agreement with that obtained by physical methods. 

For the calculation of molecular weights in CSTR emulsion reactors, a vsefnl classification comes to mind. This includes those monomer systems whose molecular weight and branching development depends on particle size and those that do not. Styrene falls into the former class and vinyl chloride and vinyl acetate into the latter class. Thus, in vinyl chloride emulsion polymerization where LCB is neglected, the instantaneous molecular weight distribution is given by... 

Reuter J. H. and Perdue E. M. (1981) Calculation of molecular weights of humic substances from colligative data application to aquatic humus and its molecular size fractions. Geochim. Cosmochim. Acta 45, 2017-2022. 

The calculation of molecular weights and molecular weight distributions for three-dimensional polymers is considerably more difficult and complicated than that for linear polymers. Flory s calculation of the... 

For calculation of molecular weights from intrinsic viscosities we used the Staudinger equation (35). On account of the high molecular weights of emulsion polymers we exceeded the range for which the constants were determined to a considerable amount. 

The necessary conditions for application of the universal calibration method and for calculation of molecular weights through Eq. (6) is the knowledge of the [r]]i values, which are obtained from the Mark-Houwink equations when the pertinent values of K and a constants are known. An alternative way is to make a continuous measurement of [t]]i at the different elution volumes with an on-line viscometer detector coupled to the usual concentration detector system. 

To illustrate the calculation of molecular weight averages using moment equations, let us consider a free radical polymerization of vinyl monomers. Table 3 shows the kinetic equations based on the kinetic... 

Figure 39-11. Data for the calculation of molecular weight by conventional sedimentation equilibrium.

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