Calibration with weighting

A 10-mL volumetric pipet was calibrated following the procedure just outlined, using a balance calibrated with brass weights having a density of 8.40 g/cm. At 25 °C the pipet was found to dispense 9.9736 g of water. What is the actual volume dispensed by the pipet ... 

The viscosity average molecular weight is not an absolute value, but a relative molecular weight based on prior calibration with known molecular weights for the same polymer-solvent-temperature conditions. The parameter a depends on all three of these it is called the Mark-Houwink exponent, and tables of experimental values are available for different systems. 

Since viscometer drainage times are typically on the order of a few hundred seconds, intrinsic viscosity experiments provide a rapid method for evaluating the molecular weight of a polymer. A limitation of the method is that the Mark-Houwink coefficients must be established for the particular system under consideration by calibration with samples of known molecular weight. The speed with which intrinsic viscosity determinations can be made offsets the need for prior calibration, especially when a particular polymer is going to be characterized routinely by this method. 

Molecular weight calibration from a monomer to several million daltons can be carried out by a variety of techniques. Because narrow standards of p(methyl methacrylate) (pMMA) are available, these are often used. Narrow standards of p(styrene) (pSty) are also available and can be used. Using the Mark-Houwink-Sakurada equation and the parameters for pSty and pMMA, a system calibrated with pSty can give pMMA-equivalent values, and vice versa. 

At the moment, one recommends to determine the molecular characteristics of pectins using SEC chromatography equipped with a differential refractometer, a multiangle laser light scattering detector and a viscometer as previously described [25]. This technique needs no calibration with the usual molecular weight standards such dextrans and pullulans... 

Molecular weight distributions were examined by high performance size-exclusion chromatography (HPSEC) as described [22] on two serial Shodex OHpak KB-803 and KB-805 columns (0.8 x 30 cm Showa Denko, Japan) with a OHpak KB-800P guard column (0.6 x 5 cm), equilibrated at 1 mL/min in 0.1 M UNO3. The system was calibrated with a pullulan calibration kit (Showa Denko). 

There are three imknowns, K, a and. One might question the availability of Mark-Houwink constants for the polymer in the open literature. Mark-Houwink constants in the literature differ widely for the same polymer and it is difficult to decide on the correct pair to employ. Another problem which can arise is that the universal molecular weight calibration curve may not apply exactly for the polymer in question. The use of the true Mark-Houwink constants would therefore introduce an error in the molecular weight calibration. Calibration with a broad MWD standard should eliminate this error. The Mark Houwink constants obtained in the calibration would in this instance be effective rather than true values. 

The column set was calibrated with Pressure Chemical polystyrene standards over the molecular weight range of interest. 

During production and characterization of various internal animal tissue reference materials for a number of metals, a comparative study was performed for Pb in six bovine teeth and two bovine bone materials using calibration with a solid RM and two versions of wet chemical analysis with GF-AAS and electrochemical (DPASV) detection. There was good agreement in the range of approx. 1.3-3 tng/kg dry weight for all techniques used (Liicker et al. 1992). 

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. 

Molecular weight measurements were determined by size exclusion chromatography on a high pressure liquid chromatograph equipped with a differential refracto-meter. A Waters Styragel HR 5 i column set (106 104 500 A) was employed and calibrated with PS standards. THF was used as solvent at a flow rate of 1 ml/min. 

Number-average molar masses were determined using a vapor pressure osmometer (VPO) (Hitachi 117 Molecular Weight Apparatus) at 54.8 0.1°C in toluene (Fisher Scientific, certified A.C.S.) which was distilled from freshly crushed CaH2. The VPO apparatus was calibrated with pentaerythritol tetrastearate (Pressure Chemical). Gel permeation chromatographic (GPC) analyses were performed in tetrahydrofuran by HPLC (Perkin-Elmer 601 HPLC) using six y-Styragel columns (106, 105, 10l, 103, 500, and 100 A) after calibration with standard polystyrene samples. 

One acceptable suggestion is to perform the regression with weighted response values ( ) where the weights are the inverse of the variance at each level of the calibration. However, since the true weights are not known, the determination of the weight values at each level of the calibration is not reliable. 

EquUibrium ultracenttifiigation has played a crucial role in establishing the molecular weights of protein molecules on an ab initio basis [3,4], that is, without requiring calibration with macromolecules of known molecular weight. 

Microspheres were monitored by scanning electron microscopy (SEM JEOL 35C), and their diameters were determined from the corresponding SEM microphotographs. Typically, ca. 500 particles in randomly sampled areas of microsphere specimens were analyzed. Molecular weight of poly(L-Lc) was determined by GPC. A system consisting of a LKB 2150 pump, Ultrastyragel 1,000, 500, 100, 100 columns, and Wyatt Optilab 903 interferometric refractometer was used for the measurements. GPC traces were analyzed by using calibration with narrow polydispersity < 1.15)... 

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