Broad standard calibration

Robustness of methods based on broad-on-nar row approach (one of narrow standar ds is used as broad standard for correction of calibration function) is higher but some disadvantages also are observed. 

Long-time reproducibility of elution profiles broad standard calibration with dextran T-500 transformation of a scb-type calibration function into nb/Icb-type via universal calibration dp of synthetic glucans in the presence of significant amounts of monomer mass and molar degree of polymerization of Triticale (hybride) starch... 

Absolute system calibration with a set of narrow distributed nb glucans (pullulans) by means of dual detection of mass and scattering intensity applying a mixed peak position/ broad standard calibration... 

B. Broad Standard Size Exclusion Chromatography (SEC) Calibration... 

Establishing a calibration function with one single broad distributed sample is an alternative to traditional peak postion calibration of SEC systems with a set of narrow distributed standards. An obvious advantage of this technique is time for peak position calibration elution profiles for the set of standards need to be determined for broad standard calibration the elution profile of one sample needs to be determined only. Establishing a linear calibration function with a broad distributed standard includes startup information [M (true), Mn(true)] and an iterative (repeat.. . until) algorithm ... 

FIGURE 16.5 Broad standard calibration (linear mode) of a semipreparative Sephacryl S-IOOO system (95 x 1.6 cm) with an aqueous mixture of Blue Dextran, Dextran T-SOO, and glucose eluent 0.005 M NaOH V, i = 75 ml. = 162 ml. 

To improve interpretation of nb/lcb glucan profiles from the S-500/S-1000 system, the initially obtained broad standard calibration function was... 

FIGURE 16.10 Intial dextran calibration ( ) and resultingnb/Icbglucan calibration ( )forthe Sepha-cryl S-SOO/S-1000 (60 + 9S X 1.6 cm) system achieved from broad standard calibration with Dextran T-SOO and universal calibration, respectively Staudinger/Mark/Houwink constants (dextran Ksu = 0.0978 ml Mg . Osw = O.SO nb/lcb amylose = pullulan K pi. = 0.0268 ml M g . = 0.6S). 

Alternatively, either the Elamielec or the integral broad standard calibration procedure can be used. For this approach, the broad standard would be initially analyzed using a calibration based on some convenient standard that may be quite dissimilar in chemistry from the standard. From that point forward, the system is calibrated with the secondary standard. Thus, changes that affect the sample will be compensated for in the calibration procedure. 

An added benefit of the direct SEC-[n] calibration approach is that a new independent way of determining K and a values, using only broad MW standards, has also resulted. As few as three standards (or four, if all are narrow MWD) are needed to obtain both MW and [x]] calibration curves for a particular polymer-solvent system by using the broad-standard, linear calibration approach. From the experimental calibration constants of the two calibration curves, one can calculate K and a directly as described later. 

Figure 4, Comparison of broad standard with peak position SEC-[rj] calibration curves ([rj = loge [7/] = loge El — EgV (-0-) peak position calibration...

C. Linear SEC-[nl Calibration Using Broad Standards. It is to be noted that the viscosity calibration curve in Figure 3 is essentially linear. This linearity is derived from bimodal SEC column sets. 

The broad-standard linear calibration curves for polystyrene in THF in Figure 1 and 4 are used to illustrate the K and a calculations as follows. The particular calibration curves are found to correspond to the following calibration equations ... 

The validity of a practical method of direct viscosity calculation from size exclusion chromatographic analysis is demonstrated. The method is convenient to use and is not limited by the availability of narrow MWD standards. It is possible to accurately measure polymer Mark-Houwink constants using the suggested broad standard SEC-[n] and SEC-MW calibration procedure. 

One possibility is that although averages for polystyrene standards require correction, those for PMMA would not According to symmetrical axial dispersion theory (5) the correction depends upon both the slope of the calibration curve (different for each polymer type) and the variance of the chromatogram of a truly monodisperse sample. Furthermore, the calibration curve to be utilized can be obtained from a broad standard as well as from monodisperse samples. The broad standard method may itself incorporate some axial dispersion correction depending upon how the standard was characterized. 

Figure 3. Molecular weight calibration curves for polyvinyl chloride obtained using universal calibration and one and two broad MWD standards (two broad standard method (0) [rj = 7.06 X 10 single broad standard method ...

Extrapolations can also be applied to log Tg-retention volume plots (dashed line in Figure 5) to provide a better estimate of the number-average radius. There is reasonable superposition of the values of the broad standard on the narrow standard calibration data, but unlike the log M plot in Figure 4, there is considerable scatter in the data at long retention volumes (small sizes). In this region the 15° and 90° signals are nearly identical and the ratio of the two signals depends heavily on... 

Detectors vary in their response to the compounds being sensed, with respect both to the amount and to the class of compound. Since the thermal conductivity of a mixture of two gases (the carrier gas and the sample) is not necessarily a linear function of composition, absolute quantitative measurements with thermal-conductivity detectors can only be obtained after calibration with standard compounds. However, response to structurally similar compounds is quite uniform, and reliable, relative, quantitative data can be obtained with this detector. Ionization detectors give a signal that is related directly to the mass or the concentration of the components, and the response is uniform over a broad range of operating conditions these detectors are, therefore, ideally suited for quantitative work. 

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