Triple detection

MWD. By tetra-detection GPC there is however a danger of information overload. It is usually more comprehensible if the Triple Detection calculations are repeated but with data from the spectrometer replacing that of the refractometer. Since all the detectors are on-line all the time it is easy for software to mix and match as required. 

Figure 3.18 contains data on myoglobin obtained using a triple detection setup. A molecular weight of 21,100 is found with a viscosity of 0.0247 dl/g, and from this a hydrodynamic radius of 2.06 nm, which is essentially the same as the Stokes value of 2.0 nm reported for myoglobin. 

A useful approach to detection in polymer HPLC presents the on-line hyphenation of different measurement principles. For example, an RI detector combined with a UV photometer produces valuable additional information on the composition of some copolymers. Further progress was brought with the triple detection RI plus LALS plus VISCO [313], which is especially suitable for branched macromolecules and the tetra detection UV plus RI plus LALS plus VISCO, which enables characterization of some complex polymer systems, exhibiting a distribution not only in their molar mass and architecture, but also in their chemical composition such as long chain branched copolymers. 

Schroers, H.-J. and Jermann, E., Determination of physiological levels of volatile organic compounds in blood using static headspace capillary gas chromatography with serial triple detection, Analyst, 123, 715-720, 1998. 

The product obtained was analyzed by gel permeation chromatography, GPC, using a Viscotek TDA 302 Triple Detection System with Light Scattering, Viscosity and RI Detection. The columns used were 2x ViscoGel GMPWxl (Mixed Bed), and the eluent was aqueous 0.8 M NaNC>3 at pH 7. The eluent flow rate was 0.6 ml/min. and the oligomer concentration approximately 1 mg/ml. The temperature was 35 °C. 

Another elegant method to characterize linear versus cyclic macromolecular chains is the SEC triple detection analysis. Absolute molar masses and intrinsic... 

Acknowledgements Francine Guida-Pietrasanta, Amedee Ratsimihety and Bernard Boutevin are acknowledged for suggestions and support, and Christine Joly-Duhamel for triple detection SEC analysis. CL s Ph. D. funding was supported by a grant from the French Ministry of Research and Education. 

Present emphasis is being placed on the use of detector combinations in fact, the triple-detection system , SEC-light-scattering-vis-cometry-differential refractometry, is being used more frequently, sometimes with the addition of an on-line UV detector to monitor composition (20). 

The RI constant, which relates the RI units to sample concentration, was determined by the dnjdc method of Wyatt Technology. The RI constant exhibited some variation at times, so that its value hacT to be adjusted in order to match the calculated mass with the injected mass. This variation was attributed to an intermittently faulty RI detector. The triple detection system had sufficient redundancy that accurate values of and [r ] could be obtained even when one component was not working well. 

It appears that for low values of Rg (10-20 nm), the values of Rg that were calculated from the Ptitsyn-Eisner equation were more reliable than those obtained from light scattering in an aqueous medium. Accordingly, for accurate work over a broad range of molecular weights and sizes, a triple detection system is advantageous and recommended. 

Multidetector GPC software , a PC-DOS package written by Lesec (6), was used for triple detection GPC. For data acquisition, the personal computer is connected to the 150 CV and the CMX 100 through a CEC IEEE board (Capital Equipment Corporation, Burlington, MA) and a 199 scanner multimeter (Keithley, Cleveland, OH). Molecular weights are calculated using both the LALLS detection and the viscometric detection with a combination of the classical molecular weight calibration curve and the viscosity law of the standards (6). 

The characterization of star-branched polymers has been performed using triple detection because it was not obvious, in the beginning of this study, that universal calibration could be applied to star-branched polymers. In fact, the GPC software used handles experimental data as a double dual detection, GPC-viscometry and GPC-LALLS. Experimentally, it has been found that excellent agreement between results from these two sets of data can be obtained. GPC-viscometry uses a universal calibration curve and GPC-LALLS is free of any molecular weight calibration curve. Therefore, the universal calibration works well with very long chain branched polymers, even with a very particular... 

Multiple detection applied to the SEC characterization of copolymers is attractive because it yields both CCD and MWD information. A dual detection system based on two concentration detectors, for example, RI and UV, is useful where narrow standards of the homopolymers are available and where both homopolymers obey universal calibration. However, in other copolymer systems the addition of a third detector, LALLS, can offer the advantage of on-line determination of molecular weight for each eluting species. The triple detection approach gave similar values to the dual detector approach for a model copolymer system (PS-PMMA) studied. It was also applicable to a more difficult copolymer system (PS-PEO), although it appeared that where one homopolymer was present in very small quantities, an average p value gave more consistent results than correction for pi across the distribution. 

SEC with On-Line Triple Detection Light Scattering, Viscometry, and R( Susan V. Greene... 

New electronics and improved computer data acquisition capabilities have permitted the development of SEC with on-line triple detection using LS, VISC, and re-fractometry. On-line triple detection is known as size-exclusion chromatography cubed (SEC ) with the three dimensions being defined by the three detectors [3]. The use of SEC eliminates the requirement for column calibration, unlike conventional and universal calibration, where a premium is put on control of variables such as flow rate, temperature, and column resolution. SEC can offer advantages in polymer production quality control as well as in research and development of new polymers. 

In special circumstances, detectors can be arranged in parallel by means of a splitter. The parallel triple detection of catecholamines is a good example of this, an electrochemical process being accompanied by two different methods of derivatization and subsequent fluorescence detection. 

FIGURE 9.11 Schematic diagram of an SEC instrumentation with triple detection system. (Courtesy of Polymer Laboratories.)... 

A more recent analysis of the molecular weight distribution by SEC using a triple detection (viscosity, concentration, molecular weight) has been described [51-53]. It was performed on heterogeneous chitosans, obtained from commercial sources after solid state treatment and... 

In order to validate the system, external sampling under pressure during the reaction was performed. The reactant contents were analyzed by dynamic head space gas chromatography and the polymer molecular weight distribution by size exclusion chromatography with triple detection. 

Size-exclusion chromatography coupled with triple detection... 

Figure 2.2 Typical setup of size-exclusion chromatography equipped with triple detection for determination of the moiecuiar weight of polymers without the need for prerequisite calibration. DRi, differential refractive index detector DV, differentiai viscometer I, injector MALS, multi-angle light-scattering detector (depending on the model, the scattered light is measured at 3 or 18 different angles) P, pump. The central unit includes a computer and software.

This also means that calibration is required in methods based on viscosity measurements before the method can be applied to characterise the molecular weight of a given polymer. Such calibration is tedious and requires that the molecular weights of a series of the polymer have been characterised by another technique in order to establish the relationship with the intrinsic viscosity. At present, this can be performed using the SEC method coupled with triple detection. It is noteworthy that calibration of the Mark-Houwink-Sakurada equation is valid only for one couple including a polymer and a solvent at a given temperature. 

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