Detector for SEC

The sample fluid could be any neat liquid or a sample of polymer solution. Under favorable conditions, a single viscosity determination on a polymer solution at high dilution can provide a direct measure of the polymer intrinsic viscosity, without the need of polymer concentration extrapolation. With this viscometer used as a continuous viscosity detector for SEC, it is possible to achieve SEC molecluar weight calibration by way of the universal SEC calibration methodology without the need of molecular weight standards for the unknown polymers. 

On-line MS detectors for SEC offer great promise for serving simultaneously as an absolute detector, concentration-sensitive detector (i.e., total ion current), and composition detector, especially for oligomers and low-MW polymers. Successful developments in the use of matrix-assisted laser desorption ionization (MALDI) MS for high-MW polymers are extremely encouraging, and on-line MALDI MS should... 

Copolymer Analysis. Even though the overall copolymer composition can be determined by residual monomer analysis, it still is necessary to have reliable quantitative techniques for copolymer composition measurements on the actual copolymer, mainly because concentration detectors for SEC or HPLC are sensitive to composition and because the conversion histories are not always available. Some of the techniques used to determine copolymer composition are melt viscometry (46), chemical analysis, elemental analysis, infrared spectroscopy (IR), Nuclear Magnetic Resonance (NMR), ultra-violet spectroscopy (UV), etc. Melt viscometry, chemical and elemental analysis are general techniques that can be applied to almost any polymer. The spectroscopic techniques can be applied depending on the ability of the functional groups present to absorb at specific wavelengths. 

Attempts to measure MM by MALDl of polydisperse polymer samples yielded poor results. Instead, correct MM estimates could be obtained when MALDI-TOF was used as a detector for SEC, collecting the SEC fractions and analyzing them with MALDL... 

General issues of mobile phases and detectors for polymer HPLC were in detail discussed in sections 11.6.2 and 11.6.1.4, respectively. In this section, only peculiarities of mobile phases and detectors for SEC are highlighted. 

In their choice of instruments, the operators are almost entirely dependent on the producers of detectors. There is no univeral apparatus for polymer HPLC and no universal detector for SEC. It is important to plan future use of the instrument before its purchase. 

For protein characterization, SEC-LS has been used as an analytical procedure for determining the molecular weights of unknown samples and also for studying protein association. In using an on-line light-scattering detector for SEC... 

Appendix Instrument Companies Light-Scattering Detectors for SEC... 

In 1953, Stockmayer and Fixman observed that the ratio, h, of hydrodynamic or Stokes radii (/ h) of the branched and linear macromolecules could also be used as a measure of branching. The relatively recent introduction of online quasielastic light scattering (QELS, also known as dynamic light scattering and as photon correlation spectroscopy) detectors for SEC permits direct determination of h by... 

PE Performed a systematic evaluation of the performance of LALLS and MALLS detectors for SEC. It was noted that MALLS detection offers the advantage of determining the radius of gyration at each retention volume. 38... 

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