Inter detector delay triple detection

We use triple detection (LS, visco, RI) and analyse very broad samples. Despite the correction of the detector offset (inter detector delay) between the three detectors, the peak maxima are not congruent for my samples. What is the reason for this and what can I do?

  • The phenomenon you describe is inevitable for broad polymer samples: The signal intensity (SI), of all detectors depends on injected mass (concentration and injection volume), a sample related constant kSample (i.e., response factor), and a detector constant KDetector. Additionally, some detectors generate signals that are dependent on the molar mass of a sample.

    All detector signals follow the same equation: SI = KDetector · kSample · c · Mx
    SI = signal intensity
    KDetector = detector constant
    kSample = sample constant or response factor
    c = concentration
    M = molar mass

    The exponent x divides detectors into two categories:
    1) Concentration detector, x = 0
    2) Molar mass sensitive detectors, x ≠ 0 (LS detector x = 1; Visco detector x = α)

    Since constants and the influence of molar mass differ for concentration and molar mass-sensitive detectors, each detector yields a different signal output for a given sample. This difference is more pronounced for broad distribution samples. Please read more about GPC/SEC detection in the source (linked eBook) to my answer. Check further eBook material in the Wiki.

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