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PDI Values Worse than Expected

MargotH

We currently measure PDI values of 1.4 for the EasiVial standards which should be around 1.1 normally. The columns we use are MixedC and Oligopore in series and are in only in use for 7 months now. The first months all peaks were within their normal PDI range but this has slowly increased. Is it normal that the columns deteriorate this fast or are there other things to consider? No structural changes have been made to the system during  this period.

Thanks!

Margot

  • +1

    Hi Margot,

    It may well be that the column performance has deteriorated so much within the 7 months that the EasiVial standards are measured with poorer PDI values. The column performance can be tested with regular plate count determinations. It is a measure of the quality of the entire system and is closely related to the columns. Butylhydroxytoluene or toluene can serve as a standard for THF applications e.g. (2 mg/mL in the running medium). Has the elution volume also shifted from the peak maxima? Have you added a flow marker to the vials or measured a blank regularly - has the elution volume shifted here?
    Of course, the standards themselves could also be the problem; however, in the case of polystyrenes for calibration this is rather unusual. 
    In addition to standards and columns, clogged filters (if used) before the detectors could also be problematic. However, this would also be reflected in increased system pressure, for example. 

    B rgds,

    Anne

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