How to broadening the analysis Range of an Infinity II ELSD 1290 - G7102A

I'm working with an Infinity 2  ELSD 1290 - G7102A to analyse Phospholipids in a fat sample. The range of the detector is limited to 70 000 LSU what is round about 100 µg/analyte. Is this already the physical overload of the detector or is it limited by settings. Is there a aposibility to get a broader analysis range e.g. up to 500 000 LSU. Due to shift in the baseline of the chromatogram there is at these method a high LOQ of 10 µg. #elsd_range_validation

  • Hello ,

     

    The maximum output of the detector is 1.280 Volts - this is fixed and not adjustable. If your compounds cause the detector to saturate and you see the top of the peak become flat, then either the concentration is too high, the injection volume too large, or there is excess offset of the baseline signal. The baseline can shift upwards if the Zero is used repeatedly to correct for a high offset, and this will subtract from the useable output range. Causes of high offset include improper evaporation settings, and impurities in the mobile phase, or contamination of the optical bench.  You can check the condition of the optical bench for contamination as follows:  With no flow going to the detector, change the mode from Standby to RUN. Observe the initial offset of the output signal on the detector display. It should only be about 50 millivolts. If it is significantly higher, in the hundreds of mVs then there is contamination and service is needed. Press the Autozero button.  The baseline should come to rest at 10 mV. If the resting baseline is good and the bench is not contaminated then look at sample concentration and injection volume reduction.

     

    -Howard White

  • Thank you for your reply, the problem is that the graph signal unit doesn't appears in mV but in LSU and I dont know how  mV are converted in LSU.

  • For the purposes of this troubleshooting, the unit of measure doesn't matter and you can substitute mV for LSU one for one. But it's important to understand the photomultiplier output range of this detector is automatically scaled depending on the signal amplitude, and the ratio of mV to LSU changes making a direct conversion impossible. This is also the reason the analog output cannot be used. Hope this is clear.

     

    - Howard

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