Frequently Asked Questions

Amino Acid Analysis

Question

Why does sensitivity of ninhydrin response decrease with time?

Answer

The ninhydrin reagent, once prepared and when kept in optimum conditions can be stable for up to 4 weeks on the instrument. After this time, a decrease in sensitivity will be more pronounced, due to the unstable nature of the ninhydrin reagent.

Potential causes of fast decreasing ninhydrin sensitivity are:

  1. Low grade nitrogen or inert gas supply (must be 99.999%) used in preparation or on instrument.
  2. Incomplete dissolution of reagent before use.
  3. Nitrogen supply interrupted:
    • Cylinder valve stuck
    • PTFE purge tube trapped or disconnected
    • Reservoir bottle seal leakage
    • Reservoir still contaminated with detergent after washing (also gives yellow or pink colours with Virkon, decon).  Use only water for rinsing reservoir.
  4. If using a nitrogen generator, a leak in the nitrogen line will cause the generator to work above its normal capacity and will produce a lower grade nitrogen, leading to contamination of the ninhydrin with oxygen.
  5. Using non plastic coated bottles will cause UV light to go through and will accelerate the degradation process. Biochrom always supplies plastic coated Ninhydrin bottles.

BE AWARE THAT 99% OF NINHYDRIN SENSITIVITY ISSUES ARE RELATED TO THE NITROGEN SUPPLY USED DURING PREPARATION AND/OR STORAGE ON THE INSTRUMENT.


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