Why might the primary amine be undetectable after a 10 min reaction but detectable after 15 min using the Primary Amino Nitrogen Assay Kit (K-PANOPA)? The test samples contain ammonium ions and primary amine.

Interference can be caused by ammonium ions during the first 10 minutes of the reaction generating a false positive reading so the reaction must be allowed to proceed for the recommended 15 minutes. This must also be done for the calibration reactions. Acidic or alkali samples should be neutralised (adjusted to pH 7) to avoid interference by ammonium ions. Interference can be assessed by quantitatively adding the isoleucince standard to a test sample and measuring the quantitative recovery of the standard. (See page 2 of the K-PANOPA booklet).

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