pFI Method for Ammonia
(Salicylate - Betrholet Blue Method)
The formation of indophenol blue at room temperature is too slow, and therefore the influence of temperature at a dwell time of 80 seconds was investigated first, using 1ppM N standard solution. As seen from (A). the response decreased above 40 C due to decomposition of indophenol blue.
By increasing dwell time from 10 to 100 sec at 40 C, the sensitivity of the assay increased 100 times (B). In the mid ppB range the calibration graph was linear (C). Ultimately, with 180 sec dwell period (D) 10 ppB N (as NH4) was reached (All runs in duplicate are shown overlaid).
1.2.32.
