The combination of heated holding coil (A) with the flow cell kept at room temperature is the best choice for SHC protocol, since the reaction reaches equilibrium within seconds in a holding coil thermostated at 55 C. Therefore nothing would be gained by heating the flow cell as well. Also because there is only a small difference between yield of reactions carried out at 3 and 5 seconds stop flow period, the assay protocol for the range of 0 750 ppB N was designed with 3 seconds wait period (B).
This approach, similar to that used for phosphate assay yielded a high sample throughput of 108/s hr, with no carryover and stable baseline (C). The readout shows a spike, preceding the ammonia response peak, but since this spike is reproducible (green line), and is well temporary resolved, it does not influence the calibration curve (D). The spike is caused by reagent color (nitropruside), at the interface of water (carrier) and of the reagent.
Fast Ammonia Assay
0 to 750 ppB LOD 1.8 μM N
2.2.35.
