Sandwich sequence (A) of molybdate, sample and ascorbic acid (100mcrL each), was assembled in a holding coil of microSI-LOV system (B), equipped with a reactor. The holding coil and reactor had same dimensions (2m of 0.8mm I.D. tubing) and were heated to 50 C.
The assembled sequence was split by flow reversal, and the split section was pushed into the reactor. Next, the section left in the holding coil was transported trough the flow cell (12 cm long light path) and first peak was recorded (C). Finally the zone from reactor was aspirated into holding coil, the flow was reversed and the zone passed trough the flow cell, while second peak was recorded. Split ratio was investigated as shown in (C) and 200/100 ratio (bluer track) was selected for acquiring calibration curves, obtained with the first peak (D window 20-30sec) and the second peak (E 40-50 sec).The first peak yields higher sensitivity and better LOD, but above 400 ppB P the calibration fails, due to lack of reagent. The calibration obtained with second peak extends the calibration range, thus allowing assay of samples that otherwise would have to be diluted, and assayed again.
Sample Split: Wide Range Phosphate Assay
5 to 1200 ppB N
2.2.30.
