Feedback standard addition method coupled flow injection analysis : Validation by spectrophotometric determination of nitrite in seawater

The standard addition method is a powerful tool to eliminate matrix interferences and enables accurate determinations, but it is time-consuming and labor-intensive. This paper proposes a feedback standard addition method coupled flow injection analysis, FB-SAM/FIA, for the rapid and accurate determination of trace interest in seawater samples. This approach automatically prepares spiked samples by feeding back the peak height in the fiagram, thus significantly improving the sample throughput compared to the manual standard addition method. Spectrophotometric determination of NO2- with the Griess assay was used as an evaluation model. The proposed technique demonstrated a sample throughput of 3 samples/h, ranging from 0.0050 mg L-1 (LOD) to 0.125 mg L-1 NO2-. The accuracies of NO2- determination with FB-SAM/FIA and an absolute calibration method were tested using natural seawater and pseudo-seawater samples containing 0.040 mg L-1 NO2- in 0, 1, 2, 3, and 4% sodium chloride media. With the absolute calibration method, the calculated concentration increased with an increase in salinity, reaching an overestimation of about 40%. On the other hand, FB-SAM/FIA suppressed the errors in the range of -7.8% to 1.3% and applied successfully to the determination of NO2- in the natural seawater samples