2016 Volume 33 Issue 1 Pages 13-
Sequential injection analysis (SIA) protocols for the determination of phosphorus and mineral iron (Fe) in the Lagos Lagoon sediment were developed by optimizing some existing standard methods. Sandwiched sample was found to offer higher sensitivity than a 2-zone stack for P SIA. The injection volumes of sample and reagent for P analysis were 40 µL and 20 µL (split into two 10-µL zones) respectively while 150 µL of sample and 10 µL of reagent were injected in Fe analysis. The sampling rates were 31 h-1 and 75 h-1 for P and Fe SIA protocols respectively. Quantitative digestion of total P was achieved by a sediment-to-persulfate ratio of 1:3 by mass in 2.0 mL of 0.3 M NaOH. Average recovery of bioavailable P in matrix samples was 91.7 % and average recoveries of total P were 111.5 % and 96.6 % in matrix samples and blanks respectively. Average recovery of mineral iron in matrix samples was 94.3 % while average recovery in blanks was 97.4 %. The method detection limits were 1.4 mg P kg-1 and 2.6 mg P kg-1 for bioavailable-P and total-P methods respectively while the method detection limit for mineral iron method was 0.44 mg Fe kg-1. The combination of neutralization and dilution of bicarbonate extract prevented CO2 interference during SI absorbance scanning. The performance of these methods indicated their suitability for sediment P and Fe monitoring of the Lagos Lagoon system.
