University of Lagos
Akoka, Lagos | Nigeria
Main Specialties: Chemistry
Additional Specialties: Analytical Chemistry (specifically flow injection techniques), Environmental Chemistry (specifically N and P emissions and discharges to air and waters respectively) and Green Chemistry.
Primary Affiliation: University of Lagos - Akoka, Lagos , Nigeria
J Anal Sci Technol (2017) 8: 5.
Journal of Analytical Science and Technology
Background: The substitution of hazardous analytical reagents such as Cd with benign alternatives for chemical determination is one of the principles of green chemistry. An eco-friendly Zn reduction method for nitrate determination was developed to achieve this end.
Methods: Online zinc reduction-sequential injection analysis (ZnR-SIA) protocol was developed for the determination of nitrogen (N) species in the Lagos Lagoon sediments by modification of some standard methods.
Results: The novel application of boric acid-borate buffer employed in borate-buffered granular Zn reduction suppressed gas evolution from the Zn micro-column, making the Zn reduction adaptable to online use, unlike the frequently used ammonia-ammonium buffer. Further results showed that the sampling rate for the two-zone stack was 65 h−1. The boric acid-borate buffer offered 5.9-fold and 1.3-fold of the instrument response given by the ammonia-ammonium buffer at 0.50 and 5.0 mg N L−1 respectively. The method detection limits of the ZnR-SIA for the three matrices studied were 24.6 μg N L−1 for reagent water, 0.383 mg N kg−1 for KCl-extractable nitrate, and 3.18 mg N kg−1 for total nitrogen. The average recovery of nitrate-N in matrix samples was 94.7%, and its precision was 4.52%. The average recoveries of total N in blanks and matrix samples were 97.9 and 93.2% respectively.
Conclusions: The method accuracies demonstrated the suitability of the ZnR-SIA for sediment N determination. Zn reduction is recommended where sustainable development is desired and is a potential substitute for the standard Cd reduction owing to Cd toxicity.
Keywords: Green chemistry, Sediment nitrogen, Online zinc reduction, Borate buffer, Sequential injection
J. Flow Injection Anal., Vol. 33, No. 1 (2016) 13-21
Journal of Flow Injection Analysis
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 and 75 h 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 and 2.6 mg P kg for bioavailable-P and total-P methods respectively while the method detection limit for mineral iron method was 0.44 mg Fe kg. The combination of neutralization and dilution of bicarbonate extract prevented CO interference during SI absorbance scanning. The performance of these methods indicated their suitability for sediment P and Fe monitoring of the Lagos Lagoon system.