Green Chemistry–Sensitive Analytical Procedure for Photometric Determination of Orthophosphate in River and Tap Water by Use of a Simple LED-Based Photometer

ABSTRACT

In the current work a Green Analytical Chemistry (GAC) procedure for photometric determination of orthophosphate in river water at µg L⁻¹ concentration level is described. The flow system module and the LED-based photometer were assembled together to constitute a compact unit in order to allow that a flow cell with optical path-length of 100 mm was coupled to them. The photometric procedure based on the molybdenum blue method was implemented employing the multicommuted flow injection analysis approach, which provided facilities to allow reduction of reagent consumption and as well as waste generation. Aiming to prove the usefulness of the system, orthophosphate in river and tap waters was determined. Accuracy was ascertained by spiking samples with orthophosphate solution yielding recoveries ranging from 96% up to 107%. Other profitable features such as a wide linear response range between 10 to 800 µg L⁻¹ ; a detection limit (3σ criterion) of 2.4 µg L⁻¹ ; a relative standard deviation (n = 7) of 2% using a typical water sample with concentration of 120 µg L⁻¹ ; reagent consumption of 3.0 mg ammonium molybdate, 0.3 mg hydrazine sulfate, and 0.03 mg stannous chloride per determination; a waste generation of 2.4 mL per determination; and a sampling throughput of 20 determination per hours were also achieved.

KEYWORDS:

• LED-based photometer
• long pathlength flow cell
• multicommuted flow injection analysis
• orthophosphate and water
• spectrophotometry

ACKNOWLEDGMENTs

The authors acknowledge the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico do Brasil) for the financial support and CAPES (Coordenadenação de Aperfeiçoamento de Pessoal de Nível Superior) for a grant to Milton B. Silva.

Notes

∗Present address: Universidade Federal do Recôncavo da Bahia, Centro de Ciências Exatas e Tecnológicas, Cruz das Almas, 44.380-000, Bahia, Brazil.

Results are average of three replicates. ∗, ∗∗, and ∗∗∗ = water samples of Piracicaba River, Curumbataí River, and tap water, respectively. The trace notation indicates that the orthophosphate was not detected.

The notations ∗ and ∗∗ correspond to consumption and waste generated per determination, respectively.

An invited paper submitted to a special issue on Green Spectroscopy and Analytical Techniques, organized by Professor Miguel de la Guardia, of the Department of Chemistry, University of Valencia, Spain, and Professor Arabinda Kumar Das, of the Department of Chemistry, University of Burdwan, West Bengal, India.

Additional information

Notes on contributors

Sivanildo S. Borges∗

∗Present address: Universidade Federal do Recôncavo da Bahia, Centro de Ciências Exatas e Tecnológicas, Cruz das Almas, 44.380-000, Bahia, Brazil.