A multi-pumping flow system with on-line photochemical conversion and improved sensitivity for phosphorus fractionation in freshwaters

• Published in: International journal of environmental analytical chemistry Vol. 93; no. 13; pp. 1389 - 1401
• Main Authors: Rocha, Diogo L., Rocha, Fábio R.P.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 01.11.2013; Taylor & Francis LLC
• Subjects: Analytical chemistry; flow analysis; Fractionation; Freshwater ecology; Molybdenum; Phosphorus; photo-oxidation; Photochemistry; waters, phosphorus
• ISSN: 0306-7319; 1029-0397
• DOI: 10.1080/03067319.2012.746324

A flow-based procedure with solenoid micro-pumps was developed for phosphorus fractionation (dissolved organic and inorganic phosphorus) in freshwaters. The spectrophotometric detection was based on the formation of molybdenum blue and the organic species were on-line photo-converted to orthophosphate. The analytical response was linear within 10 and 75 µg L −1 with a detection limit of 2.0 µg L −1 (99.7% confidence level). Coefficient of variation of 1.8% (50 µg L −1 P, n = 20) and sampling rate of 40 determinations per hour were achieved. Per determination, 160 µg (NH 4 ) 6 Mo 7 O 24 , 10 µg SnCl 2 , 640 µg K 2 S 2 O 8 and 10 mg NaOH were consumed, generating 2.0 mL of waste. Slopes of analytical curves obtained for four different organic phosphorus species agreed with those obtained for orthophosphate, indicating quantitative conversion. The results for freshwater samples agreed with those obtained by the AOAC reference procedure at 95% confidence level. The organic matter did not interfere in the photo-oxidative process. The proposed procedure is a fast and environmentally friendly alternative for the phosphorus fractionation in freshwaters.