Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/4/2005
Publication Date: 6/27/2005
Citation: Zhu, H., Derksen, R.C., Krause, C.R., Fox, R.D., Brazee, R.D., Ozkan, H.E. 2005. Effect of Solution pH Conditions on Fluorescence of Spray Deposition Tracers. Applied Engineering in Agriculture. 21(3):325-329.
Interpretive Summary: Agricultural production and storage consumes about 75% of total pesticide in the USA. However, pesticide use can potentially raise concerns about health risks from residues in food and drinking water, worker hazards, and negative impacts on wildlife and sensitive ecosystems. In pesticide spray application trials, it is important to know the spray quality and quantity reaching target areas. Fluorescent tracers provide a means of tracking spray movement when either environmental conditions or analytical techniques prohibit the use of active ingredients. Little information is available on their measurement accuracy due to questions of stability of fluorescence under different experimental conditions. In this research, the stability of fluorescent intensity of five fluorescent tracers commonly used in evaluation of pesticide spray application efficiency was determined with various solution pH conditions. Test results indicated fluorescent intensity of water soluble tracers was significantly influenced by the solution pH conditions, but the effect was not the same for all tracers evaluated. It was concluded that the fluorescence of tracers should be examined under various pH conditions during the selection of tracers, and the wash solution pH should be adjusted to the alkaline state to minimize analytical errors. By following recommendations from this research to evaluate spray performances, high quality pesticide sprays can be achieved by researchers and pesticide spray applicators to improve pesticide spray application efficiency and reduce environmental contamination.
Technical Abstract: Stable analysis of fluorescence is essential to ensure accurate evaluation of pesticide spray application efficiency. The fluorescent intensity of five fluorescent tracers commonly used for the quantitative assessment of spray deposition and off-target loss was investigated with wash solutions over pH conditions from 6.86 to 10.4. The tracers selected in the tests were Fluorescein, Pyranine, Tinopal, Acid Yellow 7 and Eosin. The fluorescence of Pyranine was the most sensitive to the solution pH conditions, followed by Fluorescein and Tinopal, while Acid Yellow 7 and Eosin had a nearly constant fluorescent intensity over the pH range from 6.86 to 10.40. The fluorescence of Fluorescein increased 1.3 times, Tinopal 1.25 times, and Pyranine 3.0 times as the pH value increased from 6.86 to 8.43, but it became nearly constant when pH value was greater than 8.43. However, Pyranine, Fluorescein and Tinopal showed much stronger fluorescence than Acid Yellow 7 and Eosin with the same concentrations. A solution containing Fluorescein at pH 8.43 and higher demonstrated 124 times greater fluorescent intensity than the solution containing the same amount of Acid Yellow 7. The stability of fluorescent intensity should be examined not only with purified distilled water but also under various wash solution pH conditions during the selection of tracers for pesticide spray deposition and drift trials.