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Efficiency of Hexane Extraction of Napropamide from Aldrich Humic Acid and Soil Solutions

Dep. of Environmental Science, Univ. of California, Riverside, CA 92521-0424;

M. Ben-Hur

Agric. Res. Organ., Volcani Center, P.O.B. 6, Bet Dagan, Israel.

^* Corresponding author (williamc{at}mail.ucr.edu).

ABSTRACT

Dissolved organic matter (DOM) has been shown to form a stable complex with Napropamide [2(-naphthoxy)-N,N-diethyl propionamide] and to facilitate its transport through soil columns. Liquid-liquid extraction of organics is a common method to transfer napropamide from water into an organic phase for gas chromatography analysis. A study was conducted to determine the effect of Aldrich humic acid, soil-derived dissolved organic matter, electrical conductivity, and hydrogen ion activity on the ability of hexane to extract napropamide from solutions and from soil extracts. The electrical conductivity of Aldrich humic acid solutions (0.0, 48, and 100 mg C L^–1) were adjusted to 0.01, 0.97, and 1.69 dS m^–1 by adding NaCl and CaCl₂, and pH (8.2, 7.4, and 5.6) was adjusted using HCl and NaOH. Electrical conductivity had no effect on extraction efficiency. In the absence of DOM pH had no effect on extraction efficiency. Extraction efficiency decreased with increasing DOM concentration. Maximum reduction in extraction efficiency occurred in the presence of DOM when solution pH was near neutrality. A maximum extraction efficiency of 100% was observed in the absence of DOM and a minimum of 68% when napropamide was added to DOM solutions at pH 8.2 and then lowered to pH 5.6. Management practices such as liming and allowing napropamide to dry on the soil may increase environmental transport. Also quantification of napropamide in environmental samples can be affected by DOM.

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