Solubility of Triazine Pesticides in Pure and Modified Subcritical Water

Abstract

Solubility measurements in pure and modified water serve as a basis for optimizing the subcritical water extraction of target analytes such as food contaminants. The solvent strength of the water is affected by both the system's temperature and the amount and type of cosolvent modifier that is added to the water, which causes a reduction in the dielectric constant of water. In the present work, the solubilities of the triazine pesticides atrazine, cyanazine, and simazine were measured in pure and modified water at temperatures ranging from 50 to 125 degrees C and at a pressure of 50 atm. The solubility data were obtained using a static solubility apparatus with on-line liquid chromatographic (LC) detection. By increasing the temperature of the water, the solubilities of the triazine pesticides increased approximately 3-fold in pure water for each 25 degrees C temperature increment. Cyanazine was 5 times more soluble than atrazine and an order of magnitude more soluble than simazine at 100 degrees C. The solubility of atrazine was also measured in ambient and hot water modified with ethanol and urea. At 100 degrees C, the solubility of atrazine is doubled when the water is modified with urea, and is increased over an order of magnitude when ethanol is used as modifier. The data, therefore, indicate that adding a cosolvent to water in addition to increasing the system temperature increases the solubilities of triazine pesticides in subcritical water. It was further determined that the solutes do not thermally degrade or hydrolyze at the temperatures reported in this study.

Extraction of Functional Substances from Agricultural Products or By-products by Subcritical Water Treatment

“…Ong and Len (2003) investigated the effect of the addition of ethanol (0 to 30%) into subcritical water on the extraction of berberine from a medicinal plant and found that the berberine content in the extracts increased with increasing amount of ethanol at treatment temperatures of 95 and 140℃ for 40 min. Modification of subcritical water with ethanol from 0 to 20% or urea at 28% (w/w) at 100℃ and 5 MPa increased the solubility of atrazine, a type of pesticide found in food commodities, from 500 to 6,000 mg/L (Curren and King, 2001). Choi et al (2003) applied subcritical water containing Triton X-100 at various concentrations above its critical micelle concentration to extract the pharmacologically active ingredients (ginsenosides) from the root of ginseng.…”

Properties of Rice Stem Extracts Obtained by Using Subcritical Fluids

“…The dielectric constant of subcritical water decreases to match that of a polar organic solvent by increasing the temperature, 7) and a further decrease is achieved by adding an organic solvent, i.e., ethanol or acetone. 8) It has been reported that the lignocellulosic materials submitted to a subcritical organic solvent produced a black liquor which had radical scavenging ability. [9][10][11] Chiou et al have reported that subcritical aqueous ethanol and acetone were effective for extracting carbohydrates and phenolic compounds from rice bran.…”

Correlation for the variations with temperature of solute solubilities in high temperature water

“…Solute solubility database and data correction Table 1 summarizes the solutes and solubility data sources [4][5][6][7][8][9][10][11][12][13][14] that were considered to derive an alternative correlation to Eq. (1) for the effect of system temperature on solute solubility [5] in liquid water, at the tabulated temperature and pressure ranges, and the units used to report the solute's solubility in water.…”

“…The starting point of our data correlation was a van't Hoff-type semi-logaritmic relationship for the solubility (x 2 ) versus the reciprocal of absolute temperature (T −1 ), as observed by Curren and King [7] for the solubility of triazine pesticides (atrazine, cyanazine, simazine) in HTW:…”