The compouad 2,4-D (2,4-dichlorophenoxyacetic acid) is the most widely used herbicide in the United States, and its widespread use may result in the applied compounds being carried or washed into nearby water courses, rivers, lakes, or groundwater reservoirs. This situation has stimulated basic studies on the chemical and physical behavior of 2,4-D in water. Studies by various authors show that 2,4-D degrades within several weeks in soils; it can persist for up to six months or more in natural waters. The ionization constant of 2,4-D has been redetermined at 25øC from conductivity measurements. A value for the ionization constant of 1.169 X 10 -a was calculated when the equivalent conductance at infinite dilution of 2,4-D was computed from the equivalent conductance at infinite dilution of the sodium salt of 2,4-D, using the Kohlraush method of independent ion mobiltries. These results differ from those obtained by other workers, who have computed the equivalent conductance at infinite dilution of 2,4-D, using the equations derived by Fuoss and his co-workers for the conductance of strong electrolytes in polar solvents. (Key words: Geo-
The influence of experimental parameters on detection sensitivity was determined for laser Raman analysis of dissolved solutes in water. Individual solutions of nitrate, sulfate, carbonate, bicarbonate, monohydrogen phosphate, dihydrogen phosphate, acetate ion, and acetic acid were measured. An equation is derived which expresses the signal-to-noise ratio in terms of solute concentration, measurement time, spectral slit width, laser power fluctuations, and solvent background intensity. Laser beam Intensity fluctuations at the sample and solvent background intensity are the most important limiting factors.
Abstract— Suspensions of goethite (α‐FeOOH) were photolyzed in aerated ethylene glycol‐water solutions at pH 6.5, with ultraviolet light in the wavelength range300–400 nm. Under these conditions, formaldehyde and glycolaldehyde were detected as photoproducts. Quantum yields of formaldehyde production ranged from 1.9 7times; 10‐5 to 2.9 × 10‐4 over the ethylene glycol concentration range of 0.002‐2.0 mol/ℓ, and gave evidence that the reaction occurred at the goethite surface. Quantum yields of glycolaldehyde were 20% less than those of formaldehyde, and displayed a concentration‐dependent relationship with ethylene glycol similar to that of formaldehyde. Immediately after photolysis, Fe2+ was measured to be 4.6 × 10‐7 mol/ℓ in an aerated suspension containing 1.3 mol/ℓ ethylene glycol, and 8.5 × 10‐6 mol/ℓ in the corresponding deoxygenated suspension. Glycolaldehyde was not generated in the deoxygenated suspensions. These results are consistent with a mechanism involving the transfer of an electron from an adsorbed ethylene glycol molecule to an excited state of Fe3+ (Iron[III]) in the goethite lattice, to produce Fe2+ and an organic cation. In a series of reactions involving O2, FeOOH, and Fe2+, the organic cation decomposes to form formaldehyde and the intermediate radicals “OH and” CH2OH. OH reacts further with ethylene glycol in the presence of O2 to yield glycolaldehyde. Aqueous photolysis of ethylene glycol sorbed onto goethite is typical of reactions that can occur in the aquatic environment.
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