The measurement of photochemically generated nitric oxide radicals (NO) in natural waters has long been an arduous task because of a lack of simple analytical techniques, even though the environmental significance of this radical is paramount. We have developed a simple analytical method for the determination of photochemically generated NO in natural waters using 4,5-diaminofluorescein (DAF-2) as a probe compound. This method is based on the reaction of photoformed NO with DAF-2 in air-saturated solution to produce a highly fluorescent triazolofluorescein (DAF-2T) product. DAF-2T was determined by using reversed-phase HPLC with fluorescence detection, with excitation and emission wavelengths of 495 and 515 nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of 0.025-10 nM DAF-2T. The coefficients of variance for the measurements of the signal intensities of DAF-2T (from the photolysis of 0.5 microM and 5 microM NO(2)(-) with DAF-2) were less than 5% and 3%, respectively. For a total irradiation time of 30 min, the detection limit of the photoformation rate of NO was 1.65 x 10(-13) M s(-1), defined as 3sigma of the lowest measured DAF-2T concentration (0.025 nM). The proposed method is relatively unaffected by potential interferents in seawater. The method was employed to determine the photoformation rate of NO in the Seto Inland Sea and the Kurose River in Hiroshima Prefecture, Japan. The measured NO photoformation rates in seawater and river water samples ranged from (5.3-32) x 10(-12) M s(-1) and (9.4-300) x 10(-12) M s(-1), respectively.

Nitric oxide (NO•) is an active odd-nitrogen species that plays a critical role in determining the levels of ozone (O₃) and other nitrogen species in the troposphere. Here, we provide experimental evidence for photochemical formation of NO• in seawater. Photoproduction rates and overall scavenging rate constants were measured by irradiation of surface seawater samples collected from the Seto Inland Sea, Japan. Photoproduction rates of NO• ranged from 8.7 × 10⁻¹² M s⁻¹ to 38.8 × 10⁻¹² M s⁻¹ and scavenging rate constants were 0.05-0.33 s⁻¹. The steady state concentrations of NO• in seawater, which were calculated from the photoproduction rates and scavenging rate constants were in the range 2.4-32 × 10⁻¹¹ M. Estimation from the scavenging rate constant showed that the NO• lifetime in seawater was a few seconds. Our results indicate that nitrite photolysis plays a crucial role in the formation of NO•, even though we cannot exclude minor contributions from other sources. Analysis of filtered and unfiltered seawater samples showed no significant difference in NO• photoformation rates, which suggests a negligible contribution of NO• produced by photobiological processes. Using an estimated value of the Henry's law constant (kH ≈ 0.0019 M atm⁻¹), a supersaturation of surface seawater of 2 to 3 orders of magnitude was estimated. On the basis of the average values of the surface seawater concentration and the atmospheric NO• concentration, a sea-to-air NO• flux was estimated.

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The inhibitory potentials of ethanolic extracts and four fractions of the stem bark of Ficus asperifoliaMiq. for the corrosion of mild steel were assessed using weight loss method, Fourier atomic absorption spectroscopy, scanning electron microscopy (SEM). The effects of varying immersion period, concentration of the inhibitors and temperatures for mild steel corrosion in 5 M HCl acid solution were carried out. A detailed kinetic reaction, thermodynamic (Ea, ∆H, ∆S) and adsorption isotherm studies were obtained. The crude extract of F. asperifolia (EFA) has the highest inhibition efficiency of 55%. The inhibitory efficiency of the four fractions of F. asperifolia (EFA) compared with the crude extract was in the order ethyl acetate > n-hexane > butanol > EFA > Aqueous. The inhibition efficiency was found to increase with increase in the extracts concentration but decreased with temperature. Corrosion rate increases with time but decreases with extracts concentration. The kinetic studies of the data followed a first order reaction. Thermodynamic studies revealed that corrosion inhibition may be due to spontaneous mixed adsorption of the plant constituents on the metal surface. Experimental data were fitted to Langmuir, Freundlich and Temkin adsorption isotherms. The plant investigated showed a good potential for green corrosion inhibitors. Investigation of phytochemical constituents showed that the extracts contain alkaloids, flavonoids, saponins, tannins anthraquinones and reducing sugars.

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