Natural waters color

Silica. The siUca content of natural waters is usually 10 to (5 x lO " ) M. Its presence is considered undesirable for some industrial purposes because of the formation of siUca and siUcate scales. The heteropoly-blue method is used for the measurement of siUca. The sample reacts with ammonium molybdate at pH 1.2, and oxaUc acid is added to reduce any molybdophosphoric acid produced. The yellow molybdosiUcic acid is then reduced with l-amino-2-naphthol-4-sulfoiiic acid and sodium sulfite to heteropoly blue. Color, turbidity, sulfide, and large amounts of iron are possible interferences. A digestion step involving NaHCO can be used to convert any molybdate-unreactive siUca to the reactive form. SiUca can also be deterrnined by atomic... 

Mapari, S.A.A. et ah. Exploring fungal biodiversity for the production of water-soluble pigments as potential natural food colorants, Curr. Opin. Biotechnol, 16, 231, 2005. 

Mapari, S. A.S. et al., Exploring fungal biodiversity for the production of water-soluble pigments as potential natural food colorants, Curr. Opin. BiotechnoL, 16, 231, 2005. Dufosse, L., Mabon, R, and Binet, A., Assessment of the coloring strength of Brevi-bacterium linens strains spectrocolorimetry versus total carotenoid extraction/quan-tification, J. Dairy ScL, 84, 354, 2001. 

All aqueous extracts are brown colored, and so is the Hillsborough River where samples of hydrilla are found. Examination of Table II, however, suggests that the location of the second peak in this water sample is significantly different from the other five samples. Presently, chromatograms of natural waters and the distribution of hydrilla are being obtained and compared with a view to being able to understand those factors that may limit the growth and spread of this noxious aquatic plant. 

Here is an extremely sensitive method for measuring nitrite (NOj) down to 1 nM in natural waters. The water sample is treated with sulfanilamide and N-( 1 -naphthylethylenediamine) in acid solution to produce a colored product with a molar absorptivity of 4.5 X ItHM" 1 cm- 1 at 540 nm. The colored solution is pumped into a 4.5-meter-long, coiled Teflon tube whose fluorocarbon wall has a refractive index of 1.29. The aqueous solution inside the tube has a refractive index near 1.33. The colored solution is pumped through the coiled tube. An optical fiber delivers white light into one end of the tube, and an optical fiber at the other end leads to a polychromator and detector. 

Acid-Base. The pH of natural waters is determined primarily by the carbonate equilibria. However, organisms may produce amounts of organic matter or ammonia sufficient to influence the pH and buffer capacity of the waters. It would be of interest to determine titration curves of high organic, high color, low alkalinity waters leached from some marshes. It is possible that these waters contain sufficient amounts of organic acids to be significant. 

Shapiro, J. 1966. The relation of humic color to iron in natural waters. Verhandlungen Internationale Vereinigung fiir Theoretische und Angewandte Limnologie 16 477—484. 

According to their acidity, humic substances are hydrophobic and are split into two groups humic and fulvic acids. Humic acids are stable molecules originating from the ageing of organic matter. They are responsible for water coloration and represent 40-60% of natural organic matter in rivers and lakes. Fulvic acids are smaller than the humic acids and are generally less aromatic than humic acids extracted from the same pool of DOM. 

Zanardi-Lamardo, E., Clark, C.D., and Zika, R.G., Frit inlet/frit outlet flow field-flow fractionation Methodology for colored dissolved organic material in natural waters, Anal. Chim. Acta, 443, 171, 2001. 

Ohver B. G., Thurman E. M., and Malcolm R. L. (1983) The contribution of humic substances to the acidity of colored natural waters. Geochim. Cosmochim. Acta 47, 2031-2035. 

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