title: Liquid-waveguide spectrophotometric measurement of low silicate in natural waters.
abstract: This paper describes a robust, sensitive method for measurement of low silicate in natural water. The method is based on the reaction of silicate with ammonium molybdate to form a yellow silicomolybdate complex, which is then reduced to silicomolybdenum blue by ascorbic acid. This method shows no refractive index effect and a small salinity effect that can be corrected for seawater samples. It was found that the use of poly-vinyl alcohol can prevent the precipitation formation in the ammonium molybdate solution and improve the stability of the silicomolybdenum blue complex. The sensitivity of this method is substantially enhanced by using a liquid-waveguide capillary cell. The detection limit is 0.1 microM, and working range is 0.1-10 microM for using 2-m liquid-waveguide capillary cell (LWCC). The method can be used for both freshwater and seawater samples and has been used to study the distribution of silicate in surface seawater of Gulf Stream in Florida straight.
authors: Ocean Chemistry Division, Atlantic Oceanographic & Meteorological Laboratory, National Oceanic & Atmospheric Administration (NOAA), 4301 Rickenbacker Causeway, Miami, FL 33149, USA.
authors: Natchanon
authors: N
authors: Amornthammarong
authors: Jia-Zhong
authors: JZ
authors: Zhang
mesh_terms: D007202:Indicators and Reagents / Q000737:chemistry; D007267:Injections; D008982:Molybdenum / Q000737:chemistry; D011142:Polyvinyl Alcohol / Q000737:chemistry; D015203:Reproducibility of Results; D054712:Salinity; D012623:Seawater / Q000737:chemistry*; D017640:Silicates / Q000032:analysis*; D017655:Silicon Compounds / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods*; D013594:Syringes; D013997:Time Factors
chemical_list: D007202:Indicators and Reagents; D017640:Silicates; D017655:Silicon Compounds; C013250:silicomolybdate; D008982:Molybdenum; D011142:Polyvinyl Alcohol