A first-derivative spectrophotometric method utilizing the zero-crossing measurement technique was developed for the simultaneous determination of phosphate and silicate in synthetic detergents and waters. Two procedures, based on the formation of phospho-and silicomolybdenum blue complexes in the presence of metol and ascorbic acid, were adopted to allow the simultaneous determination of both anions. The P concentration ranges and detection limits for the determination of phosphate in the presence of silicate utilizing the metol and ascorbic acid procedures were 0.12-1.7 and 0.07-1.2 mg mL 21 and 0.07 and 0.02 mg mL 21 , respectively. The corresponding Si concentration ranges and detection limits for the determination of silicate in the presence of phosphate were 0.12-1.5 and 0.08-1.3 and mg mL 21 and 0.06 and 0.02 mg mL 21 , respectively. The relative standard deviations (n = 10) were 0.86-2.8% for 0.43 mg mL 21 P and 0.5 mg mL 21 Si. The proposed procedures were evaluated by a statistical analysis of the analytical data.
Phosphate and silicate have been involved in an environmental problem. The problem has serious consequence in view of the widespread utilization of phosphate and silicate in water softening, surfactants and many other applications. Phosphates were introduced into lakes from inadequately treated sewage containing detergents and water from humans and animals. If in excess quantity, they lower the quality of lake water and cause the death of living organisms by stimulating the growth of alga. Silicate serves as a micronutrient for diatomaceous algae. This type of algae converts soluble silicate to solid silicate, and thus increases the insoluble material percentage of water if used finallys for drinking. 1 Numerous studies have been performed to develop the sensitivity 2-5 and selectivity 6-11 of the polyheteromolybdic acid and polyheteromolybdenum blue procedure, which is a wellknown method to determine the silicate and phosphate. However, the selectivity for the determination of phosphate and silicate in the presence of each other was not sufficient for a direct determination of these anions in material samples. Two well-known procedures were utilized for the simultaneous determination of phosphate and silicate. One was based on kinetic differences in the rates of the formation of two molybdoheteropoly acid 12 and molybdoheteropoly blue. 13 The other procedure was based on utilizing segment flow analysis (FIA). 14 However, these procedures require careful control of the experimental conditions. Derivative spectrophotometry has been found to useful for the direct analysis of mixtures. 15,16 The simultaneous determination of phosphate and silicate in material samples by a simple and inexpensive method was difficult, due to mutual interference between two anions. The main purpose of the present work was the simultaneous determination of phosphate and silicate by a simple, sensitive and selective method utilizing a relatively inexpensive and popular apparatus. Experimental MaterialsAll chemicals were of analytical-reagent grade and were stored in polyethylene bottles to prevent silicate leaching. Twice-distilled water was used throughout. A phosphate stock solution (1 mg PO4 3-mL -1 : a 0.3582 g of oven-dried KH2PO4) was dissolved in 250 mL of water. A silicate stock solution (1 mg SiO3 2-mL -1 : a 0.6969 g of Na2SiO3·5H2O) was dissolved in 250 mL of water. A molybdenum(VI) solution (0.02 M: a 6.1790 g of (NH4)6Mo7O24·4H2O) was dissolved in 250 mL of water. An acidic molybdate solution (1.6 × 10 -2 M (≈2%): a 2.0 g of (NH4)6Mo7O24·4H2O) was dissolved in 100 mL of 0.6 M hydrochloric acid. 1-Amino-2-naphthol-4-sulfonic acid reagent (ANSA) (3.0 × 10 -3 M) was prepared as reported elsewhere. 1 Stannous chloride (1.3 × 10 -2 M (0.25%): a 0.625 g of SnCl2) was dissolved in 250 mL of 0.15 M hydrochloric acid. Detergent and wastewater samples were obtained from Lang Silicate, and sulfonation factories for synthetic detergents, Tenth of Ramadan City, Egypt. Tap water was obtained from the municipal water of the cities Cairo a...
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