Simultaneous Determination of Phosphate and Silicate by First-Derivative Spectrophotometry

Abstract

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...

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

“…Similarly, El-Shamy and Iskander found that the reduction of 12-MPA continued up to a 5-to 6-fold molar excess of SnCl 2 over 12-MPA [40]. In methods using heating with organic reductants, 10-fold excesses of hydrazine sulfate and 1-amino-2-naphthol-4-sulfonic acid (ANS) have also been reported as sufficient for complete reduction of 12-MPA [65,73], as the reduction inherently becomes much more favourable and rapid at higher temperatures.…”

“…This effect is clearly shown in the spectra recorded by a number of authors [40,65,85]. If an undesirable shoulder is seen at 820 nm, or the absorption peak is unusually broad, the acidity should be decreased to favour the formation of only the Snsubstituted products [40].…”

Recent Developments of Derivative Spectrophotometry and Their Analytical Applications

“…The individual determinations of fluoride 163 and phosphate 164 and simultaneous determinations of phosphate and silicate 23,165 and nitrate and nitrite 166,45 were reported. Third derivative spectra have been used for the determination of fluoride in technical samples of Leuprolide (an anti-cancer drug for prosthetic cancer).…”

“…Recently, a first derivative spectrophotometric method utilizing zero-crossing technique of measurement has been developed for simultaneous determination of phosphate and silicate in synthetic detergents and water. 23,165 The procedures, based on formation of phospho-and silicomolybdenum blue complexes in the presence of reducing agents were adopted to allow simultaneous determination of both anions. A second order derivative spectrophotometry was applied to the simultaneous of nitrate and nitrite ions in bath solutions for alkaline black-oxidation of steel.…”

Indirect determination of dissolved silicate in surface water using energy-dispersive X-ray fluorescence spectrometry

“…There are a number of different methods for determination of silicate, with spectrophotometric methods most widely used, [10][11][12][13][14][15][16] oen in conjunction with ow injection analysis (FIA), [17][18][19][20] stopped ow injection analysis 21 and sequential injection analysis. 22,23 Most of them are indirect and based on the determination of an element or a molecule associated with a stoichiometric ratio with silicon in a readily isolated compound.…”