Influence of reaction temperature on the phosphoantimonylmolybdneum blue method for the determination of phosphate in natural waters and implementation of a step-by-step flow analysis
Date Issued
2015
Date
2015
Author(s)
Wang, Tzu-Yuan
Abstract
This study investigates the influence of reaction temperature on the phosphoantimonylmolybdneum blue method for the determination of phosphate in natural waters. Results show that even though heating can effectively increase the reaction rate but it also changes the spectrum of the final blue color. At 880 nm, the change of the molar extinction coefficient is ca. -0.22 % for an increasing of 1 ℃, and it is a reversible process. If the temperature is elevated when the reaction is developing, the color formation curve would go erratic at higher temperatures and the final absorbance does not return to normal value even a later cooling procedure is carried out. Therefore, the traditional way of heating up the sample using a heating bath higher than 35 ℃ is not recommended. Instead, the measurement should be made at a constant temperature (e.g. 30 ℃). The reaction rate can be improved by using a higher concentration of ascorbic acid. The reagent was prepared in the presence of 1% (w/v) sodium sulfite which preserves the ascorbic acid from oxidation. According to the results mentioned above, an automated flow analyzer was developed based on a stepwise manner. The sample flow was mixed with reagents and filled a thermo-controlled flow cuvette then stopped to allow the color reaction to complete. The precision obtained was better than 0.05 % at a 10 μM level. This system suits well the on-board measurement especially when dealing a batch of sample of various temperatures collected from different depths.
Subjects
Phosphate
Phosphoantimonylmolybdneum blue method
Temperature
Ascorbic acid
Stepwise flow analysis
Type
thesis
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