Elucidation of molybdosilicate complexes in the molybdate yellow method by ESI-MS

Area of Science:

• Inorganic Chemistry
• Analytical Chemistry

Background:

• The molybdate yellow method is a common technique for detecting silicates.
• Understanding the formation mechanism of molybdosilicates is crucial for optimizing analytical methods.

Purpose of the Study:

• To elucidate the formation process of molybdosilicate using electrospray ionization mass spectrometry (ESI-MS).
• To clarify the reaction steps and identify key species involved in molybdosilicate formation at the molecular level.

Main Methods:

• Electrospray ionization mass spectrometry (ESI-MS) was employed to analyze reaction mixtures.
• The study investigated the effect of pH on the hydrolysis of polymeric silicic acids and the subsequent formation of molybdosilicates.

Main Results:

• Polymeric silicic acids were hydrolyzed to monomers, which then formed molybdosilicates with a Keggin structure.
• ESI-MS revealed that molybdosilicate formation occurs between pH 1 and 2.
• Below pH 0.5, excess sulfuric acid prevented molybdosilicate formation, while above pH 2, condensation led to α-molybdosilicate.

Conclusions:

• ESI-MS is a powerful tool for understanding molybdosilicate formation at the molecular level.
• The pH of the reaction medium critically influences the hydrolysis, condensation, and final structure of molybdosilicates.
• This research provides detailed insights into the reaction pathway of molybdosilicate formation.