Flow injection analysis of nanomolar silicate using long pathlength absorbance spectroscopy

Area of Science:

• Analytical Chemistry
• Environmental Science
• Materials Science

Background:

• Accurate determination of low-concentration silicate is crucial for marine geochemistry and semiconductor manufacturing.
• Existing methods for nanomolar silicate detection often lack the required sensitivity or throughput.

Purpose of the Study:

• To develop and validate a sensitive, high-throughput analytical method for dissolved silicate determination at nanomolar levels.
• To establish a robust protocol suitable for both marine water samples and high-purity water used in the semiconductor industry.

Main Methods:

• Utilized flow injection analysis (FIA) coupled with long pathlength liquid core waveguide (LCW) spectrometry.
• Employed the ammonium molybdate colorimetric method, with reduction to silicomolybdenum blue by ascorbic acid.
• Optimized reagent concentrations, flow rates, and reaction conditions, including phosphate interference mitigation with oxalic acid.

Main Results:

• Achieved detection limits of 7.2 nM for pure water and 9.0 nM for seawater.
• Demonstrated sample throughput of 12 samples/hour at low levels, increasing to 36 samples/hour at micromolar levels.
• The method proved effective for the targeted analytical range of 10 nM to 5 μM, with potential for extension.

Conclusions:

• The developed FIA-LCW system provides a sensitive and efficient method for nanomolar silicate analysis.
• This technique meets the stringent requirements of the semiconductor industry and is suitable for analyzing oligotrophic ocean waters.
• The method offers improved sensitivity, reduced sample consumption, and higher throughput compared to previous LCW-based spectrophotometric approaches.