Non-linearity with metal-metal indicator complex reactions in flow-injection analysis

Area of Science:

• Analytical Chemistry
• Environmental Science

Background:

• Flow-injection analysis (FIA) is a common technique for chemical analysis.
• Accurate calcium (Ca2+) determination is crucial in various fields, including environmental monitoring and clinical diagnostics.
• The cresolphthalein complexone (CPC) method is widely used for calcium detection but can suffer from non-linear calibration curves.

Purpose of the Study:

• To improve the linearity of the standard calibration curve in a flow-injection system for calcium determination using the cresolphthalein complexone reaction.
• To investigate the effect of buffer systems on the formation of the calcium-cresolphthalein complexone chromophore.
• To optimize the buffer composition for enhanced accuracy in calcium concentration measurements.

Main Methods:

• Theoretical study of the relationship between calcium concentration, pH, and the formation of the Ca2(CPC)2- complex.
• Experimental optimization of buffer systems in a flow-injection analysis setup.
• Replacement of the organic base 2-amino-2-methylpropan-1-ol with a boric acid-borate buffer system.

Main Results:

• A linear calibration curve for calcium was achieved in the range of 150 to 1000 mg l(-1).
• The boric acid-borate buffer system demonstrated superior performance compared to the organic base.
• The optimized buffer solution consisted of 0.05 mol l(-1) boric acid, 0.05 mol l(-1) KCl, and 35 g l(-1) sodium acetate at pH 8.5.

Conclusions:

• The use of a boric acid-borate buffer system significantly enhances the linearity of calibration curves in flow-injection analysis for calcium.
• This optimized method provides a more accurate and reliable approach for quantifying calcium concentrations.
• The findings contribute to improved analytical methodologies in fields requiring precise calcium measurement.