Programmable Fow Injection. Principle, methodology and application for trace analysis of iron in a sea water matrix

Area of Science:

• Analytical Chemistry
• Environmental Chemistry

Background:

• Traditional Flow Injection (FI) analysis automates assays but suffers from continuous reagent consumption, waste generation, and suboptimal assay step performance due to fixed flow rates.
• Optimizing reagent-based assays requires balancing different time scales for sample/reagent metering, mixing, incubation, and detection, which is challenging with constant flow systems.

Purpose of the Study:

• To introduce and detail Programmable Flow Injection (pFI) as a novel approach for automated reagent-based assay method development.
• To demonstrate the optimization of an iron assay at nanomolar levels using pFI and its application to seawater analysis.

Main Methods:

• Development of pFI in two variants: Stop in Holding Coil (SHC) and Stop in Flow cell (SFC).
• Optimization of an iron assay protocol using pFI, allowing computer-controlled execution of individual assay steps at optimal flow rates.
• Application of the SFC method for determining dissolved iron (II) in spiked seawater samples.

Main Results:

• The SHC method achieved a Limit of Detection (LOD) of 3.1 ppb (55 nM Fe) with 1.9% r.s.d. precision at ~90 nM, and a sampling frequency of 90 samples/h.
• The SFC method demonstrated superior performance with an LOD of 0.57 ppb (10 nM Fe), 0.8% r.s.d. precision at ~90 nM, and a sampling frequency of 40 samples/h.
• The SFC method's sensitivity was independent of matrix salinity, and results showed good agreement with a manual method for dissolved iron determination in seawater.

Conclusions:

• Programmable Flow Injection (pFI) effectively eliminates drawbacks of traditional Flow Injection, enabling computer-controlled optimization of assay protocols.
• The SFC variant of pFI provides a highly sensitive and precise method for nanomolar iron determination in complex matrices like seawater.
• pFI represents a significant advancement in automated analytical chemistry, offering improved efficiency, reduced waste, and enhanced assay performance.