Reflection photometric detection on a paper-backed immobilized reagent surface in a PDMS microfluidic chip flow injection system integrated with gas diffusion separation

Reflection photometric detection on a pH paper micro-patch in a PDMS microfluidic chip was developed. The microfluidic chip integrated flow injection analysis (FIA) and gas diffusion separation system. The whole system fully integrated all analytical functional components including injection, separation and detection. The system was applied to the detection of ammonium ion. A reproducibility of 4.2% RSD (n=9) was achieved for a 20 MM NH4+ standard. The limit of detection for NH4+ was 0.6 mM (3 sigma) at a sample throughput of 22 h(-1) consuming 400 nL sample volume for each determination.