Sodium citrate doped polypyrrole/PS glass capillary tube sensor for ultra-small volume HCl gas detection.

A sodium citrate (SC) doped polypyrrole (PPy)/PS capillary sensor was prepared for ultra-small volume HCl gas detection. A PS film was formed in advance on the inner wall of a silica glass capillary tube, which enabled us to prepare a high-qualified PPy sensitive film inside the tube. The crystallinity, morphology, microstructure and carrier transport properties of the PPy film were characterized by XRD, SEM, FTIR and Hall effect system, respectively. The results indicated that the as-prepared tube sensor sample was able to detect 0.2 mL 30 ppm HCl gas while the plane-shaped PPy/PS sensor failed to probe. The improvement of sensing properties was attributed to the trend of crystallinity, pore (or gap) morphology and the long-narrow gas cell. The tube-like gas cell and the featured PPy/PS film of the tube sample contribute to sensing the small volume of HCl gas, which may be applied in breath analysis for potential nonintrusive disease diagnosis.