Abstract: Ultrasmall volume measurements of oxidizable compounds including potassium ferrocyanide, hydrazine, H2O2, dopamine and acetaminophen were carried out by coupling a capillary flow injection system with amperometric detection (diagram given). The FIA system consisted of a sample and carrier reservoirs, a fused-silica capillary (120 cm x 52 µm i.d.) and a large-volume wall-jet detector. Vitreous carbon or Pt (for H2O2 or hydrazine) 2 mm diameter discs placed at a 1 mm distance from the capillary outlet served as the working electrode. The reference electrode (Ag/AgCl) and the Pt wire auxiliary electrode were inserted through the cell cover. Amperometric measurements were carried out with an EG^ampG PAR Model 264A voltammetric analyzer. Capillary flow injection experiments were performed at room temperature after applying the desired potential and allowing the transient current to decay. Sample introduction was accomplished by switching between the carrier and sample reservoirs under conditions of gravity flow, employing a flow rate of 32 nl/min and a 15 sec sample introduction. Highly linear calibration plots were obtained and detection limits were 540 fg, 0.7, 1.3 and 8 pg for H2O2, hydrazine, catechol and acetaminophen solutions, respectively.

Abstract: The performance of a small volume constant flow gravity device, was tested for use in Flow Injection Analysis (FIA). This feed device, based on the mounting known as a Mariotte Flask, was tested with FIA titrations of high dispersion coefficient (D > 10). Under the experimental conditions used, this FIA procedure can easily be adapted to use in a teaching laboratory coupled to a low-cost LED colorimeter. The generation of gradient concentrations was done using either a mixing chamber (V = 0.73 mL) or glass or polyethylene tubes of variable length and internal diameter. The procedure was tested using a classical FIA assay of acidity in some commercial liquids. The results are compared to those obtained using a peristaltic pump.