Flow injection amperometric sensor for expedient determination of orthophosphate in soil and water

[eng] Flow injection amperometric sensor is herein proposed for reliable and expeditious determination of orthophosphate in terms of phosphorus content (P) in the environmentally relevant samples. The analytical method is performed by injecting the standard/sample solution into a stream of 0.1 mol L-1 potassium chloride and then merged downstream with 0.5% (w/v) molybdate dissolved in 2.5% (v/v) sulfuric acid solution to form the intermediate, which is 12 molybdophosphate complex in a reaction coil. The intermediate was then electrochemically reduced at a glassy carbon electrode (GCE) with the applied potential of 0.20 V vs Ag/AgCl reference electrode. The reduction of intermediate produced electrical current that is directly proportional to concentration of orthophosphate in the injected solution. Linear ranges for determination of orthophosphate are spanned over three ranges from 10-100 µg P L-1, 0.1-1.0 mg P L-1, and 1-10 mg P L-1, with a detection limit (LOD) of 3 µg P L-1. Relative standard deviations for 11 replicate injections of both 0.5 mg P L-1 and 5 mg P L-1 were 0.8%. A sample throughput of 40-60 injections h-1 was achieved. The proposed method was validated by the analysis of certified reference materials (CRMs) of soil and water, and was successfully applied to reallife environmental samples. Amperometric detection is a straightforward alternative to the conventional spectrophotometric one. Besides, this analytical approach does not deteriorate by interferences such as particulates, colored substances, refractive index effect (Schlieren's effect). Especially, it can tolerate concentrations of silicate and chloride as high as 1 g L-1 and 40 g L 1, respectively

A sensor probe for the continuous in situ monitoring of ammonia leakage in secondary refrigerant systems

Ammonia is becoming more widely used in refrigeration systems due to the phasing out of CFCs and HCFCs. However, ammonia is a toxic gas and its leakage from refrigeration systems can lead to human exposure and contamination of refrigerated food stuffs. There is a lack of devices capable of the direct and continuous monitoring of leakage of ammonia into secondary refrigerant systems. Here we demonstrate an ammonia measurement probe for continuous contact monitoring of secondary refrigerants. The probe was based on an ammonia-sensitive film of inkjet printed polyaniline nanoparticles deposited onto an interdigitated electrode array and enclosed behind a polytetrafluoroethylene membrane. When operated impedimetrically, the probe was capable of the detection of ammonia across the industrially relevant range of 0 to 100 ppm from +4 to -15°C in water and brine. Operation of the probe as a simple threshold alarm without the requirement for temperature monitoring or calibration is illustrated. © 2013 The Royal Society of Chemistry