A pump-less discrete opto-fluidic chemical spectrophotometry system (DOCSS) for online in situ monitoring of dissolved contaminants in aqueous media

This paper presents the fabrication of a discrete chemical analyzer system for online monitoring of dissolved ions in water using UV-VIS absorption spectrophotometry. The device is composed of three main components: fluidic, optical, and control. The test cell was designed to also function as a non-invasive volume sensor, and the volume sensing principle was based on light scattering by entrapped water droplets. This design eliminates the need for expensive high-precision syringe pumps for sample introduction into the test cell. The discrete opto-fluidic chemical spectrophotometry system device can be interrogated remotely over the internet, and the performance was evaluated using the spectrophotometric analysis of chromium (VI) with di-phenylcarbazide as model chemistry. The results showed very good stability in the optical absorbance measurements, a method detection limit of 6.38 ppb, and good precision of 3.04% RSD (relative standard deviation) at 50 ppb chromium (VI). Also a linear calibration range of 25 to 1,250 ppb was obtained, and the response was reversible.