Papers by Author: Mao Hua Wang

Abstract: Magnetic separation is an emerging and promising technology in biological sample preparation. In this paper, a high-intensity and high-gradient magnetic separation system was developed to separate magnetic nanobeads from aqueous solution. This system mainly consisted of a magnetic separator, a micropump and an electronic timer. The magnetic separator was designed by placing two columns of permanent magnets in an aluminum holder. Two magnets in each column were laid out in repelling mode and a hole between the two columns was used to accommodate a 1.5 ml tube. Working with the electronic timer, the micropump was employed to remove waste solution at a certain rate after magnetic nanobeads captured onto the sides of the tube wall. The experiments for separation of magnetic nanobeads with diameters of 150 nm and 50 nm using the developed magnetic separation system were conducted to optimize the key parameters of the system including nanobeads concentration, separation time and flow rate. The separation efficiencies of magnetic nanobeads increased as the nanobeads concentration and the separation time increased, whereas decreased when the flow rate was increased. Experimental results proved that the proposed magnetic separation system was able to separate magnetic nanobeads (diameters of 150 nm and 50 nm) with separation efficiencies of 99% and 90% in 30 min and 150 min respectively.

Abstract: In recent years, the prolific usage of nitrogenous fertilizers in the agricultural area of China has resulted in inefficient nitrogen usage, environmental pollution and the degradation of the soil fertility. As such, a rapid, low-cost and reliable soil detection method is urgently needed. This study reported on the laboratory evaluation of a solid-state ion-selective electrode, based on a nitrate doped polypyrrole polymer (PPy(NO3-)), for the simultaneous detection of soil nitrate-nitrogen. The potentiometric slope of these PPy(NO3-) electrodes for nitrate was found to be -(53.3±0.8) mV/decade over a linear range of three decades of concentration 10-4～10-1mol/L. It was also found that these electrodes had a nitrate detection limit of 5.0 ×10-5 mol/L. Impacts of soil extractant conditions were also tested. The electrodes displayed better performances for nitrate solutions with pH lower than 7.0. The potentiometric responses of electrodes exhibited a negative drift tendency of 0.6 mV/°C, which was probably caused by changes of the polymer morphology and the solution ionic activity. In order to reduce the interferences of coexisting anion, deionized water was chosen as soil extractant. It is shown that a fast determination of soil nitrate levels for site-specific control of fertilizer application could be realized using the PPy(NO3-) electrodes together with an automatic fluidic control system.